Using QGIS to Georeference images

It is pretty easy and straightforward to use QGIS to georeference raster images.  There is a georeference plugin that is installed by default.

To use it:

  • Go to the Plugins menu, Manage Plugins, and turn on the Georeferencer GDAL plugin.
  • Load your layer containing the control points the raster is to be tied to
  • In the Plugins menu go to the Georeferencer entry and select Georeferencer
  • In the Georeferencer window load the raster to be georeferenced
  • Click the “Add Point” button, then select your first control point on the raster
  • In the window that pops up click the “From Map Canvas” button
  • In QGIS use the “Toggle Editing” button, it looks like a pencil, to select the corresponding control point
  • Go back to the Georeferencer window to select the next control point.  You’ll need at least 3 points
  • Once you have all your points click the “Start Georeferencing” button in the Georeferencer window
  • From the new window that pops up you can set your coordinate system, decide if you want a seperate world file, and if you want a pdf showing a report of the actions performed among other things

 

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    • chandu
    • May 22nd, 2014

    if i am georeferencing a scanned map, which has a projection X, then the scanned version has no projection (units are in mm or inches). So what should I set the input raster projection as, or does it not matter? And then I am constrained to set the target SRS as the projection of the original map, right? The lat-long values I enter for the corner points of the topo correspond only to that projection.

    • Set the projection to the projection or CRS of the data you’re georeferencing the image against. That way the coordinates you give the point you select on the image match the coordinates you provide from your source data. Once the image is referenced you can re-project it to any projection you want or need.

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