Handle arcgis vector-tile services tilemap

[JohnAtle]

Some arcgis vector-tile services uses a "vector tilemap" to define what tiles exist in the tilgrid. See https://developers.arcgis.com/rest/services-reference/enterprise/vector-tilemap.htm and https://developers.arcgis.com/rest/services-reference/enterprise/tile-map.htm

When requesting tiles not defined in the tilemap, we get a "204 - No content" in response, and a blank tile is shown in the map.

A workaround is to define a setTileLoadFunction that when getting a 204 response, will do a request on the above zoom-levels until a tile is found and use this. See https://codesandbox.io/s/blank-arcgis-vector-tiles-workaround-3v5xnz

I would request either (in prioritized order):

• update OpenLayers code to use and handle "vector tilemap" similar as ArcGIS Maps SDK for JavaScript
• update OpenLayers code to add logic to request from above zoom-levels when getting a 204 response for a vector tile
• add an example in the examples section about how to handle 204 responses for vector tile requests the correct way

[ottarv]

Excellent suggestion and nice workaround. Note that 404 - Not found should be treated the same as 204 - No content when requesting vector tiles from arcgis.

[rdewit]

FWIW, if you have control over the generation of the vector tile package, setting the 'Tiling Format' to 'Flat' (as opposed to 'Indexed', which is the default), the availability of the tiles will be predictable, i.e. there should not be any gaps in the tile availability. And the 'Index Polygons' setting may need to be blank (not sure about that).

@JohnAtle , I noticed that the layer you point to in your workaround has absolute paths to the sprites, glyphs and tiles. Most other ArcGIS tile services use relative paths, which are not supported directly by openlayers or maplibre-gl. Do you know how to configure these services to use absolute paths?

[JohnAtle]

@rdewit Thanks for the information about the 'Tiling Format', that is very interesting. Unfortunately I do not have any control over the ArcGIS services so I can not change this. (I have never set up an ArcGIS service, so I am sorry I can not help with the use of absolute path.)