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I have a number of images of scanned maps. These maps all fit together in two dimensions. Is there a good tool I can use to specify points common to two overlapping images that'll then scale and align the images? I've tried to do this manually in GIMP but the process is too laborious (and error-prone).

One thing to note is that the images are fairly high resolution bitmaps.

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You can try scantailor. I used it for aligning scanned pictures of books and it has great result. I don't know what do you mean by common points but scantailor can guess common size of pictures and align pictures based on it.

  • By common points, OP probably meant the following: there's a certain overlap between the scanned sections of the map. A common way of aligning images is to analyze the overlapping area in both images, looking for distinctive features and identifying the corresponding pixels in each image. Their location is then used to calculate the correct transformation of one image respective to the other. – user149408 Sep 30 '16 at 19:34
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I suggest you look at Hugin. Hugin is a panorama photo stitching program. Essentially, Hugin is a GUI frontend for Panorama Tools. Stitching is accomplished by using several overlapping photos taken from the same location, and using control points to align and transform the photos so that they can be blended together to form a larger image. Hugin allows for the easy creation of control points between two images, optimization of the image transforms, and much more.

  • That sounds good. Can Hugin do zoom in/out, in case any of the images (maps here, but I'm imagining satellite or aerial photos) aren't the right scale? That probably never happens for panoramic photos where you're supposed to stand still... – Xen2050 Dec 8 '14 at 13:14
  • I have never tried your exact process, so I can't say. I would certainly try it and report back. Hugin is in the Ubuntu repositories. – chili555 Dec 8 '14 at 13:33
  • As far as I know, Hugin can correct rotation as well as for artifacts created by photographic lenses, but I didn't find a way to do any kind of zoom correction. See my questions at photo.stackexchange.com/q/83155/56957 and photo.stackexchange.com/q/83162/56957. – user149408 Sep 30 '16 at 19:39
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Still with Gimp:

With the new Unified transform tool in 2.10:

  • Move the top layer so that one point of reference is above its counterpart in the other layer
  • Drag the transformation center to that point
  • Continue using the tool to scale/rotate the layer to bring the second point over its counter part

With the ofn-layer-aligner script

  • create a path with 4 anchors:
    • two on the two reference points on the reference layer,
    • two on the two matching points in the adjusted layer
  • make the adjusted layer the active layer and call the script, which will move/rotate/scale it so that the two pairs of point overlap.

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