Applying custom Geoid

Shannon_Valley1 · September 27, 2019, 1:58pm

Hi Everyone.

Is it possible to apply custom geoid to Pix4D? I have Phantom IV RTK and I want to apply OSGM15 geoid (UK+Ireland), as I’m having systematic vertical difference (vs handheld GPS RTK coordinates) when applying predefined geoid EGM2008 (before appying GCP). I think with RTK accuracy I shouldn’t have that problem with proper geoid applied.

Have TIF file with OSGM15 definition, but doesn’t work, when put to folder with other geoids.

Many thanks.

Przemek

Pix4D_Alumni_TE · August 21, 2019, 7:18pm

Hi,

Yes, it is possible to use a custom geoid, but there are a few rules to take into consideration:

Pix4D does not support the use of local geoid models yet, so the conversion to the desired local geoid has to be performed before importing the dataset into Pix4Dmapper. Transforming the vertical coordinate system of the RTK dataset (and GCPs, if it is the case) is applied by using an external tool provided, for example, by the national mapping institute.
A constant height and a global geoid could also be used although the accuracy will be lower. If you use the constant height, you will likely obtain inaccuracies, because it is not 100% certain that the elevation of the dataset has a constant offset compared with the geoid of reference.

For more information about vertical systems in Pix4Dmapper, please read the article

https://support.pix4d.com/hc/en-us/articles/360021076212-How-to-define-Pix4D-outputs-with-respect-to-a-Geoid-model

Cheers,

Teodora

Shannon_Valley1 · August 20, 2019, 6:07pm

Teodora,

Thank you, I tried all above before, just wanted to know, if there is a shortcut by applying custom geoid. Helpful when flying over difficult areas, where no GCPs can be installed.

Found a way around it anyway, just takes little bit more time.

Reg.

Przemek

Pix4D_Alumni_TE · August 20, 2019, 6:07pm

Hi,

Unfortunately, there is no shortcut at the moment. Currently, Pix4Dmapper lets you choose from the geoids EGM 84, EGM 96 and EGM 2008. Converting to other geoids has to be performed beforehand, with 3rd party tools.

It is nice to hear you found a workaround. However, Pix4D is constantly improving and adding new functionalities, in order to optimize the processing and analysis of 3D data.

Cheers,

Teodora

rpas2 · November 5, 2020, 3:49am

Will it be possible to upload a user geoid file to Pix4D Mapper? Or can Pix4D look to load more geoids into the next version? We are currently using NZVD16 which I now see is supported by Pix4Dmatic, so it appears that this can be done?

Beata · November 5, 2020, 8:42am

Hi @rpas2,

Indeed, in Pix4Dmatic, it is possible. However, in Pix4Dmapper it won’t be. Instead, you could select the option Arbitrary Coordinate System for the outputs and the GCPs and import GCPs with coordinates in the coordinate system you specified. In this case, the software will respect the GCPs values and will try to fit the model as good as possible to the GCPs. Then, all your outputs will still be in an arbitrary reference system, but this system will be based on the system defined by the GCPs.

Regards