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General / Warped DSM in coastal strips (Phantom 4 RTK with GCPs)
« on: September 04, 2019, 01:43:55 AM »
I do coastal surveys and would like some advice for how to deal with surveys over long, thin strips near water.
I recently surveyed a coastal area of 6000 x 200 m with 2300 photos using the Phantom 4 RTK, and used 12 ~evenly spread GCPs with a GNSS system.
I compared the resulting DSM to two previous ones collected by more advanced systems, and found that my model has a clear warp of +/- 2 ft with a radial pattern. Without GCPs, the model warped up to 8 ft, so they certainly helped but did not fix the issue. See the attached image.
I performed the same survey style (P4RTK, GCPs, same height and overlap) on another location that was a 2500 x 1500 m area and the DSM matched perfectly with previous models. Even without GCPs the DSM did not have any warp, just needed a vertical shift. Thus, I think the warp I see may be due to processing a thin strip of land (and possibly the water nearby did not help).
I am looking for any insight into why this warp occurs, and suggestions to help process thin strips of land near water. I'm ready to test different solutions and report back. I am thinking that working in chunks may help, but I have not tested this yet.
The processing report is attached. My general workflow was add PPK cameras, Align, add GCPs, gradual selection and optimize cameras, dense cloud, DSM.
I recently surveyed a coastal area of 6000 x 200 m with 2300 photos using the Phantom 4 RTK, and used 12 ~evenly spread GCPs with a GNSS system.
I compared the resulting DSM to two previous ones collected by more advanced systems, and found that my model has a clear warp of +/- 2 ft with a radial pattern. Without GCPs, the model warped up to 8 ft, so they certainly helped but did not fix the issue. See the attached image.
I performed the same survey style (P4RTK, GCPs, same height and overlap) on another location that was a 2500 x 1500 m area and the DSM matched perfectly with previous models. Even without GCPs the DSM did not have any warp, just needed a vertical shift. Thus, I think the warp I see may be due to processing a thin strip of land (and possibly the water nearby did not help).
I am looking for any insight into why this warp occurs, and suggestions to help process thin strips of land near water. I'm ready to test different solutions and report back. I am thinking that working in chunks may help, but I have not tested this yet.
The processing report is attached. My general workflow was add PPK cameras, Align, add GCPs, gradual selection and optimize cameras, dense cloud, DSM.