MBTiles: Add ELEVATION_TYPE creation option

Author: drons

doc/source/drivers/raster/mbtiles.rst

@@ -338,6 +338,14 @@ The following creation options are available:
 
          Whether to write the bounds 'metadata' item.
 
+   -  .. oo:: ELEVATION_TYPE
+         :choices: '', 'terrain-rgb'
+         :default: ''
+
+         Type of elevation encoding, suitable for direct generation of
+         Mapbox Terrain-RGB tilesets. See `Mapbox Terrain-RGB v1
+         <https://docs.mapbox.com/data/tilesets/reference/mapbox-terrain-rgb-v1/>`__
+
 -  Vector only:
 
    -  .. co:: MINZOOM

frmts/mbtiles/mbtilesdataset.cpp

@@ -3063,6 +3063,17 @@ bool MBTilesDataset::CreateInternal(const char *pszFilename, int nXSize,
     sqlite3_exec(hDB, pszSQL, nullptr, nullptr, nullptr);
     sqlite3_free(pszSQL);
 
+    const std::string osElevationType = 
+        CSLFetchNameValueDef(papszOptions, "ELEVATION_TYPE", "");
+    if (!osElevationType.empty())
+    {
+        pszSQL = sqlite3_mprintf("INSERT INTO metadata (name, value) VALUES "
+                                 "('elevation_type', '%q')",
+                                 osElevationType.c_str());
+        sqlite3_exec(hDB, pszSQL, nullptr, nullptr, nullptr);
+        sqlite3_free(pszSQL);
+    }
+
     const char *pszTF = CSLFetchNameValue(papszOptions, "TILE_FORMAT");
     if (pszTF)
         m_eTF = GDALGPKGMBTilesGetTileFormat(pszTF);
@@ -3754,6 +3765,11 @@ void GDALRegister_MBTiles()
         "    <Value>overlay</Value>"
         "    <Value>baselayer</Value>"
         "  </Option>"
+        "  <Option name='ELEVATION_TYPE' scope='raster' type='string-select' "
+        "description='Type of elevation encoding' default=''>"
+        "    <Value></Value>"
+        "    <Value>terrain-rgb</Value>"
+        "  </Option>"
         "  <Option name='VERSION' scope='raster' type='string' "
         "description='The version of the tileset, as a plain number' "
         "default='1.1'/>"