more raster instructions

Signed-off-by: Ihor Dykhta <[email protected]>

Author: igorDykhta

docs/user-guides/c-types-of-layers/n-raster-tile-layer.md

@@ -5,7 +5,7 @@ Use Raster Tile layer to visualize satellite/aerial imagery from raster pmtiles
 1. Open Add Data → Tilesets.
 2. Select Raster Tile tileset type.
 3. Paste URL to the tileset:
-   - pmtiles (raster format): provide a direct HTTPS URL to a .pmtiles file containing raster imagery.
+   - pmtiles (raster format): provide a direct HTTPS URL to a .pmtiles file containing raster imagery. Raster pmtiles don't require dedicated raster tile servers, unless you want to use elevation meshes.
    - STAC Item/Collection (COGs): provide a HTTPS URL to a STAC Item or Collection (v1.0.0+ with EO + Raster extensions). For this option you need to provide a [compatible raster tile server](https://github.com/igorDykhta/kepler-raster-server).
 4. Click Add.
 5. Style band selection and opacity as needed in Layers panel.
@@ -16,6 +16,14 @@ Important notes for COGs via STAC:
 - COG assets must be publicly accessible over HTTPS.
 - You must run your own raster tile server (e.g., TiTiler). Example implementation that supports collections and elevations: [kepler-raster-server](https://github.com/igorDykhta/kepler-raster-server).
 
+# Elevation
+
+To enable elevation rendering, you must provide one or more compatible raster tile servers when adding the tileset. Enter them in the "Raster tile servers" field of the Add Tileset form.
+
+- For STAC Items/Collections: compatible raster tile servers are required.
+- For raster .pmtiles: raster tile servers are optional for imagery, but required if you plan to use elevation.
+- The server must expose COGs as XYZ tiles and support elevation/DEM tiles. Example implementation: [kepler-raster-server](https://github.com/igorDykhta/kepler-raster-server) (TiTiler-based).
+
 Example Raster .pmtiles:
 
 - Mount Whitney - https://pmtiles.io/usgs-mt-whitney-8-15-webp-512.pmtiles