VISUALIZING TERRAINS WITH CESIUM II

Two years ago we did an experiment with visualizing custom terrains in Cesium (see https://bertt.wordpress.com/2016/12/08/visualizing-terrains-with-cesium/).

At the time, the used command ‘ctb-tile’ did create the ‘heightmap’ format of terrain tiles.  Now there is an updated tool which also creates the ‘quantized-mesh’ format of terrain tiles. The ‘quantized-mesh’ format is more memory efficient and renders faster (because irregular) so let’s experiment with that.

Here more information about the various terrain tile formats and the updated tool https://www.linkedin.com/pulse/fast-cesium-terrain-rendering-new-quantized-mesh-output-alvaro-huarte/

Note for Docker Windows users: in the Docker commands replace ‘$(pwd)’ with a fully specified directory (like ‘d:/gisdata/nederland/terrain’) and double check Docker Settings -> Shared Drives.

Step 1: Download a GeoTIFF file

As example GeoTIFF file we’ll use again a part of Texel in the Netherlands.

$ wget http://www.rijkswaterstaat.nl/apps/geoservices/geodata/dmc/ahn2_05_int/geogegevens/raster/01_09/i09bz1.tif

Step 2: Data preprocessing

It’s recommended to transform tif file to WGS84, so lets do that with gdalwarp.

$ docker run -v $(pwd):/data geodata/gdal gdalwarp -t_srs EPSG:3857 /data/i09bz1.tif /data/i09bz13857.tif

Step 3: create output directory

$ mkdir tiles

Step 4: Run tiling

In this step we run ‘tumgis/ctb-quantized-mesh’, this image adds the -f Mesh option to ctb-tile.

$ docker run -it -v $(pwd):/data tumgis/ctb-quantized-mesh ctb-tile -f Mesh -C -o /data/tiles /data/i09bz13857.tif

Step 5: Create the layer.json file for Cesium

File layer.json is a TileJSON file for  representing map metadata (https://github.com/mapbox/tilejson-spec). Add the ‘-l’ option to create this file.

$ docker run -it -v $(pwd):/data tumgis/ctb-quantized-mesh ctb-tile -l -f Mesh -C -o /data/tiles /data/i09bz13857.tif 

Step 6] Download Cesium 1.51

$ wget https://github.com/AnalyticalGraphicsInc/cesium/releases/download/1.51/Cesium-1.51.zip

Step 7] Unzip Cesium

$ unzip Cesium-1.51.zip -d cesium

Step 8] Edit helloworld

edit ./cesium/Apps/HelloWorld.html in your favorite editor, insert the following script:

Sample code see: https://gist.github.com/bertt/9b4ef34db57f615be369236ace74e543

Step 9: run cesium terrain server

$ docker run -p 9000:8000 -v $(pwd):/data/tilesets/terrain --env WEB_DIR=/data/tilesets/terrain/cesium/ geodata/cesium-terrain-server

Test: The following statement should download 1 terrain tile

$ wget http://localhost:9000/tilesets/tiles/0/0/0.terrain

Step 10: Open browser

Open browser with case-sensitive url http://localhost:9000/Apps/HelloWorld.html

Result should be something like:

Voila, with a few Docker commands we’ve tiled a GeoTIFF image to the new quantised-mesh format and served it up to Cesium.