applied sciences Article Technological Development and Application of Photo and Video Theodolites Rinaldo Paar 1,* , Miodrag Roi´c 1 , Ante Marendi´c 1 and Stjepan Mileti´c 2 1 Department of Applied Geodesy, Faculty of Geodesy, University of Zagreb, Kaˇci´ceva26, 10000 Zagreb, Croatia; [email protected] (M.R.); [email protected] (A.M.) 2 Department of Photogrammetry, Plc., Borongajska Cesta 71, 10000 Zagreb, Croatia; [email protected] * Correspondence: [email protected] Abstract: Theodolites are fundamental geodetic measuring instruments for all practical geodetic tasks, as well as for experimental geodetic scientific purposes. Their development has a long history. Photo and video theodolites represent the advanced development of classic theodolites. Development started in 19th century, but only in the last 15 years has commercial application been achieved in the geodetic profession. The latest development, called image-assisted total stations (IATS), is a theodolite which consists of a classic robotic total station (RTS) with integrated image sensors. It was introduced in the early 2000s. With the development of theodolites, their application became much wider; today, they can be used for structural and geo-monitoring, i.e., for the determination of static and dynamic displacements and deformations of civil engineering structures such as bridges, dams, wind turbines, and high buildings, as well as natural structures, such as mountain slopes. They can be implemented in geodetic monitoring systems, which are an integral part of engineering structural diagnosis, and they provide essential information about the current condition of the structure. This paper describes the technological development of photo and video theodolites divided into phases according to the main innovations in their development. The application of modern video theodolites Citation: Paar, R.; Roi´c,M.; (i.e., IATS) is presented through several experimental studies that were performed. The procedure of Marendi´c,A.; Mileti´c,S. conducting measurements with this kind of instrument, as well as the analysis of acquired data and Technological Development and achieved results, is elaborated. Lastly, the authors conclude, according to the achieved results, that Application of Photo and Video IATS can today be used for determination of quasi-static and dynamic displacements with small and Theodolites. Appl. Sci. 2021, 11, 3893. high amplitudes. https://doi.org/10.3390/app11093893 Keywords: photo theodolite; video theodolite; IATS; technological development; displacement and Academic Editor: Karel Pavelka deformation monitoring; structural monitoring; geo-monitoring Received: 26 March 2021 Accepted: 22 April 2021 Published: 25 April 2021 1. Introduction Publisher’s Note: MDPI stays neutral A theodolite is a geodetic instrument for measuring horizontal and vertical directions, with regard to jurisdictional claims in i.e., angles in the horizontal and vertical plane. There are optical and electronic theodo- published maps and institutional affil- lites [1–3]. To determine the point positions in the coordinate system, in addition to angles, iations. we must measure the distance between the instrument and the target. We can measure the distances mechanically (with chains and measuring tapes), optically (with optical distance- meters and interferometers), and electronically (with electro-optical distance-meters and electronic distance-meters (EDMs)). The accuracy of mechanically and optically measured distances is low and not appropriate for terrain characteristic point coordinate calculations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. With time, several technological developments have been incorporated into theodolites; This article is an open access article thus, the accuracy of angle and distance determination has significantly increased. Perhaps distributed under the terms and the biggest development of theodolites was its integration with an electronic distance- conditions of the Creative Commons meter (EDM), which emerged around 1940 and became commercially available in the late Attribution (CC BY) license (https:// 1960s [4]. The type of EDM incorporated into modern total station instruments is commonly creativecommons.org/licenses/by/ of the electro-optical type, using infrared and laser light as a carrier signal [3]. Instruments 4.0/). which can measure angles and distances simultaneously, as well as record the results and, Appl. Sci. 2021, 11, 3893. https://doi.org/10.3390/app11093893 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 29 as a carrier signal [3]. Instruments which can measure angles and distances simultane- ously, as well as record the results and, to a certain extent, process them, are