OpenTopoMap icon indicating copy to clipboard operation
OpenTopoMap copied to clipboard

Published 20 hours ago • verified publisher icon der-stefan

Garmin: lines are wrong and weird

Open sikmir opened this issue 1 year ago • 2 comments

On the first screen is OTM slippy map, on the second screen is OTM Garmin map. Why all lines on Garmin map are "twisted"?

  • I've tried to view the map on Garmin device as well - the same result.
  • I've even tried to build Garmin map from source (following instruction) - again, the same wierd result.

scr

sikmir avatar Sep 16 '22 16:09 sikmir

As far as I know garmin format coordinate precision is quite low - all vertexes are snapped to a grid.

tomass avatar Sep 17 '22 17:09 tomass

As far as I know garmin format coordinate precision is quite low - all vertexes are snapped to a grid.

Wow, didn't know that! I'm really surprised.

sikmir avatar Sep 17 '22 17:09 sikmir

mkgmap can only produce maps in a format that is more than 20 years old which is limited to 24b per coordinate. All modern GARMIN maps are using the NT format (in fact it is not a format but rather an exponential state space of special cases - NT stands for an recursive acronym: "NT is Not a formaT") which uses up to 32b per coordinate, that's why modern GARMIN maps look ok while all OSM maps generated with mkgmap/cgpsmapper look broken.

tumic0 avatar Sep 20 '22 14:09 tumic0