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After georeferencing these 3 images onto my basemap (openstreetmap) they do not line up (see how the white lines are mismatching). Why is this the case and how can I solve this problem?

enter image description here

I made sure that when georeferencing I referenced at least 4 points on the basemap. It seems that the images get compressed or expanded, but I do not see why?

I tried alignment tool in QGIS 3.4.2 but this did not work.


enter image description here

I added transparency the georeferenced images so you can see the problem. Along some streets the images lines up perfectly with the underlying Openstreetmap, but then (in the right hand corner the image gets bend direction southeast and the white line does not align with the underlying street. In the transformation settings I also use WGS 84 – pseudo Mercator (the same CRS as used for the whole project).

  • Did you check the residuals after georeferencing? Did you repeat georeferencing? – Zoltan Jan 25 at 15:12
  • 4 points is likely not enough either, especially if the sources are from varying projection systems. – HeikkiVesanto Jan 25 at 15:18
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    I notice that the off-image is slanted, even leaving a gap on your map. This is often indicative of a projection mismatch between some inputs. – jpmc26 Jan 25 at 20:46
  • I used WGS 84 - pseudo mercator for both the basemap and for the images I want to georeference onto the basemap – Matthias R Jan 27 at 12:00
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They are two possibilities (or maybe more):

  1. The chosen points are too close. ->Choose points in each corner of the image.
  2. You didn't choose the same coordinates system with the three images. ->See the coordinates of the points, if they are too different, the coordinates systems are possibly different too.
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    another possibility is that the images are not orthorectified and have lot of distortion – J.R Jan 25 at 17:32
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If we assume that you have done all the operations correctly, when you are working with Aerial images that cover vast areas you will need more than four points for georeferencing an Image. The underlying algorithm actually treats the Image as a rectangular plane, While in vast areas you are faced with a strongly curved earth. And of course, you have to have the elevation effect in mind.

So, try adding more reference points along all four sides of your image and on the bold features that you have on your base map then the problem will be solved.

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