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GPS Accuracy and Pix4D catch

I have been field testing Pix4Dcatch on an iPad 2020 Pro. My experience has been mixed. When using it as a standalone app the program works well. It is able to capture the necessary overlap for close proximity to the point of interest. I would rate the cloud as doing an average job of making a model.

I prefer to use the license and use the desktop Pix4dmapper to fine-tune my models. MTPs go a long way in helping keep models together.

One of my goals to achieve with the catch app would be to use the Pix4Dcapture app to take overhead shots to get the top of structures and a good orthomap area and use catch app to fill in the gaps of the sides of the structure. While both programs work well on there own on I had issues with trying to combine the two together. After running step 1 and getting my ATPs I saw a strange output. After spinning around the model what had happened was the DJI Phantom 4 pro and iPad Pro 2020 had two different sets of GPS readings. While the two were close (within 30 feet) it was off too much for MTPs.

Side note, I did not use GCPs and have not field-tested this option to see if it will correct the GPS issues. Also, the DJI coordinates were spot on. It was the iPad that had misleading GPS data.


The accuracy of the GPS data for Pix4Dcatch is unfortunately limited to the accuracy of device. We do currently sample the reported GPS accuracy throughout the duration of the capture and use the best result we get, but there’s a good chance the drone could get a better signal or even have a better GPS receiver.

GCPs should correct the issue, otherwise It might help to let the iPad have time to acquire a good GPS signal before starting capture.


George Brown

Could you please help clarify my understanding on GCPs?

Question, if GPS coordinates from the iPad are within an error margin and all GPS coordinates of images are accurate relative to themselves within that project would GCPs correct the ATPs back to the correct point?

Hopefully I explained my question well. If not, I can show an example.