As the article said, (the following link is that: https://support.pix4d.com/hc/en-us/articles/202560239#label3) there are three different methods to include GCP for different conditions. here my confuse is that what are the differences among them and if there are some detail explanations of each method. For example, why add and mark GCP with rayCloud after initial processing.
I’ve done the same project using all thee methods and found out that the outputs are almost identical. I usually use method A because it’s the easiest way IMHO to mark GCP’s. All you need to do is find the gcp in raycloud, click on it, mark it on 2 or three images, hit apply and it automatically sorts the images nearest to the GCP for you. Then it’s really easy to mark it on few more images. Do the same on all GCP’s and remember to reoptimze the project and you are ready to process steps 2 and 3
Personally I want to mark them before Step 1 as the picture sorting is just as good to select more pictures (may take a bit longer to get those first couple pictures located so may not be a huge time saver). This saves reprocessing time or at least requires no human interaction in the middle of full processing of all steps.