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Do I need MTPs when merging subprojects?


I have a large project that I need to split into subprojects (not enough resources to process all at once). I split the project into 7 subprojects and ran step 1 for each. Now, I am trying to create a single project using the other 7 existing projects I created. I got some warnings:

[Warning]: No common tie points or cameras: effective GPS bias rigid transform: scale 1 trans -171 124 -61
[Warning]: RotationMatrix xyz -0 0 -0 opk 3.14159 -0 0
[Warning]: 1 0 0
[Warning]: 0 1 0
[Warning]: 0 0 1

Are manual tie points absolutely necessary? I am unsure how much of a shift I am going to see once I generate some point clouds. Thanks!


It was a good idea of yours to split the dataset into subprojects.

However, what I can advise you is to merge them in the following manner:
The idea is to merge the first subproject with the second using at least 3 MTPs/GCPs. Those MTPs should be marked in each subproject, have the same name and be located in the common area between those two subprojects.

If there aren’t at least 3 MTPs when merging, two or more blocks are created. Therefore, after merging the projects, it is required to add at least 3 MTPs in the common area and Reoptimize in order to obtain a single block.

With the rest of the subprojects, you should proceed accordingly to the graph and the explained manner. It’ll allow you to have control over the accuracy of the project and warning/errors - if you encounter any.


Thanks for responding, Beata. When splitting projects into subprojects via Pix4DMapper, how exactly does the split work? To create MTPS, images have to be reused when subprojects are generated so that I can find like features. Does pix4dmapper use a buffer of sorts when spliting projects into subprojects?

Hi @Adriano_Matos,

There indeed has to be an overlap between subprojects. Therefore, the images at the edge of the common area between subprojects are reused for each one of them during the process.