Final Report A Comparison of Mobile Scanning to a Total Station ...

Iowa DOT SPR RB22-011 Aug 2012ResultsThe following is a summary of topics discussed at the completion of the project.Data Storage and Computer IssuesComputing and storage requirements need to be separated into two distinct categories;Data processing and extraction, versus end-user usage, and tend to be software dependent.Delivered LAS and image files for this project totaled almost 31GB.Data ProcessingAcceptable performance can be achieved with modest hardware such as a dual-coreprocessor (hyper-threading a plus), 32-bit operating system, 4GB RAM, mid-levelgraphics board, 500GB internal hard drive and the ability to attach external drives viaeSATA or USB 3.0 interfaces when needed. However, higher-end hardware does achievemeasurable performance gains and reduced time expenditure. The size of the project datafiles is subject to many variables such as scan density, vehicle travel speed, etc. The RieglVMX-250 produces approximately 500 to 700MB of raw scan data per mile of scanningwhen set for a scan density of 600,000 points per second and travelling at 40 mph. Theraw scan data is stored in a compacted format. There is nearly a 6-fold increase in the sizeof the scan data after post-processing. Camera data, when enabled, producesapproximately 900MB of imagery data per mile using a 2-camera, 5 megapixel system.Data ExtractionData extraction is performed using the final, adjusted LAS files. The Riegl VMX-250system, configured as described, produces approximately 1.0 to 1.4GB of LAS data permile of scan. Extraction tools are capable of segmenting the LAS data into moremanageable working-file sizes. Experience will determine the maximum manageabledata-set size for a particular hardware platform. Systems are capable of loading one mileof LAS data at a time while maintaining acceptable performance during extraction.Clipping of the LAS data outside of the area of interest allows for longer, wider ormultiple segments to be loaded. The primary limitation in our environment is the fact thatMicroStation, at this time, is still 32-bit platform. Certain Microsoft Windows systemsettings will allow MicroStation to access more than 2GB RAM, but MicroStation’saccess to this additional memory is via way of memory paging. When MicroStation offersa 64-bit platform; manageable data set sizes as well as overall performance shouldincrease.End-User UsageThe typical finished products from a scan mission are the CAD design files and the LASpoint cloud files. The CAD files typically produced are indistinguishable fromconventionally derived products. Hardware platforms currently providing satisfactoryperformance will suffer no adverse impacts from the incorporation of scan-derivedproducts. Several free and commercial utilities are available for the viewing of the LASfiles. One example is the free-ware software viewer Quick Terrain Reader, developed byJohns Hopkins University's Applied Physics Lab. Suitable performance is achieved usingthe lower-end systems described above, although larger models will see substantiallyincreased performance when viewed on higher end, 64-bit platforms with greater than4GB RAM and professional grade graphics boards.Page 14 of 19