Hi,

An error in GCP elevation is likely to shift your orthoimage. The 28m difference in elevation is the geoid height on this area.

What are the results when you don't use any geoid ?

Regards,

Guillaume

On 10/17/2016 11:15 PM, Félix-Antoine Audet wrote:
I try to refine orthorectification of a World-View 2  image with a set of GCP (17 in total). First i read .geom file in initial image with otbcli_ReadImageInfo and try to refine with otbcli_RefineSensorModel using my GCP. However, resulting orthoimage using refine .geom are more shifted (relative to those GCP) than original images.

Investigating this problem i found that height (z) estimate from otbcli_RefineSensorModel for each GCP are not the same that SRTM data. I use DownloadSRTMTiles application to download srtm data and the geoid link found on the OTB website. Here the result :

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=4222, y=32918, z=215.755, lon=-5.22294, lat=7.16053

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=7818, y=29136, z=215.046, lon=-5.20676, lat=7.17769

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=3015, y=30395, z=224.989, lon=-5.22845, lat=7.17191

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=2146, y=34611, z=227.753, lon=-5.2323, lat=7.15284

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=8825, y=28531, z=207.521, lon=-5.20222, lat=7.18045

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=12964, y=24821, z=252.431, lon=-5.18351, lat=7.19734

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=20593, y=20334, z=263.199, lon=-5.14906, lat=7.2178

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=19766, y=15039, z=259.089, lon=-5.1529, lat=7.24173

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=7572, y=24160, z=221.765, lon=-5.20796, lat=7.20017

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=14997, y=19624, z=238.779, lon=-5.17444, lat=7.22084

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=19236, y=23380, z=237.795, lon=-5.15517, lat=7.20398

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=20686, y=7548, z=259.145, lon=-5.1489, lat=7.27559

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=16714, y=15626, z=244.571, lon=-5.16673, lat=7.23899

2016 Oct 17 16:29:25 : Application.logger (INFO) Adding tie point x=16824, y=22630, z=253.821, lon=-5.16608, lat=7.20731


However, comparing my GCP with the SRTM data at the same location give me those results.

otb elevation estimate coord_z from SRTM
215.755027023967 188
215.045595474306 187
224.989075573357 195
227.752914068815 199
207.520907906166 178
252.431061319575 224
263.198903942292 234
259.089167755502 231
221.765367774753 193
238.779180367023 211
237.794649632177 209
259.145216934172 231
244.570667331594 216
253.821387341010 225

I noticed that their is a relative common 28 m offset between those 2 elevation

Unfortunately, it seems that OTB cannot support GCP Z coordinate as has been reported in https://groups.google.com/forum/#!searchin/otb-users/gcp$20to$20sensor%7Csort:relevance/otb-users/1Qd1mwk9m7g/QHHO-jUCFAAJ

My question remains to know if difference between elevation from my GCP and those estimate by OTB are the source of the shift of the orthorectification.

Thanks,¸

Félix
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