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Compressed Geospatial Image Asset Handling with Express Server By Glen Thompson, Don Johnson, and Jeffrey M. Young

echnological advancements Introduction in geospatial imagery col- In recent years, the volume and variety of geospatial imagery has skyrocketed. Not only has lection in recent years have T the resolution of satellite imagery increased, but so has the complexity. It is now common for resulted in the increasing avail- new satellites to capture multispectral imagery with dozens of bands. Moreover, these im- ability of greater quantities of provements have been matched by the rise of microsatellites and unmanned aerial vehicles, higher quality imagery. This both of which promiseDelivered cheaper by Ingenta and more frequent image collection. availability has been matched IP: 192.168.39.210 On: Sat, 25 Sep 2021 23:23:53 by increasing demand asCopyright: busi- AmericanIn addition Society to traditional for Photogrammetry camera-based and imaging, Remote the Sensing integration of inexpensive laser ness and nonbusiness users have rangefinders, GPS and IMU units has enabled rapid growth of lidar scanning options. grown to expect high-quality Improvements in the sensors themselves have vastly increased the point cloud geospatial imagery in more ap- density and volume of data that can be collected in a short amount of time. plications on more devices. How- Emerging technologies like full waveform, single photon, and Geiger ever, what has not changed is mode will make future point cloud collections even larger and more that the bandwidth available for dense. Moreover, lidar use is expanding from topographic transferring this imagery is lim- mapping into the areas of indoor mapping, oceanographic ited, which means that, in gen- seabed and coastal mapping, facility management, eral, delivery is the bottleneck and emergency response, to name a few. in any workflow involving image These innovations come at the repositories and end users. This expense of vastly increased image file article describes a sophisticat- sizes and numbers, which for modern ed software solution that takes organizations presents new problems in the advantage of the architecture of form of rapidly rising file storage costs and the wavelet-based MrSID and increased complexity when hosting and JPEG 2000 image formats to de- distributing imagery. The need for liver high resolution imagery to reliable and storage-efficient more users, faster, over any con- image delivery has never nection. been more pressing.

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November 2016 Layout.indd 827 10/19/2016 1:36:04 PM tions without duplicating image data. The MrSID Gen- eration 4 format has the additional advantage of being able to store either raster or lidar point cloud data.

With MrSID and JPEG 2000 encoding, images are compressed such that multiple resolution levels of an image, from an overview all the way up to the full reso- lution, are the natural result of this compression. Addi- tionally, because of the way the actual bits representing the image are stored, any portion of an image can be decompressed at any resolution level without the ne- cessity of decoding the entire image. Express Server is built specifically to take advantage of this selective de- compression feature of MrSID and JPEG 2000, extract- In this article, LizardTech presents one solution to this ing the requested scene quickly and converting it to an problem using LizardTech’s Express Server software, image scene in one of several output formats. which utilizes compressed MrSID and JPEG 2000 im- agery to reduce storage costs and decrease image load- ing times. Express Server Architecture Express Server runs on top of an existing web server and provides access to compressed imagery stored on Express Server Overview the server’s file system or on the network. Clients can LizardTech Express Server is an application for rapidly then connect to the web server using multiple protocols, distributing high-resolution satellite imagery, aerial pho- including the OGC (WMS) standard, tographs, and other large raster datasets. Imagery host- the streaming JPEG 2000 Interactive Protocol (JPIP), ed on Express Server is stored in the MrSID, JPEG 2000, and an Express Server-specific web API. Delivered by Ingenta and other compressed image IP:formats 192.168.39.210 that reduce storage On: Sat, 25 Sep 2021 23:23:53 costs and minimizeCopyright: required networkAmerican bandwidth. Society for PhotogrammetryClients and Remote Sensing Express Server imagery can be accessed from any WMS MrSID is a patented compression technology perfected client. WMS is a widely-supported standard that users by LizardTech over twenty years, and JPEG 2000 is an can access to view imagery from web browsers, from ISO-standard (though it was not created spe- desktop GIS applications, from the ExpressZip web ap- cifically for geospatial applications). Both file formats plication included with Express Server, and more. If the rely on similar advanced compression technologies, in- optional Express Server JPIP component is installed, cluding the and arithmetic encoding. then users can also access imagery from JPIP clients. Express Server reads and serves imagery directly from compressed source files to reduce storage costs. This is in Web Server contrast to traditional image servers, also called tile serv- Express Server works in conjunction with an existing ers, which generate and cache tiled images from source web server installation to distribute imagery. Express images hosted on the server. By creating and storing Server is compatible with both the Microsoft IIS web these tiled images, the tile server avoids reading the en- server on Windows and the Apache web server on Linux. tire source image every time that a small portion of the image is requested. Although this increases the efficiency LizardTech Services of the server, it requires duplicating the source image data LizardTech services provide an interface between the at multiple resolutions, such that the cached tiles often web server and the image server. The following list de- occupy several times the disk space of the source image. scribes the LizardTech services created during the in- stallation of Express Server: The exceptional characteristic of Express Server is that it can read directly from compressed images without • Express Server Admin Backend Service. The sacrificing responsiveness and efficiency. This special Admin Backend service or the Express Server quality is due to the wavelet-based nature of the MrSID Agent, processes requests from the Express Server and JPEG 2000 formats, which can be decompressed Manager to start or stop the web server and per- selectively and can incorporate multiple image resolu- form licensing tasks.

