MGA2020 in Victoria (AUS) transformation problems

RE: MGA2020 in Victoria (AUS) transformation problems

Oto — Thu, 02 Dec 2021 08:26:01 GMT

[quote userid="1187895" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems/684945"]there is no option to change projections (for position)[/quote]

Of course there is no other option as it uses JPG tags and that only has options for altitude reference.

[quote userid="1187895" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems/684945"]My question here is, if I can get results with MGA94, adopt the exact workflow, except with MGA2020, why isn't CC applying the shift? [/quote]

To apply geoid difference Contextcapture needs both geoids.

[quote userid="1187895" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems/684945"]How can the transformation work for one projection and not the other?[/quote]

7 parameter transformation is low accuracy(~1 meter) usable in GIS softwares. Try to set WGS84 in QGIS and import same control points in both systmes in QGIS and see if it does transformation correctly.
You need to provide grid shift files for better accuracy.

In what coordinate system you input control points?

RE: MGA2020 in Victoria (AUS) transformation problems

James Livesey — Wed, 01 Dec 2021 00:49:50 GMT

Hi Oto, thanks for the reply.

[quote userid="5932" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems/684942"]

James Livesey said:
The P4 RTK Drone collects all the data in WGS84, there is no setting to change projections.

Not entirely true. After importing photos you need to set that photos altitude is from WGS84 ellipsoid and not sea level. It can be only set once after import and then this lost . This setting is still undocumented.

[/quote]

Yes, I am aware of this setting in realtion to altitude. I was refering to the actual DJI setting on the controller, there is no option to change projections (for position)

[quote userid="5932" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems/684942"]

James Livesey said:
CC isn’t recognising the GDA2020 transformation from WGS84 to GDA2020

Seems 7 parameter affine transformation is not supported. I also tried affine ABRIDGEDTRANSFORMATION parameter but no luck. Even that CC uses GDAL libraries same WKT definition which works in QGIS doesn't work in CC. But PROJ4 Helmert towgs84 parameter worked.

[/quote]

My question here is, if I can get results with MGA94, adopt the exact workflow, except with MGA2020, why isn't CC applying the shift?

How can the transformation work for one projection and not the other?

RE: MGA2020 in Victoria (AUS) transformation problems

Oto — Wed, 01 Dec 2021 00:17:43 GMT

[quote userid="1187895" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems"] The P4 RTK Drone collects all the data in WGS84, there is no setting to change projections.[/quote]

[quote userid="1187895" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems"]CC isn’t recognising the GDA2020 transformation from WGS84 to GDA2020[/quote]

There is also this idea which now has status planned - Add custom affine transformation to projected | Reality Modeling Ideas (aha.io)

[quote userid="1187895" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/222831/mga2020-in-victoria-aus-transformation-problems"]vert overrides excel sheets in the gdal folder (as advised by Bentley)[/quote]

Advised but I would not reccomend. Better add each GTX in separate WKT definition as this way at least you will have more control and each Contextcapture update will not overwrite the edited csv and less alarming error if model is opened on other computer which doesn't have correct GTX.

Sounds suspicous why you are exchanging GTX files? You need to create additional vertical systems if needed. If you jut overwrite one GTX with other then of course it won't work correcty as CC doesn't care about geoid names.