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Author Topic: Imported control point coordinates shift away from marker  (Read 701 times)

AnnukkaD

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Imported control point coordinates shift away from marker
« on: June 25, 2020, 01:34:49 PM »
Hi all!

I try to digitize a archaeological site before it will be destroyed under a road work. I've done a dense point cloud, which now should be georeferenced using markers and imported coordinates.

The control point markers are printed from Metashape and the automatic "detect markers" tool works well. The coordinates of the control points are measured with a accurate Trimble positioning system in the ETRS TM35 FIN coordinate system and imported to metashape as ETRS 89. After importing the coordinates the control points shift in the point cloud ca. 5-10 cm away from the marker positions (see image). When measuring a distance in the point cloud, the distance between control points is multiple kilometers, althought it should be some meters. Updating the reference pane does not help. I also tried to transform a few of the control point coordinates to WGS 84 and import them in a clean project file (which had no other coordinates imported) but the points shifted far away from the point cloud.

Any suggestions about what went wrong:

1) The coordinates (a problem during the measurement at site)?
2) The coordinate system I chose for the import? I did not find ETRS TM35FIN in the supported coordinate systems list, which is strange because there are a lot of different national coordinate systems. But ERTS 89 should be the same as ETRS TM35FIN.
3) Some other steps while importing the coordinates? I checked the longitude and latitude columns, so thats not the problem.

Thank you for your help =)

Alexey Pasumansky

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Re: Imported control point coordinates shift away from marker
« Reply #1 on: June 26, 2020, 12:09:01 AM »
Hello AnnukkaD,

I think that the coordinate system is not properly set for the project.

According to the XY values you should use either Local Coordinates option or some projected coordinate system (like UTM projection), however, the selected system is WGS84 and therefore XY values are treated as Longitute and Latitude in degrees.

So please check the coordinate system accordingly via Reference pane settings dialog and then press Update button on the pane's toolbar.
Best regards,
Alexey Pasumansky,
Agisoft LLC

AnnukkaD

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Re: Imported control point coordinates shift away from marker
« Reply #2 on: June 29, 2020, 09:39:02 AM »
Thanks for the help Alexey =)

As solution I now converted the coordinates to WGS 84 and the import works fine