Laser Scanning and Data Integration for Three-Dimensional Digital Recording of Complex Historical Structures: the Case of Mevlana Museum

International Journal of Geo-Information

Article Laser Scanning and Data Integration for Three-Dimensional Digital Recording of Complex Historical Structures: The Case of Mevlana Museum

Cihan Altuntas 1,*, Ferruh Yildiz 1 and Marco Scaioni 2

1 Department of Geomatics, Engineering Faculty, Selcuk University, Selcuklu, Konya 42075, Turkey; [email protected] 2 Department of Architecture, Built Environment and Construction Engineering, Politecnico di Milano, Milano 20132, Italy; [email protected] * Correspondence: [email protected]; Tel.: +90-332-223-1894; Fax: +90-332-241-0635

Academic Editor: Wolfgang Kainz Received: 3 November 2015; Accepted: 25 January 2016; Published: 18 February 2016

Abstract: Terrestrial laser scanning method is widely used in three-dimensional (3-D) modeling projects. Nevertheless it usually requires measurement data from other sources for full measurement of the shapes. In this study a 3-D model of the historical Mevlana Museum (Mevlana Mausoleum) in Konya, Turkey was created using state-of-the art measurement techniques. The building was measured by terrestrial laser scanner (TLS). In addition, some shapes of the indoor area were measured by a time-of-ﬂight camera. Thus, a 3-D model of the building was created by combining datasets of all measurements. The point cloud model was created with 2.3 cm and 2.4 cm accuracy for outdoor and indoor measurements, and then it was registered to a georeferenced system. In addition a 3-D virtual model was created by mapping the texture on a mesh derived from the point cloud.

Keywords: terrestrial laser scanner; time-of-flight camera; point cloud; registration; three-dimensional modeling; cultural heritage

1. Introduction Cultural assets are extremely important structures to be transferred to next generations as the common heritage of the humanity [1]. Therefore, their documentation is an important facet of this process. In particular, recording their shape, dimensions, colors, and semantics may allow architects to restore their original forms and rebuild them when they would be destroyed [2]. Any kinds of geometric information about the object (volume, length, location, digital elevation model, cross-sections) can be retrieved from three-dimensional (3-D) digital models [3,4]. 3-D modeling has been practiced for many aims such as virtual reality, heritage building information model (HBIM) applications [5,6], documentation of historical structures, physical replication of artefacts [7], among others. It requires collecting and integrating high-density spatial data from the object surface [8]. In the last decade, with the impressive development of digital photogrammetric techniques, scanning and 3-D imaging sensors, 3-D spatial data of architectural objects can be measured very quickly and precisely. Plenty of literature has been published where different approaches are analyzed and compared [3,9–12]. In reality, in many cases their integration in the optimal solution, being imaging and scanning techniques, are quite complementary [8]. Terrestrial laser scanning should be preferred when the target is a complex structure that is difﬁcult to model by means of geometric primitives [13]. It is also increasingly used for digitization of cultural heritage [10]. Many studies about heritage documentation projects have been made by using laser scanning technique singly, or together with

ISPRS Int. J. Geo-Inf. 2016, 5, 18; doi:10.3390/ijgi5020018 www.mdpi.com/journal/ijgi ISPRS Int. J. Geo-Inf. 2016, 5, 18 2 of 16 image based techniques [3,14,15]. Due to object size, shape, and occlusions, it is usually necessary to use multiple scans from different locations to cover every surface [10]. Multiple scan stations can be integrated in a relatively easy way by means of consolidated registration techniques [16–19]. On the other hand, photogrammetry is more suitable for modeling those surfaces that can be decomposed in regular shapes, even though the development of dense matching techniques [20] gave the opportunity to obtain results comparable to terrestrial laser scanners (TLS) in the reconstruction of free-form objects [21,22]. Photogrammetry also has the advantage of being operated by light sensors that can ISPRS Int. J. Geo-Inf. 2016, 5, 18 2 of 16 be carried onboard unmanned aerial vehicle (UAV) systems [23]; such platforms are useful for data acquisitionof consolidated over roofs registration and other techniques non-accessible [16–19]. On places. the other Very hand, often photogrammetry a camera is is integrated more suitable into a TLS instrumentfor tomodeling allow those the contemporary surfaces that can recordingbe decomposed of 3-Din regular shape shapes, and coloreven though information. the development Theof emerging dense matching technology techniques for [20] 3-D gave measurement the opportunity to is obtain range results imaging comparable [24], whichto terrestrial can laser be operated scanners (TLS) in the reconstruction of free-form objects [21,22]. Photogrammetry also has the by meansadvan of time-of-ﬂighttage of being operated (ToF) by cameras.light sensors Suchthat can sensors be carried can onboard instantly unmanned measure aerial vehicle a set (UAV) of 3-D points (point cloud)systems which [23]; such represents platforms the are geometry useful for data of the acquisition imaged over area. roofs Due and to other the non small-accessible size and places. weight, and the capabilityVery often of directlya camera is recording integrated into 3-D a TLS information, instrument to ToF allow cameras the contemporary have a recording great potential of 3-D shape to devise a wide rangeand of color applications information. in the future. The measurement process is based on recording the response The emerging technology for 3-D measurement is range imaging [24], which can be operated by of a modulated laser light emitted by the sensor itself. [25] and [26] exploited a ToF camera and means of time-of-flight (ToF) cameras. Such sensors can instantly measure a set of 3-D points (point image-basedcloud) modeling which represents for 3-D the visualizationgeometry of the imaged of cultural area. Due heritage. to the small On thesize and other weight, hand, and inﬂuences the of the measuringcapability direction of directly inclination recording 3- andD information, material ToF types cameras on distance have a great measurement potential to devise accuracy a wide have been investigatedrange by of [application27]. s in the future. The measurement process is based on recording the response of a In thismodulated study, alaser 3-D light digital emitted model by the of sensor Mevlana itself. [25] Museum and [26] (Konya,exploited a Turkey) ToF camera was and created image-based by combining modeling for 3-D visualization of cultural heritage. On the other hand, influences of the measuring TLS anddirection ToF camera inclination data. and The material outside types of on the distance building measurement were solely accuracy measured have been by investigated laser scanner, by while indoor details[27]. were measured by using both techniques. Virtual models and orthophoto images were createdIn for this important study, a 3-D digital details model by texturingof Mevlana Museum image onto(Konya, the Turkey) point was cloud, created after by combining creating a mesh surface. Thus,TLS and the ToF performance camera data. The of outside ToF cameras of the building for cultural were solely heritage measured (CH) by laser documentation scanner, while has been indoor details were measured by using both techniques. Virtual models and orthophoto images were evaluated in terms of possible new applications. In addition, the accuracy of the 3-D point cloud model created for important details by texturing image onto the point cloud, after creating a mesh surface. was analyzed.Thus, the performance of ToF cameras for cultural heritage (CH) documentation has been evaluated in terms of possible new applications. In addition, the accuracy of the 3-D point cloud model was 2. The Caseanalyzed Study:. Mevlana Museum

