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publiclab / leaflet-tile-filter

Multispectral color manipulation and processing (NDVI etc) for Leaflet tile layers with pure JavaScript in Image Sequencer
https://publiclab.github.io/leaflet-tile-filter/
GNU General Public License v3.0
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Leaflet.TileFilter

This Leaflet plugin provides multispectral channel manipulation and processing tools (such as NDVI or other remote sensing methods) for Leaflet tile layers using pure client-side JavaScript. It uses image-sequencer and was developed by Public Lab.

It is based on the simpler plugin for ImageOverlays at https://github.com/publiclab/leaflet-multispectral

It is available as a node module as leaflet-tile-filter.

demo.png

This library was made possible in part by NASA's AREN project.

Usage

See the demo for basic usage: https://publiclab.github.io/leaflet-tile-filter/

// create an tile layer
var tileLayer = L.tileLayer(
  'https://gibs-{s}.earthdata.nasa.gov/wmts/epsg3857/best/' +
  '{layer}/default/{time}/{tileMatrixSet}/{z}/{y}/{x}.jpg',
  {
    layer: 'MODIS_Terra_CorrectedReflectance_Bands721',
    tileMatrixSet: 'GoogleMapsCompatible_Level9',
    maxZoom: 9,
    time: '2013-11-04',
    tileSize: 256,
    subdomains: 'abc',
    noWrap: true,
    continuousWorld: true,
    // Prevent Leaflet from retrieving non-existent tiles on the
    // borders.
    bounds: [
      [-85.0511287776, -179.999999975],
      [85.0511287776, 179.999999975]
    ],
    attribution:
      '<a href="https://wiki.earthdata.nasa.gov/display/GIBS">' +
      'NASA EOSDIS GIBS</a>&nbsp;&nbsp;&nbsp;' +
      '<a href="https://github.com/nasa-gibs/web-examples/blob/master/examples/leaflet/webmercator-epsg3857.js">' +
      'View Source' +
      '</a>'
});

// apply a colormap:
tileLayer.filter('colormap');

tileLayer.addTo(map);

To revert the image to it's previous state, use:

tileLayer.revert();

Multi-step commands

With a small change coming in Image Sequencer, multi-step commands and the full Image Sequencer syntax will be available:

// apply NDVI equation to the image, and then a colormap:
tileLayer.filter('ndvi,colormap');

For more complex commands, you can use JavaScript expresssions, in the following format:

tileLayer.filter('dynamic{red:R*2|green:B|blue:B/2}');

In this example, we're using Image Sequencer's dynamic module to set the displayed RGB values individually, with the expressions R*2, B, and B/2, respectively.

Image Sequencer

(coming soon) Commands you can pass into the filter are extremely flexible; they are Image Sequencer string syntax (full object notation coming soon). Read about Image Sequencer and how to use it here:

https://github.com/publiclab/image-sequencer

Using the visual editor, you can develop a command string to pass into this filter:

https://sequencer.publiclab.org

Image Sequencer is implemented in pure JavaScript, and is under development; we expect optimizations as well as worker threads and WebAssembly to improve performance in upcoming versions.

About Multispectral imagery

Learn about multi-band imagery, some of it's uses at this great blog post by Charlie Lloyd of Mapbox:

https://blog.mapbox.com/putting-landsat-8s-bands-to-work-631c4029e9d1

Here's some sources of Landsat 8 data:

Here's more on NDVI and DIY techniques to collect multi-band imagery: https://publiclab.org/infragram

Multispectral TMS tile sources

Additional multi-band imagery