Merge pull request #75 from cmurphy23/spherical_projection

Project Web Mercator Tiles to Sphere with ShaderMaterial

.gitignore

@@ -7,3 +7,5 @@ pnpm-lock.yaml
 yarn.lock
 
 examples/assets/
+
+.history/

source/nodes/MapNode.ts

@@ -259,21 +259,7 @@ export abstract class MapNode extends Mesh
 		try 
 		{
 			const image: HTMLImageElement = await this.mapView.provider.fetchTile(this.level, this.x, this.y);
-
-			if (this.disposed) 
-			{
-				return;
-			}
-
-			const texture = new Texture(image);
-			texture.generateMipmaps = false;
-			texture.format = RGBAFormat;
-			texture.magFilter = LinearFilter;
-			texture.minFilter = LinearFilter;
-			texture.needsUpdate = true;
-
-			// @ts-ignore
-			this.material.map = texture;
+			await this.applyTexture(image);
 		}
 		catch (e) 
 		{
@@ -292,6 +278,24 @@ export abstract class MapNode extends Mesh
 		this.material.needsUpdate = true;
 	}
 
+	public async applyTexture(image: HTMLImageElement): Promise<void> 
+	{
+		if (this.disposed) 
+		{
+			return;
+		}
+
+		const texture = new Texture(image);
+		texture.generateMipmaps = false;
+		texture.format = RGBAFormat;
+		texture.magFilter = LinearFilter;
+		texture.minFilter = LinearFilter;
+		texture.needsUpdate = true;
+
+		// @ts-ignore
+		this.material.map = texture;
+	}
+
 	/**
 	 * Increment the child loaded counter.
 	 *

source/nodes/MapSphereNode.ts

@@ -1,4 +1,4 @@
-import {Matrix4, BufferGeometry, MeshBasicMaterial, Quaternion, Vector3, Raycaster, Intersection} from 'three';
+import {Matrix4, BufferGeometry, Quaternion, Vector3, Raycaster, Intersection, ShaderMaterial, TextureLoader, Texture, Vector4} from 'three';
 import {MapNode, QuadTreePosition} from './MapNode';
 import {MapSphereNodeGeometry} from '../geometries/MapSphereNodeGeometry';
 import {UnitsUtils} from '../utils/UnitsUtils';
@@ -35,7 +35,50 @@ export class MapSphereNode extends MapNode
 
 	public constructor(parentNode = null, mapView = null, location = QuadTreePosition.root, level = 0, x = 0, y = 0) 
 	{
-		super(parentNode, mapView, location, level, x, y, MapSphereNode.createGeometry(level, x, y), new MeshBasicMaterial({wireframe: false}));
+		let bounds = UnitsUtils.tileBounds(level, x, y);
+
+		// Load shaders
+		const vertexShader = `
+		varying vec3 vPosition;
+
+		void main() {
+			vPosition = position;
+			gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
+		}
+		`;
+
+		const fragmentShader = `
+		#define PI 3.1415926538
+		varying vec3 vPosition;
+		uniform sampler2D uTexture;
+		uniform vec4 webMercatorBounds;
+
+		void main() {
+			// this could also be a constant, but for some reason using a constant causes more visible tile gaps at high zoom
+			float radius = length(vPosition);
+
+			float latitude = asin(vPosition.y / radius);
+			float longitude = atan(-vPosition.z, vPosition.x);
+
+			float web_mercator_x = radius * longitude;
+			float web_mercator_y = radius * log(tan(PI / 4.0 + latitude / 2.0));
+			float y = (web_mercator_y - webMercatorBounds.z) / webMercatorBounds.w;
+			float x = (web_mercator_x - webMercatorBounds.x) / webMercatorBounds.y;
+
+			vec4 color = texture2D(uTexture, vec2(x, y));
+			gl_FragColor = color;
+		}
+		`;
+
+		// Create shader material
+		let vBounds = new Vector4(...bounds);
+		const material = new ShaderMaterial({
+			uniforms: {uTexture: {value: new Texture()}, webMercatorBounds: {value: vBounds}},
+			vertexShader: vertexShader,
+			fragmentShader: fragmentShader
+		});
+
+		super(parentNode, mapView, location, level, x, y, MapSphereNode.createGeometry(level, x, y), material);
 
 		this.applyScaleNode();
 
@@ -67,16 +110,30 @@ export class MapSphereNode extends MapNode
 		const segments = Math.floor(MapSphereNode.segments * (max / (zoom + 1)) / max);
 