Mevlana2. The MuseumCase Study: is Mevlana located Museum in the city center of Konya, Turkey (Figure1). The museum was setup around the mausoleum of Mevlana Jalaluddin Rumi, which was built during the Seljuq period Mevlana Museum is located in the city center of Konya, Turkey (Figure 1). The museum was setup (13th century).around the The mausoleum location of of Mevlana “Dervish Jalaluddin Lodge” Rumi, which which is was currently built during used the as Seljuq a museum period (13th used to be a rose gardencentury). of the The Palace location ofof “ theDervish Seljuq. Lodge “Dervish” which is currently Lodge” used was as gifteda museum by used Sultan to be Alaeddina rose garden Keykubat to Sultanul-Ulemaof the Palace Bahaeddinof the Seljuq. “ Veled,Dervish theLodge father” was gifted of Mevlana. by Sultan TheAlaeddin mausoleum Keykubat to where Sultanul the-Ulema Green Dome (Kubbe-iBahaeddin Hadra) isVeled, located the father was of built Mevlana. with The the mausoleum permission where of the the Green son Dome of Mevlana, (Kubbe-i Hadra) Sultan is Veled, by located was built with the permission of the son of Mevlana, Sultan Veled, by architect Tebrizli Bedrettin architectin Tebrizli 1274 after Bedrettin the death of in Mevlana. 1274 after From thethat time, death the of construction Mevlana. activities From continued that time, up to the the constructionend activitiesof continued the 19th century up to [28]. the end of the 19th century [28].

FigureFigure 1. 1.Mevlana Mevlana Museum. Museum. ISPRS Int. J. Geo-Inf. 2016, 5, 18 3 of 16 ISPRS Int. J. Geo-Inf. 2016, 5, 18 3 of 16

The “Mevlevi Dervish Lodge” and the mausoleum began to serve as a museum under the name “Konya“Konya Asar-ıAsar-ı AtikaAtika Museum”Museum” inin 1926.1926. In 19541954 thethe exhibitionexhibition and arrangement of the museum was revised and the name of thethe museummuseum waswas changedchanged toto thethe MevlanaMevlana Museum [[28].28]. The section where the mausoleum isis locatedlocated isis 30.530.5 mm ˆ× 30.530.5 m m in in size size and and the the courtyard courtyard is is 68 68 m ×ˆ 8484 m m in in size. size. The courtyard of the museum is entered from Dervisan Gate. There are “Dervish“Dervish Rooms”Rooms” along the north and west sides of the courtyard. The south side next to the Matbah and the Hurrem Pasha Mausoleum ends with the Hamusan Gate opened to the Ucler Cemetery. In the east of the courtyard there is is the the main main building building where where Semahane, Semahane, Masjid, Masjid and, theand graves the graves of Mevlana of Mevlana and his family and his members family aremembers located. are The located covered. The fountain covered andfountain “Seb-i and Arus” “Seb pool-i Arus give” pool a novel give touch a novel to thetouch courtyard to the courtyard [28]. [28]. The entrance to the mausoleum of Hazreti Mevlana is from the Chant Room (Figure2). The Chant RoomThe is aentrance dome-covered to the mausoleum square place. of Hazreti Next to Mevlana it, beyond is from the silver the Chant gate thereRoom is (Figure the mausoleum 2). The Chant hall (Huzur-ıRoom is a Pir) dome to- enter,covered which square is roofedplace. Next by three to it, small beyond domes. the silver The thirdgate there dome is isthe called mausoleum Post Dome hall and(Huzur it adjoins-ı Pir) to the enter, Green which Dome is roofed in the north.by three The small mausoleum domes. The hall third is surrounded dome is called by aPost high Dome wall inand the it east,adjoins south, the Green and north. Dome The in the graves north. of The Mevlana mausoleum and his hall son, is surrounded Sultan Veled, by area high located wall in under the east, the Greensouth, Domeand north. [28]. The graves of Mevlana and his son, Sultan Veled, are located under the Green Dome [28].

Figure 2. Ground plan of Mevlana Museum.

The Semahane along with Masjid was built by Suleiman the Magnificent Magniﬁcent in XVI century. The naat chair in in Semahane Semahane,, the the Mutrib Mutrib room room where where musicians musicians lived lived,, and and the thegathering gathering places places belonging belonging to men to menand women and women are preserved are preserved in their in original their original state. state. The Masjid is enteredentered from thethe CeragCerag Gate.Gate. Also, there are transitions with a small door from Semahane and and Huzur Huzur-ı-ı Pir Pir secti sectionsons where where there there are are the the graves. graves. In this In this section, section, the theMuezzin Muezzin Mahvil Mahvil and andthe Mesnevihan the Mesnevihan chair chair are kept are keptin their in theiroriginal original form.form.

3. Materials Materials and and Methods Methods Terrestrial laser scanning (TLS) surveying has been used to creating creating 3-D3-D models models of of historical historical buildings. The main steps of the 3 3-D-D modeling process with this technique are point cloud registration, registration, texture mapping, and geo-referencing, which necessitates connection with the other related spatial data. The high-resolution spatial data measured, like the point cloud, depicts the shape of the object. In ISPRS Int. J. Geo-Inf. 2016, 5, 18 4 of 16

ISPRS Int. J. Geo-Inf. 2016, 5, 18 4 of 16 texture mapping, and geo-referencing, which necessitates connection with the other related spatial data. The high-resolution spatial data measured, like the point cloud, depicts the shape of the addition, the texture data should be mapped to the point cloud, after meshing, for the real visualization object. In addition, the texture data should be mapped to the point cloud, after meshing, for the real of the object. Terrestrial laser scanners are used for measurement of the outside and inside details. In visualization of the object. Terrestrial laser scanners are used for measurement of the outside and inside addition, in the indoor area, complex details that cannot be completely measured with TLS were imaged details. In addition, in the indoor area, complex details that cannot be completely measured with TLS by ToF imaging, which is an affordable tool to accomplish this task. The flowchart in Figure 3 shows were imaged by ToF imaging, which is an affordable tool to accomplish this task. The ﬂowchart in the method followed in the measuring and creation of the 3-D model of the museum. Figure3 shows the method followed in the measuring and creation of the 3-D model of the museum.

Figure 3. The ﬂowchart of the surveying and 3-D modeling methodology. Figure 3. The flowchart of the surveying and 3-D modeling methodology.

