The Process and Challenges of Producing High Resolution Orthoimages in the Thousands Using Agisoft Photoscan
Emily Bornestig, University of Northern British Columbia (UNBC)
With a total project area of 4363 km2 (more than 1.5 times the area of all of Luxembourg), producing 2136 orthoimages of the area surrounding BC’s Kootenay Lake (clipped to 1:2500 scale tiles at a 10 cm resolution) presented a host of challenges to be identified and surmounted.
The overall photogrammetric orthomosaic processing in Agisoft Photoscan had to be broken down and handled in smaller portions rather than all at once. Approximately 15,000 air photos were taken at two different altitudes – low for urban areas, and high for wilderness.
I explored different approaches in search of the most efficient workflow while endeavouring to produce the highest quality product, including different ways of portioning up the project area, examining the effectiveness of processing images from one or both altitudes at a time, and how to process as many orthoimages as possible at a given moment.
I addressed several challenges along the way, including difficulty aligning images along the borders of different flight paths, misalignments found during the quality-checking stage, and some inherent weaknesses in the software, such as a ‘swirling’ effect on densely forested areas .