Leaflet.Multispectral

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

It is available as a node module as leaflet-multispectral.

Also see Leaflet.TileFilter, which is a re-implementation of this library for on-the-fly TileLayer filtering.

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

Usage

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

// create an image
var img = L.imageOverlay('example.jpg', [[29.0, -118.2],[29.1, -118.4]]);

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

img.addTo(map);

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

img.revert();

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

img.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

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

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