3.1.3.1. Terrestrial Terrestrial Laser Laser Scanning Scanning InIn this this study, study, laser scanning measurements measurements were were carried carried out out with with Optech Optech ILRIS ILRIS-3D-3D laser laser scanner scanner dedevice.vice. This This device device can canmeasure measure 2500 points 2500 pointsin a second in a using second direct using ToF method. direct ToF The method.range measurement The range accuracymeasurement is 7 mm accuracy at 100 m. is Its 7 mm minimum at 100 sampling m. Its minimum step (point sampling-to-point step spacing) (point-to-point is 0.001146° spacing) (20 μrad). is ˝ ˝ Beam0.001146 divergence(20 µrad). is 0.009740° Beam divergence (170 μrad). is It 0.009740 records color(170 µdatarad). for It the records meas colorured datapoints for on the the measured basis of thepoints integrated on the camera basis of (six the mega integratedpixel). cameraThe maximum (six megapixel). measurement The maximumrange of the measurement instrument is range1300 m. of ˝ ˝ Itthe makes instrument panoramic is 1300 measurement m. It makess at panoramic220° vertical measurements and 360° horizontal at 220 fieldvertical-of-view, and respectively 360 horizontal [29]. field-of-view,The ability respectively to capture cent [29].imeter accuracy data at high resolution and the rapid response capability affordedThe by ability TLS makes to capture it the centimeter ideal tool accuracyfor quantitative data at measurement high resolution of andarchitectural the rapid buildings. response capabilityTLS may useafforded direct byToF, TLS phase makes-shift it, and the triangulation ideal tool for methods quantitative to measure measurement the distance of architecturalfrom the instrument buildings. to theTLS object may points use direct [30]. The ToF, maximum phase-shift, measurement and triangulation range ofmethods phase-shift to and measure time-of the-flight distance laser scanners from the caninstrument reach, approximately, to the object points five hundred [30]. The maximumto a few thousand measurement meters range away of, respectiv phase-shiftely. and They time-of-flight have been usedlaser for scanners modeling can of reach, building approximately,s and outdoor five objects hundred [31– to33 a]. fewThe thousandmaximum meters range of away, the instruments respectively. basedThey haveon the been triangulation used for method modeling is about of buildings eight meters and outdoor away. Thus objects, it has [31 been–33]. generally The maximum used for range 3-D modelingof the instruments of small objects. based on the triangulation method is about eight meters away. Thus, it has been generallyLaser usedscanning for 3-D data modeling are a benefit of small to creating objects. 3D drawing, virtual models, and orthophoto images of architecturalLaser scanning structures. data are One a benefit of the tolimitations creating 3D of drawing,laser scanning virtual is models, the measurement and orthophoto from imagesground of- basedarchitectural static instrument structures. stations. One of the Thus, limitations multiple of scans laser scanningare frequentl is they required measurement in order from to ground-based model large objects. In this regards, all of the point clouds should be registered into a common reference system. Another limitation of the laser scanning is the equipment cost, which may reach several tens of thousands of U.S. dollars. ISPRS Int. J. Geo-Inf. 2016, 5, 18 5 of 16 static instrument stations. Thus, multiple scans are frequently required in order to model large objects. In this regards, all of the point clouds should be registered into a common reference system. Another limitation of the laser scanning is the equipment cost, which may reach several tens of ISPRSthousands Int. J. Geo of-Inf. U.S. 201 dollars.6, 5, 18 5 of 16

3.3.2.2. Time Time-of-Flight-of-Flight (ToF) ImagingImaging

A SwissRanger®® SR4000SR4000 camera camera was was used used in in this this study study [34 ,[34,35].35]. It has It has size size 65 mm 65 mmˆ 65 × mm 65 mmˆ 68 × mm 68 mmand and weight weight of 470 of 470 g.The g. The imaging imaging sensor sensor has has size size 144 144ˆ ×176 176 pixels pixels and and thethe measurementmeasurement error is 1 cm on its maximummaximum measurement range of 5 mm [[36].36]. The SR4000 camera records 50 frames per second (fps). The The coordinates coordinates (xyz), (xyz), the the amplitude amplitude,, and and confidence confidence values values are are recorded into the measurement files. files. The The origin origin of of the the coordinates coordinates is the is the optical optical axis axis and andoverlap overlapss the camera the camera frontal frontal plane plane(Figure (Figure 4). All4 frames). All frames acquired acquired sequentially sequentially are recorded are recorded in separate in separate measurement measurement files. In files. the case In the of thecase ToF of thecamera ToF is camera kept inis the kept stationary in the stationaryposition during position data during acquisition, data some acquisition, differences some usually differences occur betweenusually occur the measurements between the measurements (frames) recorded (frames) from recordedthe same fromscene. the Such same departures scene. Such are departuresdue to various are systematicdue to various errors systematic that need to errors be modeled that need, and to to berandom modeled, noise. and Therefore, to random if more noise. than Therefore, one measurement if more ofthan the one same measurement image area is of recorded, the same an image average area image is recorded, file can an be average generated image in order file can to minimize be generated noise. in Accordingorder to minimize to the results noise. obtained According by toother the researchers, results obtained a number by other between researchers, 10 and 30 a number frames is between generally 10 adequateand 30 frames to create is generally 3-D models adequate [37]. Theto create self-calibration 3-D models of [ 37 ToF]. The cameras self-calibration has been performed of ToF cameras with varioushas been techniques performed [38]. with The various effect techniquesof distortion [ 38error]. The in the effect coordinate of distortion measurement error in theof the coordinate SR4000 camerameasurement was corrected of the SR4000 by using camera the factory was corrected settings. by The using output the of factory the ToF settings. camera The is a output point ofcloud. the ToFOn thecamera other is hand, a point the cloud. measureme On thent other can also hand, be themade measurement in motion by can handling also be the made ToF in camera motion by by register handlinging differentthe ToF camera 3-D scenes by registering into a single different coordinate 3-D system scenes into[39].a single coordinate system [39].

Figure 4. Coordinate axis of the SwissRanger SR4000 camera.

ToF imaging techniques can be used in several domains. Driver assistance, interactive screen, and ToF imaging techniques can be used in several domains. Driver assistance, interactive screen, biomedical applications are reported in [40]. Even though these processes can be carried out by using laser and biomedical applications are reported in [40]. Even though these processes can be carried out by scanning or photogrammetry, the use of a ToF camera makes data acquisition faster and economically using laser scanning or photogrammetry, the use of a ToF camera makes data acquisition faster and sustainable. Hussmann et al. [34] compared photogrammetry and a ToF camera, in terms of field of economically sustainable. Hussmann et al. [34] compared photogrammetry and a ToF camera, in terms view, conjugate point detection, and measurement. These two methods were examined in the of ﬁeld of view, conjugate point detection, and measurement. These two methods were examined in the automotive industry for driver assistance, accident prevention, automatic brakes, and for determining automotive industry for driver assistance, accident prevention, automatic brakes, and for determining the movements on the road. The ToF camera was found superior to the photogrammetric method. the movements on the road. The ToF camera was found superior to the photogrammetric method. Boehm and Pattinson [41] investigated the exterior orientation of ToF point clouds in relation to a given Boehm and Pattinson [41] investigated the exterior orientation of ToF point clouds in relation to a given reference TLS point cloud. In addition, ToF imaging has been used for object modeling [37,42,43], reference TLS point cloud. In addition, ToF imaging has been used for object modeling [37,42,43], structural deflection measurement [44,45], and human motion detection [46]. Moreover, mobile structural deﬂection measurement [44,45], and human motion detection [46]. Moreover, mobile measurement was carried out by ToF imaging for detecting the route of moving robots [39] or mapping measurement was carried out by ToF imaging for detecting the route of moving robots [39] or mapping indoor environment [47]. indoor environment [47].

