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I have a non-georeferenced vector layer that I need to be georeferenced. With raster layers the task is easy and straightforward, but I have no idea what should I do with my vector layer. I have a few control points with known coordinates which should provide some basis to transformation. So, let's say I know points with id-s of 1, 2 and 3 should have the coordinates of x1,y1 ; x2,y2 ; x3,y3. There might be some rotation and scale transformation in addition to simple shifting. Any ideas?

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Have you tried the qgsAffine plugin? Similar question here: gis.stackexchange.com/questions/22691/how-to-georeference-a-dxf – Rayner Sep 11 '12 at 11:25
The Affine plug-in will probably do the transformation, but you will need to know the transformation parameters to use it. Can you post the vector coordinates and the corresponding real-world coordinates for your three points? N. – nhopton Sep 11 '12 at 11:38
Can you convert the shapefile to a tiff using gdal_rasterize, georeference the tiff, then extract the parameters from the world file? – klewis Sep 11 '12 at 20:55

4 Answers

up vote 4 down vote

To georeference a vector layer, try the qgsAffine plugin. More info here: Where to find qgsaffine in the menu?

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Thank you for answers. I guess I have to use the qgsAffine then and figure out the transofrmation parameters manually. I was just hoping that there's some way to automate that process. Perhaps I'll try writing some Python code to do that – AHaav Sep 11 '12 at 11:46
Thinking about it, you might find that GRASS v.transform (it's in the Sextante toolkit) is friendlier to use than the qgsAffine plug-in. N. – nhopton Sep 11 '12 at 12:03
By the look of it v.transform will do the sums for you as well, see grass.osgeo.org/gdp/html_grass63/v.transform.html – nhopton Sep 11 '12 at 12:28
up vote 1 down vote

Following-on from my comments on Rayner's answer, GRASS v.transform, which can be run from the Sextante toolbox, can be used to calculate transformation parameters and apply them to a vector layer to perform an affine transformation. A text file containing control points is required, in the format shown here.

It's very easy to use and works well.

N.

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up vote 2 down vote

see my answer in this thread: Snapping two polygons together and give the free openjump a try. its affine transformation is much more userfriendly than qgis affine plugin

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up vote 3 down vote

Given the fact that you have some points of control, you should be able to use an Affine transformation to shift your vector data. Have a look at this recipe. The process is a two part process:

  1. Use your control points to define the coefficients of your affine function required
  2. take the coefficients and apply them to the ST_Affine() in postgis.

If you put your control points into a CSV file (old_x,old_y,new_x,new_y), you can just about cut'n paste the R commands from the link to solve the coefficients part.

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