This example demonstrates how to produce contours from a digital elevation model (DEM) and how to display them with vector tiles.
The approach consists in using the gdal_contour command. Therefore, start by installing gdal:
sudo apt-get install gdal-bin
The geotiff present in this directory comes from the ASTER dataset. If needed, you can now reproject the geotiff in the desired projection (e.g. WebMercator) before importing it in the database.
gdalwarp -rc \ -s_srs epsg:4326 -t_srs epsg:3857 \ -dstnodata 0 -of GTiff -co tiled=yes \ liecthenstein-aster-dem-v2.tif \ liecthenstein-aster-dem-v2-3857.tif
You can now import any GeoTiff DEM as contours in postgis. Here, the -nln argument name the table that contains the data, the -a argument name the column that contains the elevation, the -i argument specifies the interval in meters at which contours are generated.
gdal_contour \ -a elevation -nln aster_dem -i 10 \ -f PostgreSQL \ liecthenstein-aster-dem-v2-3857.tif "PG:host=localhost user=baremaps password=baremaps dbname=baremaps"
The following index can now be created to improve performances. When available, a smoothing function such as ST_ChaikinSmoothing can be used to improve rendering.
DROP INDEX IF EXISTS aster_dem_gix; CREATE INDEX CONCURRENTLY IF NOT EXISTS aster_dem_gix ON aster_dem USING SPGIST(wkb_geometry);
To preview and edit the map in the browser, run the tile server with the following command:
baremaps edit \ --database 'jdbc:postgresql://localhost:5432/baremaps?user=baremaps&password=baremaps' \ --tileset 'tileset.json' \ --style 'style.json'