ISPRS Int. J. Geo-Inf. 2016, 5, 18 6 of 16

ISPRS Int. J. Geo-Inf. 2016, 5, 18 6 of 16 4. Data Acquisition Process

4.1. Measurement4. Data Acquisition of the Outs Processide Surfaces

4.1.The Measurement outside surfaces of the Outside of the Surfacesmuseum were measured by using a Optech ILRIS-3D terrestrial laser scanner (seeThe outsidesubsect surfacesion 3.1). of The the selected museum spatial were measured sampling by resolution using a Optech was ILRIS-3D about 1.5 terrestrial cm on the laser object walls,scanner ceilings (see, and Subsection floors. 3.1).The Thedoors selected, due spatialto fine samplingdetails and resolution embellishments was about, 1.5were cm measured on the object with a samplingwalls, spatial ceilings, resolution and ﬂoors. of The 1 cm doors, and 3 due mm, to ﬁnerespectively. details and The embellishments, sampling resolution were measured on the roof with (outer surface)a sampling was 3 cm. spatial Each resolution scan was of overlapped 1 cm and 3 mm, with respectively. others for at The least sampling 30% to resolution help co-registration. on the roof The laser(outer scanning surface) measurements was 3 cm. Each of scanthe outside was overlapped surfaces with of the others museum for at least were 30% carried to help out co-registration. from a distance of approxThe laserimately scanning 25 m. measurements The roof was ofmeasured the outside from surfaces the minarets of the museumof Selimiye were Mosque carried located out from near a the museum,distance and of the approximately measuring 25 distance m. The roofwas was approx measuredimately from 60 them. minaretsThe sections of Selimiye of the Mosqueroof that located cannot be measurednear the from museum, there were and the measured measuring by distanceclimbing was onto approximately the roof. A total 60 m. number The sections of 110 oflaser the scanning roof that cannot be measured from there were measured by climbing onto the roof. A total number of stations were set up for measuring the outside surfaces of the museum (Figure 5). Totally, 2,980,000 110 laser scanning stations were set up for measuring the outside surfaces of the museum (Figure5). laser points were recorded. Totally, 2,980,000 laser points were recorded.

FigureFigure 5. The 5. The outside outside of ofthe the museum museum was was measured measured byby laser laser scanner scanner from from 110 1 stations.10 stations. Some Some details details were scanned many times with overlapped measurements. The color legend on the right shows the were scanned many times with overlapped measurements. The color legend on the right shows the repeated measurements (for example, red areas were measured10 times). repeated measurements (for example, red areas were measured10 times). 4.2. Measurement of the Indoor Environment 4.2. Measurement of the Indoor Environment The indoor areas of the museum were measured by TLS with a spatial sampling resolution of 1The cm. Theindoor same areas instrument of the Optechmuseum ILRIS-3D were wasmeasured applied by here. TLS Details with were a spatial measured sampling with a samplingresolution of 1 cm.resolution The same of instrument 3 mm. The indoorOptech environment ILRIS-3D was was applied recorded here. from Details 72 stations were and measured 5,835,000 with points a weresampling resolutionmeasured. of 3 Asmm. the The administration indoor environment of the museum was didrecorded not allow from scanning 72 stations of the and place 5,835,000 where the points tomb were measured.of Mevlana As the is located, administration the measurement of the museum of the ceiling did not of this allow section scanning could notof the be carriedplace where out. With the thetomb of Mevlanaexception is located, of this area,the measurement a SR4000 ToF cameraof the wasceiling used of to this record section any smallcould details not be inside carried the out. museum. With the exceptionThe light of this weight area and, a SR4000 the chance ToF to camera handle thewas ToF used camera to record helped any the small acquisition details of in detailsside the located museum. The inlight positions weight difﬁcult and the to chance cover with to handle TLS. Some the ToF details camera in Huzur-ı helped Pir the and acquisition Masjid were of measureddetails located by in the SR4000 camera from different stations in order to overlap. The point cloud registration and the positions difficult to cover with TLS. Some details in Huzur-ı Pir and Masjid were measured by the integration of TLS and ToF data are illustrated in Section5. SR4000 camera from different stations in order to overlap. The point cloud registration and the integration4.3. Image of AcquisitionTLS and ToF data are illustrated in Section 5. Photorealistic texture mapping was needed to create a virtual-reality (VR) model of the 4.3. Image Acquisition museum [48]. Due to the low resolution of imaging sensors embedded in the adopted TLS and ToFPhotorealistic camera, independent texture mapping images were was acquired needed forto create the mere a virtual purpose-reality of photo-texturing. (VR) model of the museum [48]. Due to the low resolution of imaging sensors embedded in the adopted TLS and ToF camera, independent images were acquired for the mere purpose of photo-texturing. A single-lens reflex (SLR) Nikon D80 camera (pixel array 3872 × 2592, pixel size 6.1 µm, focal length 24 mm), which had been calibrated beforehand [49], was used for image acquisition. The details to be textured were photographed from a frontal position, in order to mitigate perspective distortions and ISPRS Int. J. Geo-Inf. 2016, 5, 18 7 of 16

A single-lens reﬂex (SLR) Nikon D80 camera (pixel array 3872 ˆ 2592, pixel size 6.1 µm, focal length 24 mm), which had been calibrated beforehand [49], was used for image acquisition. The details to be textured were photographed from a frontal position, in order to mitigate perspective distortions and irregularity in color and intensity. The brightness of the image depends upon the light source and camera position. Thus, the images should be taken from proper positions [50,51].

