Translations using 1 GCP

[rhys]

Hi,

I have a P4RTK that I am using to capture survey data and process in Pix4D. The base station is positioned using a “here” shot, meaning a horizontal and vertical translation is required to bring the work into terms of the local coordinate system. I know what the translation parameters will be, and they are in the order of 1.3m horizontally and around 30m vertically.

It is written above that horizontal grid corrections are not currently supported. What are the implications of using the RTK accurate EXIF position data from the photos to get the model to process, then use just one GCP to translate the data horizontally and vertically?
Is this the best way to handle the translation issue?

Thanks

Rhys

[Blaz]

Hi @rhys,

In general, we recommend a minimum of 3 GCPs to georeference the project. However, I understand that you are using a DJI Phantom 4 RTK that has precise image geolocation, and you would just like to shift the project to the correct location.

Theoretically, it should be possible to use only one GCP but I am not saying this is the recommended way to approach the situation.

The best would be if you place a mininum of 3 GCPs or that you do transform the image geolocation in the output coordinate system as mentioned here:

UK-British national grid-coordinate system

Hello everyone, I’m using a Phantom 4 RTK to do topographic drone surveys on construction sites. I have a inquiry about the best way to process a survey information in Pix4D using the OSGB 1936 British National Grid. At the moment, I use Grid InQuest II to transform the GeoTiff coordinates from ETRS89 Geodetic to OSGB36/ British National Grid (Tn15/GM15) and add the transformation of the x, y, z to Pix4D for the input coordinate system and for output I select the OSGB 1936 for x, y coordina…

I hope this helps,

[rhys]

Thanks for the reply,

Further to this question. When I introduce GCP’s to the project, what geolocation information takes precedence. In other words, does the inclusion of 3 GCPS mean that Pix4d ignores the RTK solution on the images?

I am trialing including GCPs, but changing their use to a checkpoint not a 3d GCP. This way the GCP is acting as an independent check on the RTK positioned images, but not affecting the solution from Pix4D.

Thanks again.

Rhys

[Blaz]

Both image geolocation and orientation are taken into account when processing. So if you have RTK geotags, they will be used for processing.

However, if there is a shift between image geolocation and the position of the GCPs, then the position of GCPs will be used to shift the project to its final position. In this sense, GCPs have a bit more weight.

Best,