SRS with DJI cameras and GCPs

RE: SRS with DJI cameras and GCPs

Oto — Mon, 09 Sep 2019 12:07:44 GMT

Same question for me. It is very strange indeed as it pops only for a moment.

RE: SRS with DJI cameras and GCPs

Riccardo Corbari — Mon, 09 Sep 2019 11:59:39 GMT

Thanks Oto. One last question: for report purposes, do you know where I can check the reference altitude set just after importing the photos in ContextCapture? The Block does not show the setting anymore.

Thanks.

RE: SRS with DJI cameras and GCPs

Oto — Mon, 09 Sep 2019 09:34:55 GMT

It also depends on SRS as for some XY are used interchanged. Also you seem to be confused by SRS which are shown in viewer it is only readout and it doesn't mean that it is in this SRS as you can read coordinates and do measurements in any SRS. As I said internally Contextcapture uses ECEF so coordinates are only set in import or export(production) it is not possible to switch them at any other step, when importing they are translated to ECEF.

RE: SRS with DJI cameras and GCPs

Riccardo Corbari — Mon, 09 Sep 2019 08:41:34 GMT

I solved, finally, setting a different SRS on GCPs and Reconstructions/Productions. Don't miss to receive the correct references by the surveyor.

RE: SRS with DJI cameras and GCPs

Riccardo Corbari — Sat, 07 Sep 2019 14:33:00 GMT

One more question: can I reference the GCPs in Editor? I still cannot produce a model with the same references supplied by the surveyor.

RE: SRS with DJI cameras and GCPs

Riccardo Corbari — Sat, 07 Sep 2019 09:07:49 GMT

Another update.

Running a first AT with altitude set to WGS ellipsoid and also adding GCPs in WGS84, returned an AT upside down (photo positions lower on Z axis, and splats above).

Since the surveyor gave us orthographic coordinates based on IGM95, is it possible that - instead - we must use geographic coordinates, assuming we're producing a 3D model?

RE: SRS with DJI cameras and GCPs

Riccardo Corbari — Fri, 06 Sep 2019 17:16:12 GMT

Update: CC just finished a brand new AT, started in a new project made for the same acquisition.

The pose metadata of the images, before the AT was WGS84 - EGM96 geoid. After AT, it has been changed to WGS84 - EPSG:4326.

Is this because of AT adjusting?

RE: SRS with DJI cameras and GCPs

Riccardo Corbari — Fri, 06 Sep 2019 16:12:14 GMT

[quote userid="5932" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/185159/srs-with-dji-cameras-and-gcps/542543"]

SRS should be set for each import correctly for photos if GPS is used it automatically uses WGS84 and for importing GCPs you manually set SRS+vertical system. If GCPs are used then photo altitudes are not critical.

If Survey points are in WGS then it is ok it means it uses ellipsoid height and not geoid

[/quote]

Thanks Oto. About this quote and importing GCPs, when you say to set SRS+vertical system, do you mean WGS84 only? Since it should assume that the altitude is based on ellipsoid. Please let me know, thanks.

Meanwhile I'm running a new project with new AT, where I changed the added photos altitude to WGS instead of MSL.

RE: SRS with DJI cameras and GCPs

Oto — Fri, 06 Sep 2019 11:31:09 GMT

After importing photos there is a warning shown in status bar that for last photos WGS84 with MSL is used and you can click on this warning and it will allow to change to WGS84 ellipsoid. For P4 it is calculated altitude by absolute barometric pressure as it equals same value as one from barometric altitude, in older firmwares it was GPS but also way off..

If Survey points are in WGS then it is ok it means it uses ellipsoid height and not geoid, geoids can be added by "vertical system override"

RE: SRS with DJI cameras and GCPs

Riccardo Corbari — Fri, 06 Sep 2019 09:31:44 GMT

[quote userid="5932" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/185159/srs-with-dji-cameras-and-gcps/542444"]DJI P4 doesn't write GPS altitudes in EXIF, it writes barometric altitude[/quote]

Thanks Oto for your prompt reply. I do not understand this above: what matters if DJI writes baro altitudes, if I add to my AT and production the GCPs which indicate surveyed points? All the 3D model should be oriented, scaled and placed at the altitude as per GCPs. Is it correct? Also, in our case the altiture on EXIF does not appear to be barometric, please look at the following screenshot:

[quote userid="5932" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/185159/srs-with-dji-cameras-and-gcps/542444"]choose WGS84 ellipsoid[/quote]

Do you mean to change pose metadata of the images to WGS84? (without indicating UTM or geoid)

[quote userid="5932" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/185159/srs-with-dji-cameras-and-gcps/542444"]But it doesn't matter if GCPs are used if they are in correct SRS.[/quote]

SRS shouldn't be set when adding GCPs? The wizard asks for the SRS when we add GCPs.

[quote userid="5932" url="~/products/3d_imaging_and_point_cloud_software/f/contextcapture-descartes-pointools-forum/185159/srs-with-dji-cameras-and-gcps/542444"]Keep in mind there are 2 SRS needed for horizontal and vertical directions. What geoid does the survey points use?[/quote]

I thank you so much for this information, I wasn't aware of this. But I don't understand why CC requires 2 SRSs: where can I set them? How they are managed, since the GCPs are added with just one SRS? The survey points do not use any geoid, they've been registered in WGS84 and converted to orthogonal points by Leica CS20. As an example, one of the survey points report data like this:

POINT_NAME,520307.644,5041300.019,131.713

So reference coordinates are in meters.

I will also look more in deep into ECEF, thanks.

RE: SRS with DJI cameras and GCPs

Oto — Fri, 06 Sep 2019 05:52:51 GMT

It is not so much bug of CC regarding altitudes but fact that DJI P4 doesn't write GPS altitudes in EXIF, it writes barometric altitude so it doesn't matter which geoid is used but it seems more accurate after adding photos is to choose WGS84 ellipsoid(just keep in mind that it will set it as default for next imports, very strange GUI approach). But it doesn't matter if GCPs are used if they are in correct SRS. Keep in mind there are 2 SRS needed for horizontal and vertical directions. What geoid does the survey points use?

Also there is no need to mess with coordinates and trying to change before aerotriangulation. Contextcapture anyway internally uses ECEF coordinates so it recalculates them from any coordinate system to ECEF for displaying together.