5. CreatingISPRS 3D Int.Point J. Geo-Inf. Cloud 2016, 5, 18 Model 7 of 16

ISPRS Int. J. Geo-Inf. 2016, 5, 18 7 of 16 5.1. Registrationirregularity of Laser in color Scanner and intensity. Measurements The brightness of the image depends upon the light source and camerairregularity position. in color Thus and, the intensity. images should The brightness be taken from of th propere image positions depends [50,51]. upon the light source and The registrationcamera position. of Thus the laser, the images scanner should point be taken clouds from and proper the positions creation [50,51]. and editing of the triangulated (mesh) surface5. Creating was 3D undertaken Point Cloud Model with PolyWorks® software [52]. First of all, the measurement files 5. Creating 3D Point Cloud Model recorded from5.1. Registration TLS were of Laser converted Scanner Measurements to the PIF file format with Optech Parser (ver.4.2.7.2) software. The registration of the point clouds was operated in PolyWorks® IMAlign® module with the 5.1. RegistrationThe registration of Laser of theScanner laser Measurements scanner point clouds and the creation and editing of the triangulated Iterative Closest Point (ICP) method (see Pomerleau® et al. [53] for a review). The point cloud featuring (mesh)The surface registration was undertaken of the laser scannerwith PolyWorks point clouds software and the [52]. creation First and of all,editing the measurementof the triangulated files the largestrecorded(mesh) overlap surface from with TLSwas were respectundertaken converted to with other to thePolyWorks PIF scans file ®format was software selectedwith [52]. Optech First as Parser of a all, reference. (ver.4.2.7.2) the measurement Scanssoftware. files that directly ® ® overlappedrecorded thisThe wereregistrafrom TLS registeredtion were of theconverted point toits clouds to coordinatethe PIFwas file operated format system. inwith PolyWorks Optech After Parserthe IMAlign registration(ver.4.2.7.2) module software. with of this the group of scans to theIterative reference,The Closestregistra the Pointtion process of(ICP) the methodpoint continued clouds (see Pomerleau was up operated to include et al. [53]in PolyWorks allfor a remaining review® IMAlign). The scans. point® module cloud featuringwith the the largest overlap with respect to other scans was selected as a reference. Scans that directly In orderIterative to apply Closest ICP, Point initial (ICP) registrationmethod (see Pomerleau parameters et al. [53] were for obtaineda review). The from point the cloud manual featuring measurement overlappedthe largest this overlap were with registered respect to toits othercoordinate scans system. was selected After the as registration a reference. of Scansthis group that of directly scans of at leasttooverlapped three the reference, common this werethe pointsprocess registered continued (from to its natural coordinate up to include details system. all suchremaining After asthecorners, registrationscans. edges, of this group or distinctive of scans details). Then, the fineto theIn registration reference, order to apply the wasprocess ICP, applied initial continued registration with up theto parameters include ICP method. all wereremaining obtained After scans. registeringfrom the manual all measurement scans in this way, the global registrationof at leastIn order three was to common apply accomplished ICP, points initial (from registration to natural minimize detailsparameters thesuchcumulative wereas corners, obtained edge errorsfroms, or thedistinctive originated manual details).measurement from Then, consecutive the fine registration was applied with the ICP method. After registering all scans in this way, the global registrations.of at Inleast the three global common registration, points (from the natural registration details such of as all corners, the scans edges, withor distinctive respect details). to the Then, reference data registrationthe fine registration was accomplished was applied with to minimize the ICP method. the cumulative After registering errors all originated scans in this from way, consecutive the global set were performedregistrations.registration simultaneously. wasIn the accomplished global registration, The to minimize maximum the registration the root cumulative of all mean the scans square errors with originated error respect (RMSE) to fromthe reference ofconsecutive scan data registrations after the globalsetregistrations. were registration performed In the simultaneously.global was registration, 2.5 cm. The Inthe maximumthe registration first ro stage,ot of mean all the TLS square scans point error with clouds (RMSE)respect toof of thescan outdoor reference registrations (Figuredata 6) and indoor (Figureafterset were the7) performedglobal environments registration simultaneously. werewas 2.5 independently Thecm. maximumIn the first ro stage,ot registered. mean TLS square point Then,errorclouds (RMSE) theseof outdoor of were scan (Figure registrations combined 6) and with the indoor (Figure 7) environments were independently registered. Then, these were combined with the georeferencingafter the stage global that registration is illustrated was 2.5 cm. in SectionIn the first6. stage, TLS point clouds of outdoor (Figure 6) and georindooreferencing (Figure stage7) environments that is illustrated were independentlyin Section 6. registered. Then, these were combined with the georeferencing stage that is illustrated in Section 6.

Figure 6. The outside 3-D point cloud model of the Mevlana Museum. The images are from west (left) Figure 6. The outside 3-D point cloud model of the Mevlana Museum. The images are from west (left) andFigure north 6. The (right outside) sides. 3- D point cloud model of the Mevlana Museum. The images are from west (left) and north (right) sides. and north (right) sides.

Figure 7. The inside 3-D point cloud model with color. Figure 7. The inside 3-D point cloud model with color. Figure 7. The inside 3-D point cloud model with color. ISPRS Int. J. Geo-Inf. 2016, 5, 18 8 of 16 ISPRS Int. J. Geo-Inf. 2016, 5, 18 8 of 16 5.2. Registration of ToF Camera Point Clouds

5.2. Registration of ToF Camera Point Clouds 5.2.1. Case 1: Measurement of the Mihrab in Huzur-ı Pir Section 5.2.1.In Huzur Case- 1:ı Pir Measurement section, the of Mihrab the Mihrab next intoHuzur-ı the silver Pir sill Section was measured using a SR4000 ToF camera. Fifty framesIn Huzur-ı were recorded Pir section, from the a Mihrab distance next of to4.5 the m silver at two sill stations. was measured This measurement using a SR4000 distance ToF camera. resulted in a meanFifty framesobject sampling were recorded spatial from resolution a distance of 2.0 of 4.5cm m(angular at two stations.resolution This 0.24 measurement degrees). The distance integration time resultedwas set into a30 mean (unit object is arbitrary) sampling and spatial the resolutionmodulation of frequency 2.0 cm (angular was set resolution to 15 MHz. 0.24 degrees).The average measurementThe integration files time(Figure was 8) set of to the 30 (unitraw isframes arbitrary) from and both the modulationstations were frequency created was using set toMatlab 15 MHz.® code. The average measurement ﬁles (Figure8) of the raw frames from both stations were created using ToF point clouds have more mistaken points, especially close to the edge of the frame. Thus, the parts Matlab® code. ToF point clouds have more mistaken points, especially close to the edge of the frame. that have error-prone points on the edge were removed from the point clouds. Then, the second point Thus, the parts that have error-prone points on the edge were removed from the point clouds. Then, the cloudsecond was registered point cloud to was the registeredcoordinate to system the coordinate of the first system (reference) of the ﬁrst point (reference) cloud with point 1 cloud.9 cm withstandard deviation1.9 cm by standard using ICP. deviation by using ICP.

FigureFigure 8. The 8. The Mihrab Mihrab in inHu Huzur-ızur-ı Pir Pir section section was was measured with with a a SR4000 SR4000 camera camera from from two two stations. stations. IntensityIntensity images images (top (top), and), and point point clouds clouds ( (belowbelow).