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November 2016 Layout.indd 828 10/19/2016 1:19:12 PM • Express Server Tomcat Service. The Tomcat service runs the Express Serv- er web applications, including Express Server Manager for managing Express Server and ExpressZip for image export. • JPIP Service. The JPIP service is an optional service that you can add during the Express Server installation. The JPIP service processes requests from JPIP clients.

Image Server The image server is the core of the Express Server installation and processes all image requests. When users connect to Express Server, the image server receives the image request and renders the image.

By default, Express Server delivers extract- ed scenes as JPEG images. Other options for final delivery format are PNG (.png), GIF Figure 1: Express Server Architecture. (.gif), TIFF (.tif, .tiff), (.bmp), and MrSID Generation 2, 3, or 4 (.sid). MG4 is the most recent evolution of the MrSID format. Express Server can deliver lidar point clouds in In addition to mosaicking datasets together, color bal- MrSID, LAS, or LAZ format. MrSID and LAZ files offer ancing raster imagery, and manipulating data in oth- Delivered by Ingenta compression; LAS is the uncompressedIP: equivalent 192.168.39.210 of LAZ. On:er Sat, ways 25 asSep do 2021MG2 23:23:53and MG3, MG4 enables geospatial Copyright: American Society for Photogrammetryprofessionals to losslessly and Remote compress Sensing 3-banded and mul- Image Data tispectral (including hyperspectral) geospatial data so The source image data distributed by Express Server is that they can make full use of the most up-to-date im- stored on a local or network file system. Express Server agery. MG4 also introduced support for alpha bands, supports MrSID, JPEG 2000, and NITF raster imagery, which remove the problem of speckling in the transpar- along with MrSID, LAS, and LAZ lidar point clouds. ency areas of mosaics.

Supported Image Formats Table 1 illustrates the differences between versions of MrSID and JPEG 2000 are both wavelet-based formats the MrSID format and JPEG 2000. that facilitate the efficiencies of raster data storage and distribution. Because their wavelet-based algorithms Visualizing Image Requests naturally and automatically result in multiple resolu- The diagram below illustrates the round trip of an im- tions of an image within the compressed image file it- age request to Express Server and return of the image self—from the full resolution image down to a low-reso- to the client. Once a client image request is received lution thumbnail—both formats provide the high image by the web server, the request is recognized as belong- quality required by geospatial professionals yet obviate ing to one of the protocols supported by Express Server. costly and time-consuming image pyramiding. The Express Server engine then: • determines what reader to use MrSID images are identified by generation and may • locates and opens the image after consulting the be MrSID Generation 2 (MG2), MrSID Generation 3 various caches (MG3™) or MrSID Generation 4 (MG4™). There are • extracts the requested scene based on requested important differences among them. MG2, the oldest ver- parameters such as level (resolution), width and sion, has a 2GB file size limit and does not support loss- height, and geospatial coordinates less compression. MG3 introduced support for lossless • engages an image writer based on the specified out- compression and a number of other features including put format reprojection, color balancing, despeckling and encoding • delivers the image areas of interest, and removed the 2GB size limit.

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November 2016 Layout.indd 829 10/19/2016 1:19:12 PM Table 1: Support for Common Requirements in LizardTech File Formats.

