Derived Terrain Layer :: tilegroxy Docs

Using the Terrain-RGB layer requires a Mapbox access token, supplied through the MAPBOX_KEY environment variable.

Configuration

YAML
JSON

cache:
  name: disk
  path: ./terrain_cache
layers:
  - id: osm
    provider:
      name: proxy
      url: https://tile.openstreetmap.org/{z}/{x}/{y}.png
  - id: air_pressure
    provider:
      name: transform
      threads: 8 (1)
      formula: | (2)
        import "math"
        func transform(r, g, b, a uint8) (uint8, uint8, uint8, uint8) {
          elevation := -10000 + ((float64(r)*256*256 + float64(g)*256 + float64(b)) * 0.1)
          pressure := 101325 * math.Pow(1-.0000225577*elevation, 5.25588)
          c := uint8(pressure / 1000)
          return c, c, c, 255
        }
      provider:
        name: fallback
        primary:
          name: proxy
          url: https://api.mapbox.com/v4/mapbox.terrain-rgb/{z}/{x}/{y}.pngraw?access_token={env.MAPBOX_KEY} (3)
        secondary:
          name: static
          color: "0186a0" (4)
  - id: air_pressure_over_osm
    provider:
      name: blend
      mode: opacity (5)
      opacity: 0.5
      providers:
        - name: ref (6)
          layer: air_pressure
        - name: ref
          layer: osm

1	A tile has 65,536 pixels. Splitting them across 8 goroutines makes each tile faster to produce at the cost of more CPU per request.
2	The function is called once per pixel. Darker pixels are lower pressure, meaning higher ground. See Transform.
3	`{env.MAPBOX_KEY}` keeps the token out of the configuration file. The `pngraw` format matters, as other formats can alter the pixel values and so the decoded elevation.
4	Mapbox returns an error for tiles entirely over the sea. This color decodes to an elevation of 0, so sea level pressure is shown instead of an error.
5	Mixes the two images half and half rather than drawing one over the other, since both layers are fully opaque.
6	Each referenced layer is cached on its own, so `osm` and `air_pressure` can also be requested directly without generating them again.

{
  "cache": {
    "name": "disk",
    "path": "./terrain_cache"
  },
  "layers": [
    {
      "id": "osm",
      "provider": {
        "name": "proxy",
        "url": "https://tile.openstreetmap.org/{z}/{x}/{y}.png"
      }
    },
    {
      "id": "air_pressure",
      "provider": {
        "name": "transform",
        "threads": 8, (1)
        "formula": "import \"math\"\nfunc transform(r, g, b, a uint8) (uint8, uint8, uint8, uint8) {\n  elevation := -10000 + ((float64(r)*256*256 + float64(g)*256 + float64(b)) * 0.1)\n  pressure := 101325 * math.Pow(1-.0000225577*elevation, 5.25588)\n  c := uint8(pressure / 1000)\n  return c, c, c, 255\n}\n", (2)
        "provider": {
          "name": "fallback",
          "primary": {
            "name": "proxy",
            "url": "https://api.mapbox.com/v4/mapbox.terrain-rgb/{z}/{x}/{y}.pngraw?access_token={env.MAPBOX_KEY}" (3)
          },
          "secondary": {
            "name": "static",
            "color": "0186a0" (4)
          }
        }
      }
    },
    {
      "id": "air_pressure_over_osm",
      "provider": {
        "name": "blend",
        "mode": "opacity", (5)
        "opacity": 0.5,
        "providers": [
          {
            "name": "ref", (6)
            "layer": "air_pressure"
          },
          {
            "name": "ref",
            "layer": "osm"
          }
        ]
      }
    }
  ]
}

1	A tile has 65,536 pixels. Splitting them across 8 goroutines makes each tile faster to produce at the cost of more CPU per request.
2	The function is called once per pixel. Darker pixels are lower pressure, meaning higher ground. See Transform.
3	`{env.MAPBOX_KEY}` keeps the token out of the configuration file. The `pngraw` format matters, as other formats can alter the pixel values and so the decoded elevation.
4	Mapbox returns an error for tiles entirely over the sea. This color decodes to an elevation of 0, so sea level pressure is shown instead of an error.
5	Mixes the two images half and half rather than drawing one over the other, since both layers are fully opaque.
6	Each referenced layer is cached on its own, so `osm` and `air_pressure` can also be requested directly without generating them again.

Try it

export MAPBOX_KEY=your-token
tilegroxy test -c terrain.yml
tilegroxy serve -c terrain.yml

The test command confirms all three layers generate before you start the server. Be mindful of the OpenStreetMap tile usage policy.