Terrain-RGB

Terrain-RGB stores one elevation per pixel in the three color channels of an image. This lets elevation tiles be served in ordinary image formats, and clients such as MapLibre compute shading and 3D terrain from them.

Formula

height_m = -10000 + (R · 65536 + G · 256 + B) · 0.1

R is the most significant byte. The value q = R·65536 + G·256 + B lies between 0 and 16,777,215, so the elevation lies between −10,000 m and +1,667,721.5 m in steps of 0.1 m.

Decoding

const hoehe = (r, g, b) => -10000 + (r * 65536 + g * 256 + b) * 0.1;

hoehe = -10000 + (r.astype("uint32") * 65536 + g * 256 + b) * 0.1  # r, g, b als numpy-Arrays

What to watch for

• Read the image format losslessly. mapx serves lossless WebP. Any lossy intermediate step (JPEG, color profile, premultiplied alpha, scaling while decoding) distorts the elevation.
• Do not interpolate before decoding. Blending RGB values does not give a blended elevation. Decode first, then average.
• Mapbox-compatible. encoding: "mapbox" in MapLibre. Terrarium (R·256 + G + B/256 − 32768) is a different encoding and is not served by mapx.
• 512 pixels, no border. tileSize: 512.

Application: DTM terrain model.