Possible bug or I am not doing something right: Heading line offset on Andoid app

Andrea's Avatar


11 Mar, 2020 04:23 PM

 I noticed in several tests (see attached 2 examples) that the heading line looks to be offset by between -20 to -15 degrees compared to the true direction. The area I tested this is close to Seattle which has a magnetic declination of about +15.5 degrees which is somehow in the range of the offset I see but in opposite sign. Can it be that my phone applies the magnetic declination correction automatically and then the Caltopo app does another correction on top (effectively applying the declination 2 times and therefore the excess in correction?) - or another option is that I am doing (or understanding) something incorrectly. Here the explanation of the tests:
- I placed a marker on the map on a reference feature (e.g a peak) that I could clearly identify and see in the real world
- "started navigation" to that marker from my GPS position
- the app is showing the "true" bearing (e.g. 60 degrees to avalanche mt. in one example)
- then pointed my phone straight at the reference feature making sure there was no magnetic interference (to the best of my knowledge) and calibrating my phone
- the heading line was not passing over the marker which I would have expected to do (e.g. showing a heading of 40 degrees to avalanche mt. in one of the example)

I tried in different locations to make sure that it was not some sort of magnetic interference noticing the the results were consistent. So unless my hands/eyes have a consistent bias that I cannot point the phone correctly and noticing that someone the offset appeared to be "similar" to the declination, I started doubting that it might have been an issue with my understanding or with the app.

Happy to share any additional info/log.
For reference:
 - Device: OnePlus 6T (A6013)
 - Android 10
 - Caltopo App version 0.4.25

  1. Support Staff 1 Posted by matt on 12 Mar, 2020 06:31 PM

    matt's Avatar

    Hi Andrea -

    Thanks for the detailed bug report. I'm a little embarrassed to admit that this is totally on us: we are taking a magnetic bearing from Android and treating it as true (iOS, in contrast, supplies the app with a true bearing).

    My own Android phone does not have a very accurate compass, and so I wasn't able to test with enough precision to pick up on this. It looks like the issue has been in the app for a little while, but we just added the long blue line as a bearing indicator with the last release, which makes the difference far more apparent.

    Really sorry about that.

    • Matt
  2. Ben Lantow closed this discussion on 13 Mar, 2020 02:24 AM.

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