 		// X
-		const phiLength = 1 / range * 2 * Math.PI;
-		const phiStart = x * phiLength;
-
+		const lon1 = x > 0 ? UnitsUtils.webMercatorToLongitude(zoom, x) + Math.PI : 0;
+		const lon2 = x < range - 1 ? UnitsUtils.webMercatorToLongitude(zoom, x+1) + Math.PI : 2 * Math.PI;
+		const phiStart = lon1;
+		const phiLength = lon2 - lon1;
+
 		// Y
-		const thetaLength = 1 / range * Math.PI;
-		const thetaStart = y * thetaLength;
-
+		const lat1 = y > 0 ? UnitsUtils.webMercatorToLatitude(zoom, y) : Math.PI / 2;
+		const lat2 = y < range - 1 ? UnitsUtils.webMercatorToLatitude(zoom, y+1) : -Math.PI / 2;
+		const thetaLength = lat1 - lat2;
+		const thetaStart = Math.PI - (lat1 + Math.PI / 2);
+
 		return new MapSphereNodeGeometry(1, segments, segments, phiStart, phiLength, thetaStart, thetaLength);
 	}
 
+	public async applyTexture(image: HTMLImageElement): Promise<void>
+	{		
+		const textureLoader = new TextureLoader();
+		const texture = textureLoader.load(image.src, function() {});
+		// @ts-ignore
+		this.material.uniforms.uTexture.value = texture;
+		// @ts-ignore
+		this.material.uniforms.uTexture.needsUpdate = true;
+	}
+
 	/** 
 	 * Apply scale and offset position to the sphere node geometry.
 	 */

source/utils/UnitsUtils.ts

@@ -38,7 +38,12 @@ export class UnitsUtils
 	public static EARTH_ORIGIN: number = UnitsUtils.EARTH_PERIMETER / 2.0;
 
 	/**
-	 * Converts coordinates from WGS84 Datum to XY in Spherical Mercator EPSG:900913.
+	 * Largest web mercator coordinate value, both X and Y range from negative extent to positive extent
+	 */
+	public static WEB_MERCATOR_MAX_EXTENT: number = 20037508.34;
+
+	/**
+	 * Converts coordinates from WGS84 Datum to XY in Spherical Web Mercator EPSG:900913.
 	 *
 	 * @param latitude - Latitude value in degrees.
 	 * @param longitude - Longitude value in degrees.
@@ -54,7 +59,7 @@ export class UnitsUtils
 	}
 
 	/**
-	 * Converts XY point from Spherical Mercator EPSG:900913 to WGS84 Datum.
+	 * Converts XY point from Spherical Web Mercator EPSG:900913 to WGS84 Datum.
 	 *
 	 * @param x - X coordinate.
 	 * @param y - Y coordinate.
@@ -140,4 +145,59 @@ export class UnitsUtils
 	{
 		return (color.r * 255.0 * 65536.0 + color.g * 255.0 * 256.0 + color.b * 255.0) * 0.1 - 10000.0;
 	}
+
+	/**
+	 * Get the size of a tile in web mercator coordinates
+	 * 	 * 
+	 * @param zoom - the zoom level of the tile
+	 * @returns the size of the tile in web mercator coordinates
+	 */
+	public static getTileSize(zoom: number): number
+	{
+		const maxExtent = UnitsUtils.WEB_MERCATOR_MAX_EXTENT;
+		const numTiles = Math.pow(2, zoom);
+		return 2 * maxExtent / numTiles;	
+	}
+
+	/**
+	 * Get the bounds of a tile in web mercator coordinates
+	 * 	 * 
+	 * @param zoom - the zoom level of the tile
+	 * @param x - the x coordinate of the tile
+	 * @param y - the y coordinate of the tile
+	 * @returns list of bounds - [startX, sizeX, startY, sizeY]
+	 */
+	public static tileBounds(zoom: number, x: number, y: number): number[]
+	{
+		const tileSize = UnitsUtils.getTileSize(zoom);
+		const minX = -UnitsUtils.WEB_MERCATOR_MAX_EXTENT + x * tileSize;
+		const minY = UnitsUtils.WEB_MERCATOR_MAX_EXTENT - (y + 1) * tileSize;
+		return [minX, tileSize, minY, tileSize];
+	}
+
+	/**
+	 * Get the latitude value of a given web mercator coordinate and zoom level
+	 * 
+	 * @param zoom - the zoom level of the coordinate
+	 * @param y - the y web mercator coordinate
+	 * @returns - latitude of coordinate in radians
+	 */
+	public static webMercatorToLatitude(zoom: number, y: number): number 
+	{
+		const yMerc = UnitsUtils.WEB_MERCATOR_MAX_EXTENT - y * UnitsUtils.getTileSize(zoom);
+		return Math.atan(Math.sinh(yMerc / UnitsUtils.EARTH_RADIUS));
+	}
+
+	/**
+	 * Get the latitude value of a given web mercator coordinate and zoom level
+	 * 
+	 * @param zoom - the zoom level of the coordinate
+	 * @param x - the x web mercator coordinate
+	 * @returns - longitude of coordinate in radians
+	 */
+	public static webMercatorToLongitude(zoom: number, x: number): number 
+	{
+		const xMerc = -UnitsUtils.WEB_MERCATOR_MAX_EXTENT + x * UnitsUtils.getTileSize(zoom);
+		return xMerc / UnitsUtils.EARTH_RADIUS;
+	}
 }