Ground Control Points Issue

[ChelseaMorgan]

When I try to perform the bundle adjustment to scale the model with the control points I get the error message "Not enough tie points during minimization. Try to increase the re-projection error or to decrease the constraints variance". What does this mean and how can I fix it? I've attached a picture of my setup before I select "OK". I'm a new user and would appreciate any help.
Thanks,
Chelsea

[Andrea Alessi]

Hi Chelsea,

I realized you asked me via email and i forgot to reply to this question, my apologies.

It means that the minimization failed due to not enough tie points able to reach the target reprojection error. You can click "show advanced settings" in the "bundle adjustment" if you wish to increase re-projection error.

If you are not interested in doing an additional bundle adjustment but you wish to simply scale the model, you can simply uncheck "perform bundle adjustment".

If you also have more control points available, I also suggest you don't use all your control points as constraints but use some of them as constraints and some of them as control only.

[ChelseaMorgan]

What purpose does the additional bundle adjustment serve? If I only scale the model will it decrease the geospatial accuracy of my model and resulting orthomosaic?

Thanks,
Chelsea

[Andrea Alessi]

Hi Chelsea,

The bundle adjustment is a non linear minimization procedure that adjust points and cameras by minimizing the reprojection error of points. An additional BA is advised especially when you need accuracy, however while it is true that the minimum amount of control points is 3, having only 4 will probably not be very influential unless the initial reconstruction is very wrong. I would aim to have a few more control points (also consider having some as control only rather than constraint)

You can find a tutorial here and a video tutorial here