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

    npm i --save leaflet.webgl-temperature-map

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:

// 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:

    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

Technical explanation

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.