5.2.2.5.2.2. Case Case 2: Meas 2: Measurementurement of ofMihrab Mihrab on on the the Masjid Masjid The Mihrab of the Masjid was captured with a SR4000 ToF camera from three different stations. The Mihrab of the Masjid was captured with a SR4000 ToF camera from three different stations. Forty images were recorded from each station (Figure9). The distance between the camera station Forty images were recorded from each station (Figure 9). The distance between the camera station and and the measured Mihrab was approximately 4 m at three points-of-view. The mean object spatial the measuredsampling resolutionMihrab was at thisapprox measurementimately 4 m range at three was point 1.7 cm.s-of The-view. second The and mean the object third pointspatial clouds sampling resolutionwere registered at this measurement using ICP with range 1.6 cmwas and 1.71.7 cm. cm The standard second deviations, and the third respectively, point clouds by assuming were registered the usingﬁrst ICP scan with as 1.6 reference. cm and 1.7 cm standard deviations, respectively, by assuming the first scan as reference. ISPRS Int. J. Geo-Inf. 2016, 5, 18 9 of 16 ISPRS Int. J. Geo-Inf. 2016, 5, 18 9 of 16

Figure 9. 9. TheThe Mihrab Mihrab in Masjid in Masjid was wasmeasured measured from three from stations three sta withtions a SR4000 with camera.a SR4000 The camera. registration The registrationof the measurements of the measurements relation to therelation ﬁrst pointto the cloudfirst point was appliedcloud was by applied ICP. Intensity by ICP. images Intensity (top images), and (combinedtop), and combined point clouds point (below clouds). (below).

5.3. Integration of ToF Camera and TLSTLS Data The gate between the mausoleum and the Semahane was measured with both laser scanning and The gate between the mausoleum and the Semahane was measured with both laser scanning and ToF imaging techniques. Thus, the measurements needed to be integrated. Laser scanning surveying was ToF imaging techniques. techniques. Thus Thus,, the the measurements measurements needed needed to be to beintegrated. integrated. Laser Laser scanning scanning surveying surveying was accomplished with an average spatial resolution of 1.2 cm on the object surface, while ToF imaging accomplishedwas accomplished with with an average an average spatial spatial resolution resolution of 1.2of1.2 cm cm on on the the object object surface, surface, while while ToF ToF imaging provided a spatial resolution of approximately 1 cm. After creating the average image file from multiple provided a a spatial spatial resolution resolution of approx of approximatelyimately 1 cm. 1 After cm. Aftercreating creating the average the average image file image from ﬁlemultiple from frames imaged by the ToF camera, both point clouds were integrated by using ICP (Figure 10). The RMSE framesmultiple imaged frames by imaged the ToF by camera, the ToF both camera, point both clouds point were clouds integrated were integratedby using ICP by (Figure using ICP 10). (FigureThe RMSE 10). of registration resulted in a resolution of 1.9 cm. ofThe registration RMSE of registrationresulted in a resultedresolution in of a resolution1.9 cm. of 1.9 cm.

FigureFigure 10. 10. TheThe point point clouds clouds of of the the ToF ToF camera and TLS were combined with ICP.

6. Geo Georeferencingreferencing and and 3D 3D Model Model Accuracy Accuracy Evaluation Evaluation We grouped togethertogether the finalfinal georeferencing of any point clouds in a common reference frame and the assessment of of 3 3-D-D model accuracy because both were based on the measurement of an independent set of control points (CP). These consisted of thirty-sixthirty-six control pointspoints thatthat couldcould bebe wellwell distinguisheddistinguished in the TLS/ToF point clouds (Figure 11). A local geodetic 3-D network was set up to measure CP coordinates. A Topcon GPT-3007N theodolite was employed for this purpose, which allowed for ISPRS Int. J. Geo-Inf. 2016, 5, 18 10 of 16 in the TLS/ToF point clouds (Figure 11). A local geodetic 3-D network was set up to measure CP ISPRScoordinates. Int. J. Geo-Inf. A Topcon2016, 5, 18 GPT-3007N theodolite was employed for this purpose, which allowed10 of for 16 measuring CP 3-D coordinates thanks to the integrated reflectorless rangefinder. Considering the measuringintrinsic measurement CP 3-D coordinates precision thanks of such to the an integrated instrument, reflectorless the error rangefinder. related to the Considering determination the intrinsic of the measurementnetwork’s stations, precision and of the such use an of instrument, reflectorless the mode, error the related precision to the of determination CPs has been of evaluated the network to be’s stations,better than and˘ the5 mm use inof allreflectorless directions mode, [54]. This the precision precision of is CPs superior has been to the evaluated one of 3Dto be points better from than TLS ± 5 mmand in ToF all imaging. directions [54]. This precision is superior to the one of 3D points from TLS and ToF imaging.

Figure 11. 11. ControlControl points points were were measured measured from from traverse traverse points. points. Georeferencing Georeferencing of the ofinside the andinside outside and outsidepoint cloud point models cloud were model executeds were by groundexecuted control by ground points. The control accuracy points. of the The georeferencing accuracy of was the georeferencingassessed by check was points. assessed by check points.

The indoor and outdoor point clouds were georeferenced and aligned by using 3-D rigid-body The indoor and outdoor point clouds were georeferenced and aligned by using 3-D rigid-body transformations on the basis of CPs, whose coordinates were identified in the 3-D model. After transformations on the basis of CPs, whose coordinates were identiﬁed in the 3-D model. georeferencing, the accuracy assessment was carried out by using a set of check points (ChP) made up After georeferencing, the accuracy assessment was carried out by using a set of check points (ChP) of those CPs that had not been adopted for georeferencing. The metric used for evaluating the accuracy made up of those CPs that had not been adopted for georeferencing. The metric used for evaluating was the RMSE of 3-D residuals on ChPs (Table 1). The average residuals of the ChP coordinates were the accuracy was the RMSE of 3-D residuals on ChPs (Table1). The average residuals of the ChP less than one centimeter and their standard deviations were about 2 cm. These are very good results coordinates were less than one centimeter and their standard deviations were about 2 cm. These are when compared to the average point spacing (ranging between 1 cm and 3 cm) of laser scanning data. very good results when compared to the average point spacing (ranging between 1 cm and 3 cm) On the other hand, a rigorous quality assessment was carried out by the comparison of CPs distances of laser scanning data. On the other hand, a rigorous quality assessment was carried out by the between coordinates in the point cloud to the ones in the geodetic measurements. Globally, two subsets comparison of CPs distances between coordinates in the point cloud to the ones in the geodetic of 16 and 20 CPs were selected for quality assessment of indoor and outdoor point clouds, respectively. measurements. Globally, two subsets of 16 and 20 CPs were selected for quality assessment of indoor The average results showed high accuracy of 3-D modeling (Table 2 and Table 3). According to these and outdoor point clouds, respectively. The average results showed high accuracy of 3-D modeling results, the accuracy of the obtained 3-D point cloud model was positively evaluated. (Tables2 and3). According to these results, the accuracy of the obtained 3-D point cloud model was positively evaluated. Table 1. The georeferencing results of inside and outside point cloud model of the Mevlana Museum.

