dem2terrainrgb

This module is to convert DEM to terrain RGB raster tiles.

Installation

cd dem2terrainrgb
pipenv install

Usage

$ python main.py -h
usage: dem2terrainrgb.py --dem {dem file path} --dist {output directory path} --tmp {temporary directory path} --webp --remove_png --zoom {min-max zoom}

This module is to convert DEM to terrain RGB raster tiles.

optional arguments:
  -h, --help    show this help message and exit
  --dem DEM     Original DEM file. It must be already reprojected to EPSG:3857 before converting.
  --dist DIST   Output directory for tiles
  --tmp TMP     Temporary work directory
  --webp        Use this option if you want to convert PNG to webp tiles
  --remove_png  Use '--webp' option together. If this option is used, it will remove all of original PNG tiles.
  --zoom ZOOM   Specify min-max zoom level for tiles. Default is 5-15.

The below is an example command. Before executing this module, you must reproject your DEM to EPSG:3857 coordinates by using GDAL or QGIS.

pipenv shell
python main.py --dem ./data/rwanda_dem_EPSG3857_10m.tif --dist ./tiles --webp --zoom 5-15

Finally, you can delete all of xml files under tiles folder.

find ./tiles -name "*.xml" -exec bash -c 'rm "$1"' - '{}' \;

Validation

If you want to validate processed tiff image, you can command like below.

$ rio info --indent 2 ./data/rwanda_dem_EPSG3857_10m_without_nodata.tif

{
  "blockxsize": 256,
  "blockysize": 256,
  "bounds": [
    3223733.0877,
    -316437.17616185057,
    3439718.7685284764,
    -115768.6321
  ],
  "colorinterp": [
    "gray"
  ],
  "compress": "deflate",
  "count": 1,
  "crs": "EPSG:3857",
  "descriptions": [
    null
  ],
  "driver": "GTiff",
  "dtype": "uint16",
  "height": 19992,
  "indexes": [
    1
  ],
  "interleave": "band",
  "lnglat": [
    29.92940323722318,
    -1.9409140983431143
  ],
  "mask_flags": [
    [
      "all_valid"
    ]
  ],
  "nodata": null,
  "res": [
    10.037442179964515,
    10.037442179964515
  ],
  "shape": [
    19992,
    21518
  ],
  "tiled": true,
  "transform": [
    10.037442179964515,
    0.0,
    3223733.0877,
    0.0,
    -10.037442179964515,
    -115768.6321,
    0.0,
    0.0,
    1.0
  ],
  "units": [
    null
  ],
  "width": 21518
}

For verifying the elevation data, you may do the below command.

$ gdallocationinfo -wgs84 ./data/rwanda_dem_EPSG3857_10m_RGB.tif 29.7363 -2.2313
Report:
  Location: (8617P,13218L)
  Band 1:
    Value: 1
  Band 2:
    Value: 199
  Band 3:
    Value: 250
(rwanda_terrain)

Formula is like this:

height = -10000 + ((R * 256 * 256 + G * 256 + B) * 0.1)

Convert to MBTiles

You can use mb-util module to convert tilesets into a mbtiles container.

$ mb-util --image_format=png --scheme=xyz ./tiles/ ./tilesets/rwanda_dem_EPSG3857_10m.mbtiles

If you want to create mbtiles from webp tiles, the command should be like below.

$ mb-util --image_format=webp --scheme=xyz ./tiles/ ./tilesets/rwanda_dem_EPSG3857_10m_webp.mbtiles

Before running mb-util, don't forget to put metadata.json under tiles folder. The below is an example of content for metadata.json.

{
  "name": "Rwanda 10m Terrain RGB Tileset",
  "description": "Rwanda 10m Terrain RGB Tileset, CC-BY-4.0: Water and Sanitation Corporation (WASAC), Rwanda",
  "version": "1"
}

Tile hosting

You can upload tilesets to Github pages for hosting. If you would like to host tiles on your own server, you may be able to use mbtilesserver.

After installing mbtileserver,

~/go/bin/mbtileserver --verbose

it will automatically find mbtiles under tilesets folder, then access to http://localhost:8000/services. You will see the following response.

[
    {
        "imageType": "png",
        "url": "http://localhost:8000/services/rwanda_dem_EPSG3857_10m",
        "name": "Rwanda 10m Terrain RGB Tileset"
    }
]

After that, continue to access http://localhost:8000/services/rwanda_dem_EPSG3857_10m and see more detailed information.

{
    "description": "Rwanda 10m Terrain RGB Tileset, CC-BY-4.0: Water and Sanitation Corporation (WASAC), Rwanda",
    "format": "png",
    "map": "http://localhost:8000/services/rwanda_dem_EPSG3857_10m/map",
    "maxzoom": 15,
    "minzoom": 5,
    "name": "Rwanda 10m Terrain RGB Tileset",
    "scheme": "xyz",
    "tilejson": "2.1.0",
    "tiles": [
        "http://localhost:8000/services/rwanda_dem_EPSG3857_10m/tiles/{z}/{x}/{y}.png"
    ],
    "version": "1"
}

Tileset URL will be as below.