Measure Tool reverses Magnetic Variation when crossing 180 Meridian
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Assessment
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Newbie friendliness
- 55/100
Research direction
Start by locating the Measure tool’s magnetic-variation calculation and how it handles longitude across the 180th meridian; the issue does not name source files or tests. Reproduce the behavior by measuring across the meridian in both directions, then verify the magnetic variation remains consistent.
Written by the indexing model from the issue text.
Description
Describe the bug
When using the Measure tool, if the start point is in the eastern hemisphere and the measure line is pulled to the western hemisphere, the magnetic variation is incorrectly calculated (added instead of subtracted, for example) when the line crosses the 180th meridian. This occurs whether going E to W or W to E.
To Reproduce
See above
Expected behavior
Variation should be consistent
Screenshots
See video. Watch the Magnetic direction change.
https://github.com/user-attachments/assets/9139bba4-998c-4c50-ae08-04a05cbcf70d
Desktop (please complete the following information if applicable):
Edition Windows 11 Home
Version 25H2
Installed on 10/17/2025
OS build 26200.8457
- Dominant language
- C
- Stars
- 1.5k
- Forks
- 627
- Avg merge
- 1d 9m
- Merged PRs (30d)
- 9
Getting set up
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First steps
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- Open a pull request that references the issue number.
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