seprate projection from type for internal use

mapbox · Oct 29, 2018 · 0d4c2ca · 0d4c2ca
1 parent cd3e462
commit 0d4c2ca
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Showing 2 changed files with 43 additions and 21 deletions.
diff --git a/src/geo/mercator_coordinate.js b/src/geo/mercator_coordinate.js
@@ -11,6 +11,31 @@ function circumferenceAtLatitude(latitude: number) {
     return circumference * Math.cos(latitude * Math.PI / 180);
 }
 
+export function mercatorXfromLng(lng: number) {
+    return (180 + lng) / 360;
+}
+
+export function mercatorYfromLat(lat: number) {
+    return (180 - (180 / Math.PI * Math.log(Math.tan(Math.PI / 4 + lat * Math.PI / 360)))) / 360;
+}
+
+export function mercatorZfromAltitude(altitude: number, lat: number) {
+    return altitude / circumferenceAtLatitude(lat);
+}
+
+export function lngFromMercatorX(x: number) {
+    return x * 360 - 180;
+}
+
+export function latFromMercatorY(y: number) {
+    const y2 = 180 - y * 360;
+    return 360 / Math.PI * Math.atan(Math.exp(y2 * Math.PI / 180)) - 90;
+}
+
+export function altitudeFromMercatorZ(z: number, y: number) {
+    return z * circumferenceAtLatitude(latFromMercatorY(y));
+}
+
 /**
  * A `MercatorCoordinate` object represents a projected three dimensional position.
  *
@@ -57,25 +82,24 @@ class MercatorCoordinate {
     static fromLngLat(lngLatLike: LngLatLike, altitude: number = 0) {
         const lngLat = LngLat.convert(lngLatLike);
 
-        const x = (180 + lngLat.lng) / 360;
-        const y = (180 - (180 / Math.PI * Math.log(Math.tan(Math.PI / 4 + lngLat.lat * Math.PI / 360)))) / 360;
-        const z = altitude / circumferenceAtLatitude(lngLat.lat);
-        return new MercatorCoordinate(x, y, z);
+        return new MercatorCoordinate(
+                mercatorXfromLng(lngLat.lng),
+                mercatorYfromLat(lngLat.lat),
+                mercatorZfromAltitude(altitude, lngLat.lat));
     }
 
     /**
      * Returns the `LatLng` for the coordinate.
      *
      * @returns {LngLat} The `LngLat` object.
      * @example
-     * var coord = new mapboxglMercatorCoordinate(0.5, 0.5, 0);
+     * var coord = new mapboxgl.MercatorCoordinate(0.5, 0.5, 0);
      * var latLng = coord.toLatLng(); // LngLat(0, 0)
      */
     toLngLat() {
-        const lng = this.x * 360 - 180;
-        const y2 = 180 - this.y * 360;
-        const lat = 360 / Math.PI * Math.atan(Math.exp(y2 * Math.PI / 180)) - 90;
-        return new LngLat(lng, lat);
+        return new LngLat(
+                lngFromMercatorX(this.x),
+                latFromMercatorY(this.y));
     }
 
     /**
@@ -87,8 +111,7 @@ class MercatorCoordinate {
      * coord.toAltitude(); // 6914.281956295339
      */
     toAltitude() {
-        const lat = this.toLngLat().lat;
-        return this.z * circumferenceAtLatitude(lat);
+        return altitudeFromMercatorZ(this.z, this.y);
     }
 }
 

diff --git a/src/geo/transform.js b/src/geo/transform.js
@@ -2,7 +2,7 @@
 
 import LngLat from './lng_lat';
 import LngLatBounds from './lng_lat_bounds';
-import MercatorCoordinate from './mercator_coordinate';
+import MercatorCoordinate, {mercatorXfromLng, mercatorYfromLat, mercatorZfromAltitude} from './mercator_coordinate';
 import Point from '@mapbox/point-geometry';
 import { wrap, clamp } from '../util/util';
 import {number as interpolate} from '../style-spec/util/interpolate';
@@ -281,8 +281,9 @@ class Transform {
     project(lnglat: LngLat) {
         const lat = clamp(lnglat.lat, -this.maxValidLatitude, this.maxValidLatitude);
         const clamped = new LngLat(lnglat.lng, lat);
-        const coord = MercatorCoordinate.fromLngLat(clamped);
-        return new Point(coord.x * this.worldSize, coord.y * this.worldSize);
+        return new Point(
+                mercatorXfromLng(lnglat.lng) * this.worldSize,
+                mercatorYfromLat(lat) * this.worldSize);
     }
 
     unproject(point: Point): LngLat {
@@ -459,15 +460,15 @@ class Transform {
 
         if (this.latRange) {
             const latRange = this.latRange;
-            minY = this.project(new LngLat(0, latRange[1])).y;
-            maxY = this.project(new LngLat(0, latRange[0])).y;
+            minY = mercatorYfromLat(latRange[1]) * this.worldSize;
+            maxY = mercatorYfromLat(latRange[0]) * this.worldSize;
             sy = maxY - minY < size.y ? size.y / (maxY - minY) : 0;
         }
 
         if (this.lngRange) {
             const lngRange = this.lngRange;
-            minX = this.project(new LngLat(lngRange[0], 0)).x;
-            maxX = this.project(new LngLat(lngRange[1], 0)).x;
+            minX = mercatorXfromLng(lngRange[0]) * this.worldSize;
+            maxX = mercatorXfromLng(lngRange[1]) * this.worldSize;
             sx = maxX - minX < size.x ? size.x / (maxX - minX) : 0;
         }
 
@@ -548,9 +549,7 @@ class Transform {
         this.mercatorMatrix = mat4.scale([], m, [this.worldSize, this.worldSize, this.worldSize]);
 
         // scale vertically to meters per pixel (inverse of ground resolution):
-        // worldSize / (circumferenceOfEarth * cos(lat * π / 180))
-        const verticalScale = this.worldSize / (2 * Math.PI * 6378137 * Math.abs(Math.cos(this.center.lat * (Math.PI / 180))));
-        mat4.scale(m, m, [1, 1, verticalScale, 1]);
+        mat4.scale(m, m, [1, 1, mercatorZfromAltitude(1, this.center.lat) * this.worldSize, 1]);
 
         this.projMatrix = m;