maplibre-gl
Version:
BSD licensed community fork of mapbox-gl, a WebGL interactive maps library
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text/typescript
import {RGBAImage} from '../util/image';
import {warnOnce} from '../util/util';
import {register} from '../util/web_worker_transfer';
/**
* The possible DEM encoding types
*/
export type DEMEncoding = 'mapbox' | 'terrarium' | 'custom'
/**
* DEMData is a data structure for decoding, backfilling, and storing elevation data for processing in the hillshade shaders
* data can be populated either from a pngraw image tile or from serialized data sent back from a worker. When data is initially
* loaded from a image tile, we decode the pixel values using the appropriate decoding formula, but we store the
* elevation data as an Int32 value. we add 65536 (2^16) to eliminate negative values and enable the use of
* integer overflow when creating the texture used in the hillshadePrepare step.
*
* DEMData also handles the backfilling of data from a tile's neighboring tiles. This is necessary because we use a pixel's 8
* surrounding pixel values to compute the slope at that pixel, and we cannot accurately calculate the slope at pixels on a
* tile's edge without backfilling from neighboring tiles.
*/
export class DEMData {
uid: string | number;
data: Uint32Array;
stride: number;
dim: number;
min: number;
max: number;
redFactor: number;
greenFactor: number;
blueFactor: number;
baseShift: number;
/**
* Constructs a `DEMData` object
* @param uid - the tile's unique id
* @param data - RGBAImage data has uniform 1px padding on all sides: square tile edge size defines stride
// and dim is calculated as stride - 2.
* @param encoding - the encoding type of the data
* @param redFactor - the red channel factor used to unpack the data, used for `custom` encoding only
* @param greenFactor - the green channel factor used to unpack the data, used for `custom` encoding only
* @param blueFactor - the blue channel factor used to unpack the data, used for `custom` encoding only
* @param baseShift - the base shift used to unpack the data, used for `custom` encoding only
*/
constructor(uid: string | number, data: RGBAImage | ImageData, encoding: DEMEncoding, redFactor = 1.0, greenFactor = 1.0, blueFactor = 1.0, baseShift = 0.0) {
this.uid = uid;
if (data.height !== data.width) throw new RangeError('DEM tiles must be square');
if (encoding && !['mapbox', 'terrarium', 'custom'].includes(encoding)) {
warnOnce(`"${encoding}" is not a valid encoding type. Valid types include "mapbox", "terrarium" and "custom".`);
return;
}
this.stride = data.height;
const dim = this.dim = data.height - 2;
this.data = new Uint32Array(data.data.buffer);
switch (encoding) {
case 'terrarium':
// unpacking formula for mapzen terrarium:
// https://aws.amazon.com/public-datasets/terrain/
this.redFactor = 256.0;
this.greenFactor = 1.0;
this.blueFactor = 1.0 / 256.0;
this.baseShift = 32768.0;
break;
case 'custom':
this.redFactor = redFactor;
this.greenFactor = greenFactor;
this.blueFactor = blueFactor;
this.baseShift = baseShift;
break;
case 'mapbox':
default:
// unpacking formula for mapbox.terrain-rgb:
// https://www.mapbox.com/help/access-elevation-data/#mapbox-terrain-rgb
this.redFactor = 6553.6;
this.greenFactor = 25.6;
this.blueFactor = 0.1;
this.baseShift = 10000.0;
break;
}
// in order to avoid flashing seams between tiles, here we are initially populating a 1px border of pixels around the image
// with the data of the nearest pixel from the image. this data is eventually replaced when the tile's neighboring
// tiles are loaded and the accurate data can be backfilled using DEMData#backfillBorder
for (let x = 0; x < dim; x++) {
// left vertical border
this.data[this._idx(-1, x)] = this.data[this._idx(0, x)];
// right vertical border
this.data[this._idx(dim, x)] = this.data[this._idx(dim - 1, x)];
// left horizontal border
this.data[this._idx(x, -1)] = this.data[this._idx(x, 0)];
// right horizontal border
this.data[this._idx(x, dim)] = this.data[this._idx(x, dim - 1)];
}
// corners
this.data[this._idx(-1, -1)] = this.data[this._idx(0, 0)];
this.data[this._idx(dim, -1)] = this.data[this._idx(dim - 1, 0)];
this.data[this._idx(-1, dim)] = this.data[this._idx(0, dim - 1)];
this.data[this._idx(dim, dim)] = this.data[this._idx(dim - 1, dim - 1)];
// calculate min/max values
this.min = Number.MAX_SAFE_INTEGER;
this.max = Number.MIN_SAFE_INTEGER;
for (let x = 0; x < dim; x++) {
for (let y = 0; y < dim; y++) {
const ele = this.get(x, y);
if (ele > this.max) this.max = ele;
if (ele < this.min) this.min = ele;
}
}
}
get(x: number, y: number) {
const pixels = new Uint8Array(this.data.buffer);
const index = this._idx(x, y) * 4;
return this.unpack(pixels[index], pixels[index + 1], pixels[index + 2]);
}
getUnpackVector() {
return [this.redFactor, this.greenFactor, this.blueFactor, this.baseShift];
}
_idx(x: number, y: number) {
if (x < -1 || x >= this.dim + 1 || y < -1 || y >= this.dim + 1) throw new RangeError('out of range source coordinates for DEM data');
return (y + 1) * this.stride + (x + 1);
}
unpack(r: number, g: number, b: number) {
return (r * this.redFactor + g * this.greenFactor + b * this.blueFactor - this.baseShift);
}
getPixels() {
return new RGBAImage({width: this.stride, height: this.stride}, new Uint8Array(this.data.buffer));
}
backfillBorder(borderTile: DEMData, dx: number, dy: number) {
if (this.dim !== borderTile.dim) throw new Error('dem dimension mismatch');
let xMin = dx * this.dim,
xMax = dx * this.dim + this.dim,
yMin = dy * this.dim,
yMax = dy * this.dim + this.dim;
switch (dx) {
case -1:
xMin = xMax - 1;
break;
case 1:
xMax = xMin + 1;
break;
}
switch (dy) {
case -1:
yMin = yMax - 1;
break;
case 1:
yMax = yMin + 1;
break;
}
const ox = -dx * this.dim;
const oy = -dy * this.dim;
for (let y = yMin; y < yMax; y++) {
for (let x = xMin; x < xMax; x++) {
this.data[this._idx(x, y)] = borderTile.data[this._idx(x + ox, y + oy)];
}
}
}
}
register('DEMData', DEMData);