Grassroots Mapping is a series of participatory mapping projects involving communities in cartographic dispute. Seeking to invert the traditional power structure of cartography, the grassroots mappers used helium balloons and kites to loft their own “community satellites” made with inexpensive digital cameras.

Quantify wetland from aerial UV photo

February 24th, 2011 by Cesar Harada

>>Question : How can you extract the % of wetland from an UV aerial picture using photoshop?


Video tutorial by Cesar Harada and Adam Griffith:

_ Instructions :
1. isolate the part that you are interested in using the menu/ image/ adjustment/ replace color. There you want to have a quite fuzzy selection and darken the desired part.
2. after isolating the part you are interested in -black area- apply menu/ image/ adjustment/ threshold
3. use magic wand /untick “contiguous” pixel to select all the black pixels available. Open menu/ window/ histogram/ expanded view. Here you will see how many black pixels are selected. Now you know how many black pixels there is on this image – corresponding the area of wetland from the original UV picture. You can convert the number of pixels into a % (proportions of wetland) or in surface area for quantifying. It is possible to optimize this workflow by creating a script or recording the chain of actions.
Same thread on Public Laboratory

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