Use hardcoded values

src/geo/projection/index.js

@@ -30,16 +30,6 @@ const projections = {
     winkelTripel
 };
 
-export function getTransitionToMercatorEndRange() {
-    let maxEndRange = 0;
-    for (const projection in projections) {
-        if (projections[projection].range) {
-            maxEndRange = Math.max(maxEndRange, projections[projection].range[1]);
-        }
-    }
-    return maxEndRange;
-}
-
 export function getProjection(config: ProjectionSpecification) {
     const projection = projections[config.name];
     if (!projection) throw new Error(`Invalid projection name: ${config.name}`);

src/render/draw_sky.js

@@ -20,11 +20,16 @@ import assert from 'assert';
 
 export default drawSky;
 
+const OPACITY_ZOOM_START = 7;
+const OPACITY_ZOOM_END = 8;
+
 function drawSky(painter: Painter, sourceCache: SourceCache, layer: SkyLayer) {
     const tr = painter.transform;
     const isMercator = tr.projection.name === 'mercator';
-    const projectionEndRange = getTransitionToMercatorEndRange();
-    const transitionOpacity = isMercator ? 1.0 : smoothstep(projectionEndRange, projectionEndRange + 1, tr.zoom);
+    // For non-mercator projection, use a forced opacity transition.
+    // This transition is set to be 1.0 after the upper bound which
+    // ensures to be in the mercator projection.
+    const transitionOpacity = isMercator ? 1.0 : smoothstep(OPACITY_ZOOM_START, OPACITY_ZOOM_END, tr.zoom);
     const opacity = layer.paint.get('sky-opacity') * transitionOpacity;
     if (opacity === 0) {
         return;