Free tool to generate sun/shadow overlays for your hikes (MBTiles for Locus Map)

Hi all,

I made gpxsolar, a free open-source tool (GPLv3) that computes where sun and shadow fall along a GPX track at a given date and time

using elevation data and the terrain horizon — and exports a map overlay you can load directly in Locus Map.

Why it's useful on the trail: on a summer hike you want to know which sections will be in shade at 2 p.m.; in winter, where the sun still reaches; for photography, where the light hits. The overlay shows it at a glance.

Same track, three times of day — the cast shadow moves across the terrain.

How to use it in Locus Map:

1. Load the generated MBTiles as a map overlay (Settings → Maps → overlay).

2. Import the colored track KML as a regular track (the overlay is a raster, so the track comes separately).

3. Keep the overlay opacity at 100 %. The semi-transparency is already baked into the tiles

if you lower Locus's layer opacity, Locus re-composites the tiles and faint seams appear between them. At 100 % it's seamless.

Outputs: KMZ (Google Earth), MBTiles (Locus / OsmAnd overlay), colored track KML. Input is a GPX + a date/time. Runs on Windows / Linux / macOS, GUI or CLI.

Repo (code, build, docs): https://github.com/nico579/gpxsolar

It's a hobby project — feedback very welcome, especially from people who load custom overlays in Locus.