Point_triangulator: optional intrinsics/extrinsics refinement + refine loop #3589
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WHAT IS DONE?
The intention is to make point_triangulator more useful when starting from approximate poses. It adds three optional flags:
--refine_intrinsics (default 0): refine focal length and extra params (principal point stays fixed).
--refine_extrinsics (default 0): allow pose refinement; otherwise poses are kept fixed.
--refine_loop (default 0): after initial triangulation, run a short loop of global BA → CompleteAndMergeTracks → FilterPoints with early stopping.
WHY IS THIS USEFUL?
Running a standalone bundle adjustment after triangulation does not add/merge tracks using the improved geometry. The refine loop interleaves bundle adjustment with track completion and filtering, which typically yields a cleaner and more complete sparse model without chaining multiple commands.
This could fit the required features in issues like
#3502
#2819
#3433
Meanwhile maintenance is easier than doing a new mode for Colmap CLI
HOW IT WORKS?
Initial triangulation respects refine_extrinsics (fix_existing_frames = !refine_extrinsics).
In the loop, poses are optimized only if --refine_extrinsics=1; otherwise a bundle adjustment is run with all poses kept constant.
Defaults preserve current behavior (no loop, poses fixed), so it doesn't break compatibility at all!