called elec- Appl. Sci. 11 2021,tronic, 3893 tachymeters or total stations (TS) [2]. TS instruments are electronic digital theodo- 2 of 29 lites integrated with EDM instruments and electronic data collectors, which are aimed at replacing manual field data recording; they are capable of providing electronic angle read- ings, as well as distanceto a certain measurements extent, process [3]. them, are called electronic tachymeters or total stations (TS) [2]. TS instruments are electronic digital theodolites integrated with EDM instruments and Today, many different sensors and measurement methods are combined in TS, such electronic data collectors, which are aimed at replacing manual field data recording; they as highly accurateare angle capable reading, of providing electronic electronic distance angle readings,measurements as well (EDM) as distance to reflectors measurements [3]. and to any other surfaceToday, (reflectorless many different EDM), sensors tilt correction and measurement by two-axis methods inclinometers, are combined dif- in TS, such ferent types of motorizationas highly accurate to drive angle both reading, the horizontal electronic distance and the measurements vertical motion (EDM) of the to reflectors instruments, servo,and piezo, to any and other magnetic surface (reflectorlessmotors (robotic EDM), total tilt station—RTS), correction by two-axis image CCD inclinometers, (charge-coupled differentdevice) typesor CMOS of motorization (complemen to drivetary metal–oxide–semiconductor) both the horizontal and the vertical sensors motion of the (CCD or CMOS) instruments,for autofocus, servo, automated piezo, and aimi magneticng (i.e., motors automatic (robotic target total recognition station—RTS), (ATR) image CCD and tracking of signal(charge-coupled points), integration device) or CMOS with global (complementary navigation metal–oxide–semiconductor) satellite system (GNSS) sensors positioning, wireless(CCD communication or CMOS) for autofocus, and operation automated using aiming a controller, (i.e., automatic additional target cameras recognition (ATR) and tracking of signal points), integration with global navigation satellite system (GNSS) for documentation (image-assisted total station—IATS), and IATS with a scanning func- positioning, wireless communication and operation using a controller, additional cameras tion (image-assistedfor documentation scanning total (image-assisted station—IASTS). total station—IATS),Due to the rapid and hardware IATS with adevelop- scanning function ment, as can be (image-assistedseen in Figure scanning 1, these totaldiffer station—IASTS).ent sensor classes, Due toeach the rapidwith hardwaretheir specific development, advantages, can asbe canunified, be seen utilized, in Figure and1, these are differentfused as sensor one single classes, (nearly) each with universal their specific instru- advantages, ment [5]. Moderncan TS be are unified, multi-sensor utilized, systems and are fused which as can one determine single (nearly) the universal three-dimensional instrument [5]. Mod- coordinates of targetern TS points are multi-sensor by combining systems horizontal which can angle, determine vertical the three-dimensional angle, and distance coordinates of measurements [6].target points by combining horizontal angle, vertical angle, and distance measurements [6]. Figure 1 shows theFigure technological1 shows the development technological of development TS over the ofyears, TS over i.e., thefrom years, the mid- i.e., from the mid-20th century until today. The main hardware and software, sensor integration, and 20th century until today. The main hardware and software, sensor integration, and their their impact on instrument performances and operator efficiency for conducting the mea- impact on instrumentsurements performances in the field and are shown.operator It efficiency is evident for that, conducting following thethe integration measure- of EDM ments in the fieldwith are theshown. basic It theodolite is evident in that, the following 1960s upon the discovering integration tachymeters, of EDM with the the dimensions basic theodolite inand the weight 1960s ofupon the instrumentsdiscovering decreased, tachymeters, as well the asdimensions the expert and efficiency weight regarding of the the instruments decreased,measuring techniquesas well as andthe ex timepert for efficiency conducting regarding measurements the measuring in the field. tech- Contrarily, niques and time instrumentfor conducting performance measurements and the possibilitiesin the field. for Contrarily, surveying instrument and monitoring perfor- projects have mance and the possibilitiesrapidly increased. for surveying and monitoring projects have rapidly increased. Figure