4

When I georeference a raster image in QGIS, it's always a bit displaced as in the attached image (the cyan polygon is the template, the red border is the georeferenced image), although I try to set the georeference points as exact as possible.

Is there a trick to set the georeference points more exact or maybe move the raster layer a bit? Maybe there is a different software, you can georeference by moving and then import it to QGIS?enter image description here

  • 1
    More details please. – mdsumner Jun 29 '14 at 13:17
  • There aren't more details. I need a different way than the georeference tool of QGIS to georeference a raster image, because it produces unprecise results like shown in the attached image. – simskopf Jun 29 '14 at 14:01
  • 3
    For proper georeferencing, you need to add a bunch of reference points, and choose an appropriate method of interpolation. Your picture does not show any points, and we do not know which method you have selected. – AndreJ Jun 29 '14 at 15:33
  • 1
    What kind of reference interpolation did you use(bilinear, nearest neighbor, ...). There might be some improvement here. Besides that ether (1) make more accurate GCP points or just recreate the map in QGIS (doesn't look that complicated) – Curlew Jun 29 '14 at 15:37
  • How many points are you setting to georeference the data and how dispersed are they? I generally find the more points I add (beyond 3 well spaced points) the less accurate the output. – Geezer Jun 29 '14 at 23:42
6

I have good result changing the default transformation settings from Linear to Helmert.

We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

  • 1
    Well, you need to do that if the raster image and the reference data aren't in the same projection. Linear only tries to move the image to the correct location without transforming ("warping") it. – SAnderka Jun 30 '14 at 8:54
  • I took your advice and got a perfect result, thank you :) – simskopf Jun 30 '14 at 9:52
  • 2
    @simskopf: Then you might want to accept Jakob's hint as the correct answer. ;) – SAnderka Jun 30 '14 at 10:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.