I recently completed a mapping project for a gravel pit (Steep Rock Pits and Wash Plant). One of the tasks was to measure the volume of the 1" washed gravel pile, stacked by a conveyor belt. I flew the mission and I noted that the subject stockpile would be in the corner of the map. Remembering that edges of the map can sometimes have less "definition" than those items in the center of the map with greater overlap, I elected to fly a second mission over the corner of the pit where the stockpile is located.
I processed both maps and took volume measurements on both. The first map, where the stockpile was on the corner, measured 2700m3 (rounded number for discussion). Ok...
The second map volume measurement of the same pile (keeping the total area of measurement roughly the same) was 2350m3!! What!!??
I know the overlap on the second map, using the subject stockpile as the reference point, was far better than the first one. But would this account for a 10% difference? That is substantial!! Should these measurements, all things considered, not be closer?
Is this a failure in mission planning? Too high? Too fast? More overlap? Should I fly each subject area twice, with the flight paths being 90º to each other? Than render ALL those images together? Or fly the same mission three times, render three models and compare? Every time? I feel that would erode the advantage of using this software.
I believe there is more I can do for mission planning and strategy to obtain the best possible data before I abandon all hope.