Forum

Author Topic: Convert CRS of cameras  (Read 2226 times)

AnnaS

  • Newbie
  • *
  • Posts: 24
    • View Profile
Convert CRS of cameras
« on: July 07, 2020, 11:51:57 PM »
Hello,

I have DJI P4P photos in WGS84 (EPSG::4326).

My markers are in NAD83 + NAVD88 + Geoid18. I can't find an undulation grid to import the markers directly into Agisoft, so I need to convert them beforehand. Geoid18 is a relatively new geoid model and thus not many conversion tools support it. The only conversion tool I can find for converting from Geoid18 is the NOAA Vertical Datum Transformation too. However, this only converts to versions of WGS 84, like WGS 84 (G1150) or WGS 84 (G1674). https://vdatum.noaa.gov/vdatumweb/

If I convert the markers to WGS 84 (G1674) and try to bring them into a sparse point cloud set as WGS 84 (EPSG:4326), then I get an error: Unsupported datum transformation.

1) What do you recommend I do? Do you have a recommendation for another coordinate conversion tool?
2) If I change the CRS for the cameras to the converted CRS of the markers before aligning the cameras and importing the markers, I can do this, but the lang/lat/altitude of the cameras don't change as converted coordinates should. How do I correctly change the CRS of the cameras?

Best regards,
Anna

Paulo

  • Hero Member
  • *****
  • Posts: 1303
    • View Profile
Re: Convert CRS of cameras
« Reply #1 on: July 08, 2020, 08:32:39 AM »
Hi Anna,

as remarked in previous post, you can load attached prj file into Select Coordinate System Window to create a compound RS combining NAD83(2011) with NAVD88 Geoid18 Geoid...

For this to work, download the Geoid18.tif file from following link https://drive.google.com/file/d/1ojTwuRaHwDvQlWiZSLKr9T66n8voT1oB/view?usp=sharing and put it into the Geoids folder inside the Metashape installation folder (C:\Program Files\Agisoft\Metashape Pro\geoids)....

Should work...I hope

The transformation from NAD83(2011) to WGS84 (at epoch 2010.0) is defined in TOWGS84 entry of attached prj with geoid18.tif added for final Height...

3rd attachement shows comparison of transformation of same point between Metashape and Vdatum...results are very similar, small differences may be due to interpolation method used or slightly different transformation parameters...
« Last Edit: July 08, 2020, 04:01:27 PM by Paulo »
Best Regards,
Paul Pelletier,
Surveyor

AnnaS

  • Newbie
  • *
  • Posts: 24
    • View Profile
Re: Convert CRS of cameras
« Reply #2 on: July 08, 2020, 05:38:39 PM »
Hi Paulo,

Thanks for the helpful response and repetition.

I requested permission to access the google drive file.

I want to make sure I understand the workflow:
1) Once I have both the geoid tif and prj, create a compound CRS using the Convert tool in the reference pane. Check both cameras and markers in this window.
2) Now cameras will have been converted from WGS84 (EPSG:4326) to NAD83(2011) + NAVD88 Geoid18 height
3) Align photos. Or do I want to convert CRS after aligning photos? As per my second question in my first post of this thread, if I try changing CRS before alignment, the camera long/lat/altitude stay the same.
4) Upload markers as in NAD83(2011) + NAVD88 Geoid18 height.

Paulo

  • Hero Member
  • *****
  • Posts: 1303
    • View Profile
Re: Convert CRS of cameras
« Reply #3 on: July 08, 2020, 05:52:56 PM »
Anna,

that is correct. Only you should:

1. create the Compound CRS by importing or loading prj as I specified in previous. You now have a NAD83(2011) + NAVD88 Geoid18 height CRS.
2. use Convert button to convert your camera positions from WGS84 to newly created CRS ;

from there you can align cameras in this new CRS and import your markers in same CRS to optimize alignment.

Note:  lat/lon will only change from WGS84 to NAD83(2011) + NAVD88 Geoid18 height if your TOWGS84 entry is not set to all 0s. The prj I included does have the entry non zero so you will see a change in lat/lon
« Last Edit: July 08, 2020, 05:57:30 PM by Paulo »
Best Regards,
Paul Pelletier,
Surveyor