add marker tries to find something intersecting the projection ray that passes through the pixel and something else (mesh, dem, dense cloud) if that occurs, the marker will be created on the 3D space with source coordinates filled taken from the aforementioned source item.
place marker new, just creates one marker projection in the current photo (2D) source coordinates remain empty. The marker will become apparent in the 3D space once that you (or the program on its own means) place another projection of same marker on a different photo. but still the marker remains with empty source coordinates.
to align unreferenced chunk to a referenced one by markers shared between the two, you don't need source coordinates, so you can use whatever type of marker. what you should not allow it it to have "source" marker coordinates on the non-referenced chunk while having the marker checked in ref pane list (otherwise they would be in conflict with destination coordinates)
Regards,
Geobit
Accupixel
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