mapillary / mapillary/OpenSfM

What is the rationale behind using logarithmic scale within error terms in BA?

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Description

Hello,

I noticed on a few occasions (listed below), a logarithmic scale is used instead of linear. What is the rationale behind this and is it found to be more stable than the linear one?

Also, when these priors/error terms are jointly minimized with reprojection errors, how do you make sure they are not dominated by reprojection errors? For instance, thousands of observations for reprojection errors, with one prior for focal length, or even hundreds for camera poses.

https://github.com/mapillary/OpenSfM/blob/343d1c349a008507f3b7e4be84e31e74c52f92f5/opensfm/src/bundle/error/parameters_errors.h#L7

https://github.com/mapillary/OpenSfM/blob/343d1c349a008507f3b7e4be84e31e74c52f92f5/opensfm/src/bundle/error/parameters_errors.h#L18

https://github.com/mapillary/OpenSfM/blob/ae250d3ebcf7b0a9d589daee8ada3aa68941d5e2/opensfm/src/bundle/error/prior_error.h#L82

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Research direction

Review the linked definitions in opensfm/src/bundle/error/parameters_errors.h and opensfm/src/bundle/error/prior_error.h, starting at the referenced lines. Determine whether the issue calls for documenting the rationale for logarithmic error terms and how their weighting compares with reprojection errors; it is done when those decisions are clearly explained or the question is resolved.

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Assessment

Tech stack
cpp
Domain
computer-vision
Issue type
Documentation
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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