function to only set elevation if center point is below horizon

Author: NathanMOlson

src/geo/projection/globe_transform.ts

@@ -111,6 +111,9 @@ export class GlobeTransform implements ITransform {
     setMinElevationForCurrentTile(elevation: number): void {
         this._helper.setMinElevationForCurrentTile(elevation);
     }
+    setElevationIfCenterPointBelowHorizon(elevation: number): void {
+        this._helper.setElevationIfCenterPointBelowHorizon(elevation);
+    }
     setPadding(padding: PaddingOptions): void {
         this._helper.setPadding(padding);
     }

src/geo/projection/mercator_transform.ts

@@ -86,6 +86,9 @@ export class MercatorTransform implements ITransform {
     setMinElevationForCurrentTile(elevation: number): void {
         this._helper.setMinElevationForCurrentTile(elevation);
     }
+    setElevationIfCenterPointBelowHorizon(elevation: number): void {
+        this._helper.setElevationIfCenterPointBelowHorizon(elevation);
+    }
     setPadding(padding: PaddingOptions): void {
         this._helper.setPadding(padding);
     }

src/geo/transform_helper.ts

@@ -190,6 +190,12 @@ export class TransformHelper implements ITransformGetters {
         this._minElevationForCurrentTile = ele;
     }
 
+    setElevationIfCenterPointBelowHorizon(elevation: number): void {
+        if (this.pitch <= 89.0) {
+            this.setElevation(elevation);
+        }
+    }
+
     get tileSize(): number { return this._tileSize; }
     get tileZoom(): number { return this._tileZoom; }
     get scale(): number { return this._scale; }

src/geo/transform_interface.ts

@@ -177,6 +177,15 @@ interface ITransformMutators {
     setCenter(center: LngLat): void;
     setElevation(elevation: number): void;
     setMinElevationForCurrentTile(elevation: number): void;
+
+    /**
+     * Sets the transform's center elevation above sea level, in meters.
+     * Only takes effect if the current center point is below the horizon.
+     * If the current center point is above the horizon, setting the elevation to ground level will cause
+     * the camera to move belo the map.
+     */
+    setElevationIfCenterPointBelowHorizon(elevation: number): void;
+
     setPadding(padding: PaddingOptions): void;
 
     /**

src/ui/map.ts

@@ -2031,9 +2031,7 @@ export class Map extends Camera {
             if (this.painter.renderToTexture) this.painter.renderToTexture.destruct();
             this.painter.renderToTexture = null;
             this.transform.setMinElevationForCurrentTile(0);
-            if (this.transform.pitch <= 89) {
-                this.transform.setElevation(0);
-            }
+            this.transform.setElevationIfCenterPointBelowHorizon(0);
         } else {
             // add terrain
             const sourceCache = this.style.sourceCaches[options.source];
@@ -2057,9 +2055,7 @@ export class Map extends Camera {
                 } else if (e.dataType === 'source' && e.tile) {
                     if (e.sourceId === options.source && !this._elevationFreeze) {
                         this.transform.setMinElevationForCurrentTile(this.terrain.getMinTileElevationForLngLatZoom(this.transform.center, this.transform.tileZoom));
-                        if (this.transform.pitch <= 89) {
-                            this.transform.setElevation(this.terrain.getElevationForLngLatZoom(this.transform.center, this.transform.tileZoom));
-                        }
+                        this.transform.setElevationIfCenterPointBelowHorizon(this.terrain.getElevationForLngLatZoom(this.transform.center, this.transform.tileZoom));
                     }
                     this.terrain.sourceCache.freeRtt(e.tile.tileID);
                 }
@@ -3205,14 +3201,12 @@ export class Map extends Camera {
         if (this.terrain) {
             this.terrain.sourceCache.update(this.transform, this.terrain);
             this.transform.setMinElevationForCurrentTile(this.terrain.getMinTileElevationForLngLatZoom(this.transform.center, this.transform.tileZoom));
-            if (!this._elevationFreeze && this.transform.pitch <= 89) {
-                this.transform.setElevation(this.terrain.getElevationForLngLatZoom(this.transform.center, this.transform.tileZoom));
+            if (!this._elevationFreeze) {
+                this.transform.setElevationIfCenterPointBelowHorizon(this.terrain.getElevationForLngLatZoom(this.transform.center, this.transform.tileZoom));
             }
         } else {
             this.transform.setMinElevationForCurrentTile(0);
-            if (this.transform.pitch <= 89) {
-                this.transform.setElevation(0);
-            }
+            this.transform.setElevationIfCenterPointBelowHorizon(0);
         }
 
         this._placementDirty = this.style && this.style._updatePlacement(this.transform, this.showCollisionBoxes, fadeDuration, this._crossSourceCollisions, transformUpdateResult.forcePlacementUpdate);