Garmin: lines are wrong and weird

der-stefan / OpenTopoMap

A topographic map from OpenStreetMap and SRTM data

https://opentopomap.org

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Garmin: lines are wrong and weird #328

Closed sikmir closed 1 year ago

sikmir commented 2 years ago

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

tomass commented 2 years ago

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

sikmir commented 2 years ago

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.

tumic0 commented 2 years ago

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.