Sideload offline packs

[kylebarron]

It looks like sideloading offline packs might get supported in react-native-mapbox-gl (https://github.com/react-native-mapbox-gl/maps/pull/588).

Building mbgl-offline

mbgl-offline is the CLI to assemble offline databases for side-loading.

https://github.com/mapbox/mapbox-gl-native/wiki/Sideloading-offline-maps

These worked for me:

1. Clone the Maps SDK: git clone https://github.com/mapbox/mapbox-gl-native.git
2. Change to the root folder: cd mapbox-gl-native
3. Check out the release commit equivalent to the version of the Maps SDK that you are using: git checkout {commit hash} (view all release commits)
4. Compile the binary: make offline
   Once the build is complete, you'll see the message Build Succeeded in the terminal. The binary is available under the build folder (for example, on a Mac the file will be in build/macos/Debug/mbgl-offline).

Creating the offline pack

To create the offline pack:

./mbgl-offline \
    --geojson buffer.geojson \
    -o offline.db \
    --style=https://raw.githubusercontent.com/nst-guide/osm-liberty-topo/gh-pages/style-png.json \
    --minZoom=0 \
    --maxZoom=14

A 2 mile buffer around Sec A is 19MB. This includes contours and terrain but not NAIP.

When I run with --style=https://raw.githubusercontent.com/nst-guide/osm-liberty-topo/gh-pages/style-hybrid-png.json, that gives a 48MB db. So here the NAIP imagery (up to zoom 14) is 30MB for the 2 mile buffer.

Note that --geojson must be a single geometry. If you pass a FeatureCollectino it won't work. In this case, buffer.geojson is a 2-mile buffer around Sec A as a top-level type=Polygon.

It looks like it correctly intersects the polygon with xyz boxes, instead of just taking the bounding box of the provided geometry.

To get the xyz tiles downloaded for a given pack:

sqlite3 offline.db 'SELECT x,y,z from TILES;'

(offline.db is just a Sqlite3 database)

Then if you want to turn those xyz coords into a GeoJSON describing the tiles' geometry:

1. Use a text editor to convert 1|2|3 to [1, 2, 3] (surely possible with sed but haven't tried)
2. run

cat db_tiles.txt | mercantile shapes | fio collect > db_tiles_Z14.geojson

where db_tiles.txt has

Here's a visualization of the tiles used for this:

[kylebarron]

surely possible with sed but haven't tried)

I think I did this recently with awk. Specifically here:

https://github.com/nst-guide/data in the tiles docs