jsfreemaplib/demtiler.js

Miscellaneous JavaScript classes and functions for working with geodata, including working with Spherical Mercator projection and managing XYZ tiles, plus some general UI functions.

// from aframe-osm-3d - added to jsfreemaplib 0.3.x
const Tiler = require('./Tiler');
const PNG = require('pngjs').PNG;
const DEM = require('./DEM');

class DemTiler extends Tiler {

    constructor(url) {
        super(url);
        this.allDems = { };
    }

    async readTile(url) {
        return new Promise ( (resolve, reject) => {
            const arrbuf = fetch(url).then(res => res.arrayBuffer()).then
                (arrbuf => {
                    const png = new PNG();
                
                    png.parse(arrbuf, (err, data) => {
                        if(err) reject(err);
                        let i;
                        const elevs = [];
                        for(let y = 0; y < png.height; y++) {
                            for(let x = 0; x < png.width; x++) {
                                i = (y * png.width + x) << 2;
                                elevs.push(Math.round((png.data[i] * 256 + png.data[i+1] + png.data[i+2] / 256) - 32768));
                            }
                        }
                        resolve( { w: png.width,
                                   h: png.height,
                                   elevs: elevs } );

                    });
                });
            }); 
    }

    // New in 0.4.3, allows lookup of elevation for arbitrary points
    getElevation(sphMercPos) {
        const tile = this.getTile(sphMercPos, this.tile.z);
        const indexedTile = this.indexedTiles[`${tile.z}/${tile.x}/${tile.y}`];
        if(indexedTile) {
            return indexedTile.getHeight(sphMercPos[0], sphMercPos[1]);
        }
        return Number.NEGATIVE_INFINITY;
    }

    getElevationFromLonLat(lon, lat) {
        return this.getElevation(this.sphMerc.project(lon, lat));
    }

    // Overridden to store each tile as a DEM object
    _rawTileToStoredTile(tile, data) {
         const topRight = tile.getTopRight();
         const bottomLeft = tile.getBottomLeft();
         const xSpacing = (topRight[0] - bottomLeft[0]) / (data.w-1);
         const ySpacing = (topRight[1] - bottomLeft[1]) / (data.h-1);
         const dem = new DEM (data.elevs, 
                            bottomLeft, 
                            data.w,
                            data.h, 
                            xSpacing, 
                            ySpacing);
        return dem;
    }
}

module.exports = DemTiler;