[style-spec] client-side hill-shading source/layer/properties

[mollymerp]

As we prepare to add a new layer type for rendering hill-shading on the client using a tiled DEM, we need to discuss the associated style-spec properties that will need to be added.

The plan right now is to initially release the hill-shading functionality using the terrain-rgb raster tiles as the source.

The properties in @kkaefer's original implementation using encoded DEM in a vector tile feature he added the following properties:

terrain-shadow-color: The color of the terrain that faces away from the light source.
terrain-highlight-color: The color of the terrain that faces towards the light source.
terrain-accent-color: The color used to accentuate rugged terrain with sharp cliffs and gorges.
terrain-illumination-direction: Direction of the light source. Defaults to top left.
terrain-illumination-alignment: Direction of the light source when the map is rotated. viewport or map
terrain-exaggeration: Intensity of the terrain

Now that we have a global light I imagine the last three can be replaced with the global light properties.

Opening this ticket to start discussing naming and additional properties we may need. @andrewharvey has suggested we call this layer type hillshade and save the terrain layer type for use with 3d mesh terrain (feature request #1489 )

cc @mapbox/gl @mapbox/cartography-cats

[ajashton]

call this layer type hillshade and save the terrain layer type for use with 3d mesh terrain

+1 to "hillshade". FWIW our current use of "terrain" (as in "Mapbox Terrain") refers to the combination of elevation (incl. hillshade) and landcover information.

[1ec5]

Now that we have a global light I imagine the last three can be replaced with the global light properties.

That would be ideal. It’s difficult enough for a developer using the runtime styling API to visualize the light object’s position value; finding an appropriate corresponding value for terrain-illumination-* would be even more frustrating.

Should light object’s color value also influence the hillshading colors too?

terrain-exaggeration: Intensity of the terrain

Could this exaggeration be expressed in relation to some real-world unit? What is the default value, and how would we describe its effect on the hillshading?

[kkaefer]

+1 to "hillshade"

I used "terrain" intentionally because it's more than "just" hillshading in that it includes openness. However, I can see that "terrain" is too broad and overloaded, so I'd be okay with "hillshade" even if it doesn't tell the whole story.

[andrewharvey]

This has been done in #5286