Public Lab Research note

Prototype: filter map tiles in real-time in a browser with ImageSequencer (NDVI Landsat)

by warren | | 585 views | 7 comments |

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I've been working with the new Image Sequencer, a Public Lab project, to try see how it works as a "filter" for map tiles on another site. Working with Mapbox's Landsat Live site, which shows the most recent Landsat satellite images for anywhere on the earth, I created a browser bookmarklet which accepts an Image Sequencer "command string" and runs it on all the tiles currently shown.

This is a great use case for Image Sequencer, a project I've been working on with @ccpandhare and @tech4gt, which is supported in part by NASA's AREN project and by Google Summer of Code.

When you click the bookmarklet, you're prompted for a command string:

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It's a little slow, but I ran the NDVI equation with the command ndvi,colormap (inappropriately, since the imagery shown is just RGB, not infrared, but just as a test) and you can see the results in the lead image and in this video:

Some caveats:

  • it needs some tweaking to "detect" the right layer of tiles to apply to, or it'll apply to the labeling layers too
  • it needs CORS permissions set on the tile server or JavaScript will be denied access to modify the images
  • we haven't yet allowed setting options via the string syntax, but will in this issue and that'll allow things like choosing different color maps
  • we're working on doing the processing on another thread here
  • we could to run the tile processing sequentially because it'd look cool... boop boop boop boop! (the sound of each tile getting converted)

I'm reaching out to MapBox to see if they have infrared bands available, so we can do true NDVI! Any help appreciated!


This is the same kind of filtering we're now enabling in MapKnitter; update on that coming soon:

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@ccpandhare @tech4gt exciting!

@jbreen - you'd know this... are there any tiles available for LANDSAT's near-infrared bands? Especially like NGB type tiles where infrared is in the red channel and visible in the blue? I always ask you these kinds of questions like you're a GIS Gandalf, but it's because you always know!!!

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@wward1400 @adam-griffith @MicheleTobias @lprashad @eustatic @nedhorning @cfastie you might like this little experiment too!

@warren I think you may have stumped me. Have you looked at GloVis?

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@warren wow this looks very promising!! :-D

hunh, can you do this with MODIS?

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Probably! Can you point me at a MODIS source with bands youre interested in?

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@jywarren this is awesome!!! :D

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