Output File Format Output Requirement MG2 MG3 MG4 JPEG 2000 Lossy output, maximum 3 bands, cropping allowed, no ad- ü ü ü ü vanced encoding, output file smaller than 2GB Advanced encoding (reprojection, color balancing, despeck- ü ü ü ling, area of interest encoding, etc.) Output file size greater than 2GB ü ü ü Lossless output ü ü ü Mosaic that has MrSID tiles as input ü ü Multispectral input ü ü Optimization ü ü Alpha band ü ü Signed datatypes (e.g. s8, s16) ü ü Arbitrary band mapping ü Per-band compression ü

Hosting Imagery and instructions about how to treat them. For the pur- poses of WMS, a catalog is the same thing as a layer. Express Server hosts imagery directly from a local or net- Catalogs include several configuration options which work file system. This file system-based approach simpli- change how the image appears to users. Additionally, fies image management and requires minimal server ad- catalogs can be organized into catalog groups so that ministration. Administrators can use a simple web-based users can view multiple related image catalogs through administration tool called the Express Server Manager to a single virtual catalog. point Express Server to the location of imagery on the file system and configure Express Server settings.Delivered by Ingenta IP: 192.168.39.210 On: Sat, 25 Sep 2021 23:23:53 Images on the fileCopyright: system correspond American to Society image catalogsfor Photogrammetry Viewing and IRemotemagery Sensing in Express Server. Catalogs are simply image directo- Express Server’s architecture is standards-based, which ries that administrators make accessible on the server. enables rapid image delivery to virtually any client viewer, regardless of the device or the amount of band- Image Catalogs width required. Express Server responds to a request Express Server treats every image as part of a catalog. formulated according to one of three protocols: WMS, The catalog is the basic edifice used by Express Server JPIP, or the Express Server web API. Each request is to organize images and house information about them in the form of a URL.

Figure 2: Visualizing Image Requests.

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November 2016 Layout.indd 830 10/19/2016 1:19:12 PM Protocols The Web Map Service standard (WMS) provides a simple HTTP interface for requesting georefer- enced map images from one or more distributed geospatial databases. A WMS request defines the geographic layer(s) and area of interest to be processed. The response to the request is one or more georeferenced map images (returned as JPEG, PNG, etc.) that can be displayed in a WMS-enabled GIS application. The WMS proto- col is an Open Geospatial Consortium standard, and is nearly universal among GIS applications and GIS viewers.

The JPIP client/server communication protocol is defined in Part 9 of the JPEG 2000 suite of

standards (ISO/IEC 15444-9). JPIP progressively Figure 3: The ExpressZip viewer uses the Express Server API. streams the wavelet coefficients for a requested part of a picture, which saves bandwidth, com- puter processing on the server, and time. It allows for For more information about Web Map Service (WMS) see: speedy viewing of a large image in low resolution or a • The WMS specification, available for download on higher-resolution part of that same image. Using JPIP, it the Open Geospatial Consortium (OGC) website at is possible to stream large images (even several gigapix- http://www.opengeospatial.org/standards/wms. els in size) to relatively lightweight hardware such as smartphones and tablets. For information about JPIP see the following: • Overview of JPEG 2000 (Part 9, JPIP) at http:// Delivered by Ingenta IP: 192.168.39.210 On: Sat,www..org/jpeg2000/. 25 Sep 2021 23:23:53 Conclusion Copyright: American Society for Photogrammetry• The JPIP specification, and Remote Sensingavailable for download at Express Server is a technologically advanced and efficient the International Telecommunication Union (ITU) method of serving raster imagery and lidar data that have website at http://www.itu.int/rec/T-REC-T.808/en. been compressed to MrSID or other efficient formats. Be- cause it is designed to take advantage of the multireso- lution nature of these formats and their support for se- Authors lective decoding, Express Server delivers imagery faster Glen Thompson, Quality Assurance Manager, than other image servers can, especially as the number of Celartem, dba LizardTech concurrent requests and size of imagery increase. Don Johnson, Technical Writer, Celartem, dba Extensis , Global Business Development, Cel- As geospatial image data increases both in quality and Jeffrey M. Young artem, dba LizardTech in quantity, so does user demand for that imagery, es- pecially now that applications with geospatial compo- For further information on Express Server and other nents are in the hands of millions of everyday mobile LizardTech image asset handling software solutions users. Express Server is one of the fastest and most ef- please contact: ficient methods for ensuring that the imagery will be Jeffrey M. Young there whenever and wherever requested by users. Global Business Development, LizardTech 303-815-2254, [email protected] www.lizardtech.com Further Reading For more information about LizardTech Express Serv- er see the following: • The Express Server product page at https://www. lizardtech.com/express-server/overview

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