I am wondering if there is a way to use the RTK data from the drone (.ubx files) instead of using GCP’s. If so, how accurate is the output?
There is an article which explains the expected accuracy for Pix4D outputs here.
There is a way to use RTK data from the drone. This information has to be supplied in a supported format. A list of supported format here.
In case, you are using RTK coordinates, it is also very important to assign the correct accuracy when importing the geotags. The default values are 5 and 10 m but RTK accuracy should be set to a few centimeters.