I'm hoping to generate a new vector file from select points from a raster image in QGIS. I don't know if it is possible.

For instance, I would like to generate a vector point file that puts a point above each of the blue dots in this raster image:

enter image description here

to a vector file with points in the same location as the blue dots in the raster image above - something like this:

enter image description here


1 Answer 1


Quick and dirty, but effective solution:

By the way: you can improve the results if you increase the contrast between points and all other pixels before (in a graphic software). You could create a copy of your input raster with extreme contrasts, just for digitalization purpose, and keep the original for productive use.

  1. Install Magic Wand plugin

  2. Activate the Magic Wand and click on one of the points. A single click creates a polygon layer covering pixels with similar values.

  3. Probably first try does not produce good enough results. Change settings af accuracy and color threshold and click again until all points are covered (maybe zoom in to the pixels of points that are not selected).

  4. With a tiny polygon around each point, run merge vector layers and select all the magic wand layers.

  5. Dissolve the resulting merged polygon layer to get rid of multiple polygons per point.

  6. Convert polygons to points by creating centroids. Be sure to check the box Create centroid for each part.

Result, achieved with a quick try and just a few clicks, based on your screenshot (I guess you have better image quality, thus result will be better). Click a few more times to also create polygons for yet unselected points. Yellow: dissolved polygons; red: centroids = solution you're looking for: enter image description here

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