setTerrain is accepted but the ground stays flat

• map.setTerrain({ source: 'terrain', exaggeration: 1.5 }) runs, yet setPitch(55) still shows a flat plane.
• Error: Source "terrain" cannot be used as terrain because it is not a raster-dem source.
• fill-extrusion buildings stand on a flat base instead of following the slope.

1. Print map.getSource('terrain').type and map.getTerrain().
2. Check the declared encoding against the DEM producer, terrarium versus mapbox.
3. Download one DEM tile and check whether it is 256x256 or 512x512.
4. Check maxzoom against the current zoom and whether the view is tilted at all.

Declare type: 'raster-dem' with encoding 'terrarium', tileSize matching the tiles, minzoom 0 and maxzoom 12, then setTerrain with exaggeration 1.5 and setPitch(55) so relief becomes visible.

Error: Source "terrain" cannot be used as terrain because it is not a raster-dem source.

var src = map.getSource('terrain');
console.log('源类型', src.type);
console.log('地形配置', map.getTerrain());
map.on('error', function (e) { console.error(e.error && e.error.message); });

• Raising exaggeration from 1.5 to 10 to make mountains appear amplifies wrong decoding into spikes.
• Setting tileSize: 512 for 256-pixel tiles interpolates elevations incorrectly and flattens the terrain.