Point Control Check Average Residuals (m) Std.Dev.of Residuals (m) Cloud Points # Points # dx dy dz σx σy σz Outside 6 10 0.005 −0.002 −0.004 0.022 0.013 0.007 Inside 9 11 0.014 −0.004 0.007 0.020 0.026 0.026

ISPRS Int. J. Geo-Inf. 2016, 5, 18 11 of 16

Table 1. The georeferencing results of inside and outside point cloud model of the Mevlana Museum.

Point Control Check Average Residuals (m) Std.Dev.of Residuals (m) Cloud Points # Points # dx dy dz σx σy σz Outside 6 10 0.005 ´0.002 ´0.004 0.022 0.013 0.007 Inside 9 11 0.014 ´0.004 0.007 0.020 0.026 0.026

Table 2. The quality assessment criteria (df ) for the outside 3-D point cloud model of the Mevlana Museum.

Control/Check ITRF-2005 TLS Distance (m) Discrepancy (m) df (m) Point Line Distance (m) 522–525 13.716 13.705 ´0.011 525–510 3.066 3.052 ´0.014 510–521 8.880 8.902 0.021 521–524 4.207 4.218 0.011 524–523 6.314 6.278 ´0.035 523–520 24.658 24.654 ´0.004 520–519 9.157 9.167 0.010 519–514 38.744 38.714 ´0.030 0.023 514–515 3.566 3.541 ´0.024 515–4519 34.237 34.255 0.018 4519–3512 2.535 2.565 0.030 3512–4514 9.661 9.647 ´0.014 4514–4511 1.611 1.573 ´0.038 4511–4520 8.293 8.332 0.038 4520–4518 1.974 1.965 ´0.008

Table 3. The quality assessment criteria (df ) for the inside 3-D point cloud model of the Mevlana Museum.

Control/Check ITRF-2005 TLS Distance (m) Discrepancy (m) df (m) Point Line Distance (m) 707–708 1.277 1.295 ´0.018 708–722 15.951 15.982 ´0.030 722–723 1.161 1.148 0.013 723–721 3.089 3.054 0.035 721–715 21.408 21.425 ´0.017 715–716 2.440 2.445 ´0.004 716–724 17.087 17.060 0.027 724–725 1.252 1.222 0.030 725–706 18.098 18.106 ´0.008 706–726 13.440 13.411 0.029 0.024 726–727 0.680 0.694 ´0.015 727–710 15.200 15.169 0.031 710–700 25.912 25.912 0.001 700–701 1.296 1.316 ´0.020 701–704 2.328 2.365 ´0.037 704–717 5.136 5.117 0.019 717–719 3.217 3.249 ´0.032 719–712 23.744 23.754 ´0.010 712–714 2.559 2.594 ´0.035

7. Texture Mapping Although the 3-D point cloud model represents the shape of the measured object, it does not have texture data to render a realistic visualization. When the texture data of the object is requested to be ISPRS Int. J. Geo-Inf. 2016, 5, 18 12 of 16 recorded in addition to the geometric data, a photorealistic texture has to be mapped on the point cloud after meshing to obtain a continuous surface connecting discrete points. Thus, both geometry and texture data can be visualized together. In order to map the texture, ﬁrst the triangulated (mesh) model surface has to be derived from the raw point cloud [48]. The triangulated model depicts the model shape with triangles adjacent to each other through the object surface. ISPRSTexturing Int. J. Geo-Inf. images 2016, 5, 1 over8 a mesh requires the knowledge of the camera interior orientation12 andof 16 exterior orientation of any stations [49]. The former can be obtained from the preliminary camera calibration. The The latter latter may may be be computed computed by byfollowing following one oneof the of photogrammetric the photogrammetric procedures procedures for image for imageorientation. orientation. In this In case, this case,the presence the presence of several of several ima images,ges, which which are are not not well well connected connected in in a photogrammetric network, network, led led us us to prefer the space resection resection method for computing computing the exterior exterior orientation in an independentindependent way for for any any camera camera stations. stations. This task, task, theoretically,theoretically, requiredrequired the the computationcomputation of of at at least least three three corresponding corresponding control control points points (CP) (CP) visible visible in both in boththe image the image and the and mesh. the mesh.Alternatively, Alternatively, ground ground control control points points(GCP) (GCP)can be can used. be Due used. to Due some to numerical some numerical problems problems (space (spaceresection resection models models are non are-linear), non-linear), usually usually the computational the computational methods methods requi requirere more more points, points, a fact a that fact thatmay mayalso alsoincrease increase the redundancy the redundancy of the of observations. the observations. The triangulatedtriangulated surface was createdcreated inin PolyWorksPolyWorks®® software. Unlike in many softwaresoftware packagespackages thatthat implement implement the the triangulation triangulation process process is 2.5- isD, 2.5-D, in PolyWorks in PolyWorks® a real 3®-Da data real triangulation 3-D data triangulation can be done. canAfter be creating done. Afterthe mesh creating model, the editing mesh model,was required editing to wasfix some required residual to ﬁx problems. some residual The triangulated problems. Theimage triangulated of the dome image belonging of the to dome Semahane belonging can be to seen Semahane on Figure can 12. be seen on Figure 12.

Figure 12. 12. TheThe point point cloud cloud (top-left (top), -leftsolid), (top solid-right (top), -andright mesh), and (below mesh) visualization (below) visualization of Semahane of’s Semahane’sdome. dome.

PI-3000 software (ver. 3.21) was used to map photo-texture on the triangulated model of the PI-3000 software (ver. 3.21) was used to map photo-texture on the triangulated model of the museum. The triangulated model from PolyWorks was transferred to PI-3000 software using the DXF museum. The triangulated model from PolyWorks was transferred to PI-3000 software using the format. The images captured by the Nikon D80 camera were also imported into the software. The DXF format. The images captured by the Nikon D80 camera were also imported into the software. photographs which will be used for texture mapping were selected interactively. They were registered The photographs which will be used for texture mapping were selected interactively. They were to the object (point cloud) coordinate system with conjugated points chosen from the photograph and registered to the object (point cloud) coordinate system with conjugated points chosen from the the point cloud. Then, 3-D virtual models and orthophoto images [55] were created by mapping photo- photograph and the point cloud. Then, 3-D virtual models and orthophoto images [55] were created textures onto the triangulated model (Figure 13). Similarly, the triangulated and texture-mapped by mapping photo-textures onto the triangulated model (Figure 13). Similarly, the triangulated models of the Mihrabs in Huzur-ı Pir section and the door of the Masjid were created (Figure 14). and texture-mapped models of the Mihrabs in Huzur-ı Pir section and the door of the Masjid were created (Figure 14).

