Feature request: define the contour source in a style file

[zstadler]

Please enable defining the contour source in a style file rather than the need to code it in JavaScript.

For example, use this definition in a style file

            contours: {
              type: "contour",
              tiles: [“server.com/{z}/{x}/{y}.png”],
              multiplier: 3.28084,
              thresholds: {
                // zoom: [minor, major]
                11: [200, 1000],
                12: [100, 500],
                13: [100, 500],
                14: [50, 200],
                15: [20, 100],
              },
              elevationKey: "ele",
              levelKey: "level",
              contourLayer: "contours",
              maxzoom: 16,
            },

As the equivalent of this definition in JavaScript:

            contours: {
              type: "vector",
              tiles: [
                demSource.contourProtocolUrl({
                  // meters to feet
                  multiplier: 3.28084,
                  thresholds: {
                    // zoom: [minor, major]
                    11: [200, 1000],
                    12: [100, 500],
                    13: [100, 500],
                    14: [50, 200],
                    15: [20, 100],
                  },
                  elevationKey: "ele",
                  levelKey: "level",
                  contourLayer: "contours",
                }),
              ],
              maxzoom: 16,
            },

Also, is it also possible to define equivalents to DemSource() and sharedDemProtocolUrl that are used in index.html?

==== Note ====
The current alternative is to inline the results of demSource.contourProtocolUrl. For the above example, that would be:

            contours: {
              type: "vector",
              tiles: [
                "dem-contour://{z}/{x}/{y}?buffer=1&contourLayer=contours&elevationKey=ele&extent=4096&levelKey=level&multiplier=3.28084&thresholds=11*250*1000~14*200*800~15*100*400~16*50*200~17*20*100",
              ],
              maxzoom: 16,
            },

This issue is based on this Slack Message

[zstadler]

Also, is it also possible to define equivalents to DemSource() and sharedDemProtocolUrl that are used in index.html?

Perhaps the definition of the contour source could include the name of the DEM source. For example:

          sources: {
            dem: {
              type: "raster-dem",
              encoding: "terrarium",
              tiles: [https://elevation-tiles-prod.s3.amazonaws.com/terrarium/{z}/{x}/{y}.png],
              maxzoom: 13,
              tileSize: 256,
            },
            contours: {
              type: "contour",
              demSource: "dem",
              multiplier: 3.28084,
              thresholds: {
                // zoom: [minor, major]
                11: [200, 1000],
                12: [100, 500],
                13: [100, 500],
                14: [50, 200],
                15: [20, 100],
              },
              elevationKey: "ele",
              levelKey: "level",
              contourLayer: "contours",
              maxzoom: 16,
            },
          },

[msbarry]

Also, is it also possible to define equivalents to DemSource() and sharedDemProtocolUrl that are used in index.html?

Yes, you can just use: "dem-shared://{z}/{x}/{y}"

Perhaps the definition of the contour source could include the name of the DEM source. For example:

I think that config looks great, but it will be a complete rewrite using maplibre's addSourceType API:

https://github.com/maplibre/maplibre-gl-js/blob/a96db2f8ed9ba897eec76042ced0dd045ed9127a/src/ui/map.ts#L2055

It will likely require changes on maplibre side as well since that API is not very well documented and may require changes to maplibre to expose utilities like getting dem tiles from other sources. Overall it should improve things quite a bit though because it will let us run the contour-generation code in maplibre's workers and remove a lot of the code in this plugin for worker coordination, etc.