Coordinate System Problem; Kertau RSO / RSO Malaya (m) (EPSG:3168)

RE: Coordinate System Problem; Kertau RSO / RSO Malaya (m) (EPSG:3168)

Faiz Nordin — Tue, 14 Jul 2020 07:02:47 GMT

It only happens when I use Malayan projections RSO and GDM2009.

It doesn’t happen when I use it in Cassini projections for every month.

RE: Coordinate System Problem; Kertau RSO / RSO Malaya (m) (EPSG:3168)

Oto — Tue, 14 Jul 2020 05:09:06 GMT

Indeed it looks like it is horizontal shift. Maybe this is issue epsg:3168 "Adopts metric conversion of 0.914398 metres per yard exactly. "

You should contact Bentley to investigate. Is there a shift if using WGS84 coordinates? Does Malaya use GPS shift like China does?

RE: Coordinate System Problem; Kertau RSO / RSO Malaya (m) (EPSG:3168)

Faiz Nordin — Tue, 14 Jul 2020 01:44:56 GMT

Hi Oto,

Refer to the picture above, the distance to the input position is around 118 to 184 meters. I took a photo using DJI Phantom 4 Pro V2, I imported GCP in SRS code EPSG:3168. It is the same thing as above. I think it is not a problem from a DJI device.

RE: Coordinate System Problem; Kertau RSO / RSO Malaya (m) (EPSG:3168)

Oto — Wed, 29 May 2019 07:28:18 GMT

Phantom Pro is lying about GPS altitude. In photo EXIF tags there are no GPS altitudes only barometric altitudes. You can check with exiftool. Rename "exiftool.exe" to "exiftool(-k -a -u -F -n).exe" and check any JPG from P4P you will see that "Absolute altitude" is exactly the same as GPS altitude but it is impossible as absolute altitude comes from absolute barometric pressure and can't align so well. DJI doesn't write GPS altitude for non-RTK Phantoms because it is too innacurate and can change between flights too much.

Flight logs contain real gps values which you can check using log viewer( https://www.phantomhelp.com/LogViewer/Upload/) and export to kml or csv.

Your best option is to adjust altitudes before aerotriangulation. Unfortunately Bentley doesn't try to add any better support for DJI products to correct such issues as it is done by Agisoft or Pix4D.

RE: Coordinate System Problem; Kertau RSO / RSO Malaya (m) (EPSG:3168)

Faiz Nordin — Tue, 28 May 2019 00:57:57 GMT

I used DJI Phantom 4 Pro for mapping, i dont think it GPS fault, maybe the conversion between local coordinate and WGS84 got problems.

RE: Coordinate System Problem; Kertau RSO / RSO Malaya (m) (EPSG:3168)

Oto — Mon, 27 May 2019 05:30:04 GMT

It could be because of wrong GPS altitudes. What device was used to capture photos and from where are positions?