check or uncheck images for model and ortho creation with gcps

[Fabien13]

Hello,

I am creating an orthomosaic from drone flight (DJI M300 P1 sensor). I have aligned the images, placed GSPs measured with a DGNSS, and optimized the positions.

To optimize, I unchecked the images and checked the GCPs.
First question: is this the right thing to do in terms of optimization and what to check or uncheck? I understood this from reading this tutorial: https://agisoft.freshdesk.com/support/solutions/articles/31000154132/edit

Second question: for the next steps (building the model and orthomosaic), do I need to check the images again? For now, I've left the images unchecked and the GCPs checked.

Thanks for your help.

Fabien

[Paulo]

Hi Fabien,

I would say to keep them checked if you have PPK or RETK camera positions (cm level accuracy). If not (m level accuracy) tyou can leave unchecked....

[Fabien13]

Thank you, Paulo, for your reply!

My goal is to compare orthomosaics of the same area on different dates.  From a date to another, I'll keep the same coordinates for the GCPs since they do not move.
 
I have an RTK position for my photo and for my GCPs. Coordinates of GCPS are mesured using a DGNSS system that indicates the same default value for the accuracy of all mesured points. It's always 0,012m for y and y (they are merged) and 0.02 for z. The accuracy of the photo coordinates from my M300 is similar or sometimes a slightly better than this but it is still an "inflight position". Gcps, on the other hand, are mesured from ground and their coordinates are an average of several measurements (15). This is why I trust more GCPs than photo coordinates. I don't know how Metashape uses the accuracy data of different sources (GCPs an photo) to ponderate the role of coordinates. 

I think that I need some clarification about Metashape tutorial (the one I mentionned earlier) :

"Generally, it is reasonable to run an optimization procedure based on markers data only. It is due to the fact that GCPs coordinates are measured with significantly higher accuracy compared to GPS data that indicates camera positions. Thus, markers data are sure to give more precise optimization results.


If you want markers to participate in the optimization process, you need to add them to the project and place them on all images, then start the optimization process (for markers to participate, you need to have checkboxes enabled in the Reference pane)."

Does it means that we have to uncheck the photo for the optimisation?

Also the phrase "place them on ALL images" intrigues me. Is it really required to place them on all images?

I'm asking this for the optimization step, but also for the next steps (model and ortho in my case).

Could I get more feedbacks (from Paulo included and from Metashape) about this?  First for the optimisation and next for the other steps.

Thank you, have a good day.

Fabien