Leaflet.WebglTemperatureMap

A simple and fast Leaflet Library to draw temperature maps (heat maps) using WebGL in pure Javascript. Except a O(N) pre-process step which is done in Javascipt, all calculations and drawing are done with shaders in WebGL, so it is pretty fast.

Inspired by temperature-map-gl

Triangulation of mask powered by earcut

In plans rewrite hole package to pixi or three.js (or may be pts) from naked webGL

Demo

- Temperature map demo →
- Temperature map with transparent background demo →

Basic Usage

``shell script
npm i --save leaflet.webgl-temperature-map
`

`js
import L from 'leaflet';
import 'leaflet.webgl-temprature-map';

const map = L.map(); // creates map

const tempMap = L.webGlTemperatureMapLayer().addTo(map);

tempMap.setPoints([
[2630.0850293955414, 7132.896936250415, 64.16567943765965],
[4065.465306828053, 600.8491068712285, 41.28007958055719],
[4559.413280590601, 6877.027363962465, 30.497164030229907]
]);
`

points are in this format:

`js
// x, y - can be lat lng (must set second param in setPoints as { isLatLng: true}), or screen coords
const points = [[x0, y0, v0], [x1, y1, v1], ...[xN, yN, vN]];
`

Requirements

- Leaflet ^1.5.0
- Leaflet-geometryutil ^0.9.1

Reference

#### L.webGlTemperatureMapLayer(options)

Return Object of class

#### Options

- All options from Leaflet setOptions
- idwOptions - options to temperature map: {
- p: 5,
- canvas: null,
- zIndex: 10,
- opacity: 0.35,
- range_factor: 0.00390625,
- gamma: 2.2,
- debug_points: false, // work only for debug - not right position on zoom after move
- framebuffer_factor: 1,
- isNullColorized: true, // to transparent background set false
- point_text:
`function(val) {
let v;
if (val < 1) v = val.toFixed(2);
else if (val < 10) v = val.toFixed(1);
else v = Math.round(val);
return v;
}
``
}

#### Methods

- onAdd(map): Sets temperature map to leaflet map.
- setPoints(points: [x, y, value], options: { isLatLng: false }): Adds array of points to the temperature map and draws it. X, y - can be lat lng, or screen coords.
- needRedraw(): Redraws the temperature map.

#### Callbacks

- **onDrawLayer({
layer,
canvas,
bounds,
size,
zoom,
center,
ce,
ce_b,
corner
})**: Call when layer did redraw.
- onLayerWillUnmount(): Call when layer will unmount.
- onLayerDidMount(): Call when layer did mount.

Changelog

#### 0.1.0 — July 05, 2020

- Fix default options

#### 0.1.0 — July 05, 2020

- Add options to temperature map.
- Add ability to set background transparent
- Add ability to set points as lat,lng or L.Point

#### 0.0.1 — May 06, 2020

- Initial release.

License

MIT License

$3

Values are calculated using 'Inverse Distance Weighting (IDW)' algorithm:

Wikipedia - Inverse Distance Weighting

The rest of the explanation makes sense only in the context of the wikipedia article above...

For every point, we perform a render pass to a texture. Using IDW, we calculate the point "influence" to every fragment using a fragment shader. We store the ui\*wi at the r channel of the texture and w_i at the g channel. Using blending with "accumulator" configuration, we end end up with a texture, where we have the top sum of IDW in r channel, and the bottom sum at the g channel. Since channels WebGL are clamped in [0,1], we multiply both channels with range_factor to avoid clamping.

At last, we perform a last pass where we get the IDW value by reading the calculation texture and do a r/g at every fragment. We then use this value to determine the color of the fragment.