Figure 13. Orthophoto and texture mapped 3-D model of the dome of Semahane. ISPRS Int. J. Geo-Inf. 2016, 5, 18 12 of 16

calibration. The latter may be computed by following one of the photogrammetric procedures for image orientation. In this case, the presence of several images, which are not well connected in a photogrammetric network, led us to prefer the space resection method for computing the exterior orientation in an independent way for any camera stations. This task, theoretically, required the computation of at least three corresponding control points (CP) visible in both the image and the mesh. Alternatively, ground control points (GCP) can be used. Due to some numerical problems (space resection models are non-linear), usually the computational methods require more points, a fact that may also increase the redundancy of the observations. The triangulated surface was created in PolyWorks® software. Unlike in many software packages that implement the triangulation process is 2.5-D, in PolyWorks® a real 3-D data triangulation can be done. After creating the mesh model, editing was required to fix some residual problems. The triangulated image of the dome belonging to Semahane can be seen on Figure 12.

Figure 12. The point cloud (top-left), solid (top-right), and mesh (below) visualization of Semahane’s dome.

PI-3000 software (ver. 3.21) was used to map photo-texture on the triangulated model of the museum. The triangulated model from PolyWorks was transferred to PI-3000 software using the DXF format. The images captured by the Nikon D80 camera were also imported into the software. The photographs which will be used for texture mapping were selected interactively. They were registered to the object (point cloud) coordinate system with conjugated points chosen from the photograph and the point cloud. Then, 3-D virtual models and orthophoto images [55] were created by mapping photo- textures onto the triangulated model (Figure 13). Similarly, the triangulated and texture-mapped ISPRS Int. J. Geo-Inf. 2016, 5, 18 13 of 16 models of the Mihrabs in Huzur-ı Pir section and the door of the Masjid were created (Figure 14).

ISPRS Int. J. Geo-Inf.Figure 2016 ,13. 5, 1 Orthophoto8 and texture mapped 3-D3-D model ofof thethe domedome ofof Semahane.Semahane. 13 of 16

FigureFigure 14. 14. TextureTexture mapped mapped 3 3-D-D models models of of Mihrabs Mihrabs in in Huzur Huzur-ı-ı Pir Pir section section (left (left, middle, middle) and) and the the door door of Masjidof Masjid (right (right). ).

8.8. Conclusions Conclusions InIn this this study, study, a 3-D3-D model of the Mevlana Museum (Konya, Turkey) Turkey) was created using TLS and ToF imaging datasets. While While the the application application of of TLS TLS for for 3 3-D-D modeling of cultural heritage has been largelylargely proved proved to to be be effective effective in in projects projects carried carried out out so so far, far, here here,, the the usability usability of of a a ToF ToF camera in documentationdocumentation studies studies of of historical historical structures structures was was investigated. investigated. The The areas areas that that cannot cannot be be measured with laser scanning were were measured measured by by a a ToF camera and a finalfinal unique point cloud model wwasas generatedgenerated by by merging merging both both datasets. datasets. In In fact, fact, ToF ToF cameras cameras can can be be handled handled with with ease ease due due to to the light weight and and the the capability capability of ofrecording recording images images when when in motion. in motion. However, However, the short the shortmeasurement measurement range ofrange the ToF of the cameras ToF cameras can be canseen be as seena drawback as a drawback of this te ofchnology, this technology, even though even this though limitation this limitation is going tois goingbe overcome to be overcome in future insensors. future In sensors. addition, In addition,since the point since cloud the point of ToF cloud camera of ToF does camera not have does any not color,have anyit is difficult color, it to is difficultselect details. to select These details. deficiencies These limit deficiencies the use of limit a ToF the camera use of ain ToF full camera3-D model in fulling studies.3-D modeling studies. TheThe object object spatial spatial sampling sampling resolution resolution at at the the maximum maximum measurement measurement distance distance from from the the camera camera is approxis approximatelyimately 2 cm. 2 cm. The The point point clouds clouds recorded recorded by by the the ToF ToF cameras cameras can can be be combined combined using using ICP registration.registration. Moreover, Moreover, integration integration of of point point clouds clouds from from t thehe ToF ToF camera and laser scanner can can be be also also accomaccomplishedplished using using ICP. ICP. TheThe t terrestrialerrestrial laser scanning method, which which has has been used for modeling historical structures forfor nearly nearly twenty twenty years, years, has has been been proved proved to to be be an an efficient efficient measurement measurement technique technique in in the the field field of culturalcultural heritage heritage documentation. documentation. The The laser laser scanning scanning of of indoor indoor and and outdoor outdoor surfaces surfaces were were performed performed inin six six days. days. T Thehe measurement measurement of of the the roof roof and and indoor indoor complex complex details details w wasas e especiallyspecially time time consuming. consuming. OnOn the the other other hand hand,, large large scale scale data data is is a aburden burden on on computer computer capacity. capacity. The The computer computer that that was was used used to processto process the thedata data had had an Intel an Intel Core Core i5-2400 i5-2400 CPU CPUprocessor processor and 8 and GB RAM. 8 GB RAM. The process The process required required about five days for completion. At the end of this project, all the details of the Mevlana Museum were measured and the 3-D virtual model was created. The quality assessment showed that the point cloud models were created with high accuracy despite of the large number of measurements and the complex structure of the building. On the other hand, georeferencing of the measurements was made by using adequate numbers of control points with high accuracy. In addition, texture mapping with digital images recorded by an independent SLR camera allowed an increase in the information content of the final 3-D model.

Acknowledgments: This study was funded by The Scientific and Technological Research Council of Turkey (TUBITAK) with project number 112Y025.

Author Contributions: Cihan Altuntas was the primary author of this article. Each of the co-authors Ferruh Yildiz and Marco Scaioni contributed to the article on a roughly equally basis. All authors reviewed the final version of the article.

Conflicts of Interest: The authors declare no conflict of interest. ISPRS Int. J. Geo-Inf. 2016, 5, 18 14 of 16 about ﬁve days for completion. At the end of this project, all the details of the Mevlana Museum were measured and the 3-D virtual model was created. The quality assessment showed that the point cloud models were created with high accuracy despite of the large number of measurements and the complex structure of the building. On the other hand, georeferencing of the measurements was made by using adequate numbers of control points with high accuracy. In addition, texture mapping with digital images recorded by an independent SLR camera allowed an increase in the information content of the ﬁnal 3-D model.

Acknowledgments: This study was funded by The Scientific and Technological Research Council of Turkey (TUBITAK) with project number 112Y025. Author Contributions: Cihan Altuntas was the primary author of this article. Each of the co-authors Ferruh Yildiz and Marco Scaioni contributed to the article on a roughly equally basis. All authors reviewed the final version of the article. Conflicts of Interest: The authors declare no conflict of interest.

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