1

I'm working with a raster map that looks like this:

map

Do you know any way to select the red/blue spots or ideally put a points on them? I've been browsing web and qgis help for a while now, but I haven't found anything useful as of yet.

3

Sometimes I face similar issues, though I do need to get polygons from the images. My current solution is as follows:

  1. Use the info tool to get the specific RGB values of the areas of interest
  2. Use the raster calculator to change the value of all areas of interest to 1 while the rest of the image is 0 (e.g. image@1=255 AND image@2=167 - this gives all pixels with RGB 255,167,xxx out as 1 while the rest becomes 0).
  3. Use the contour dialogue to convert the black-and-white image to contourlines.
  4. Convert the contour lines to polygons
  5. In your case: Get the centroids of the polygons.

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