Calculate areas in imagery

AFG
AFG
in Downloading Imagery

I have the world imagery for an area loaded. Trying to work out the area of forestry. I can make the area of trees transparent by selecting the colour and this seems to give a reasonable representation. Is there a way of drawing a polygon around the transparent areas or areas of a selected colour.

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  • DerrickW
    DerrickW
    Answer ✓

    Preemptive disclaimer - I don't think you're going to get great results doing it this way, but I'll show you how to do what you're asking. I assume you actually want to do a land cover classification first, or work off a land cover class layer that's already available to you?


    1. Export your world imagery to a geotiff file first (you don't want to do this off of streaming imagery)
    2. Bring the exported imagery back in to global mapper and close the streaming layer
    image.png


    Adjust match distance as needed

    image.png


    Click "only selected colors", and then "pick color from map". Pick your tree area

    image.png
    image.png
    image.png

    This takes a loooong time to finish and very likely won't produce useful results for you. But if it's close, something you can do is to buffer out the resulting polygons by something like 5 meters, merging polygons as needed. Then, open the attribute table, sort by enclosed area, and delete all of the small polygons created by noise.


    Result: No screenshot, because I'm not going to wait for this to finish..... ;)

Answers

  • AFG
    AFG

    Thanks Derrick,

    Yes I am trying to get landcover classes. The ones available online don't seem to match the vegetation areas when it comes to trees/woodlands. Will give it a go and see what happens.

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