I have created a points layer which represent Ground Control Points (GCP) for georeferencing scanned topographic maps via 'Add Layer > Add Delimited Text Layer', where I saved coordinates in a .csv format that has the lat-lon of each point, stored in DMS coordinate system (I am using DMS as the scanned topo maps use DMS).

I have managed to load the .csv as a Shapefile. Now, I open up the Georeferencer, load the scanned topo map, and click 'File > Load GCP points', however it requires a Ground Control Point file with the *.points extension, and not a Shapefile.

I would prefer not to manually reassign all the control points. How do I convert a Shapefile to a GCP (.points) file? If that is not possible, how do I create a GCP (.points) file? What file formats can I use to create the required GCP (.points) file?

My goal is to be able to load it into the Georeferencer. I am using QGIS 3.2.1.

When I change the extension of the .shp to .points, it becomes a POINTS file (.points), but QGIS will prompt me the following; "Invalid GCP file. File could not be read."

  • Does your shapefile already contain the information about which pixel, expressed as rows and columns, is under each GCP? – user30184 Nov 12 '18 at 7:52
  • No, it does not have the which pixel row and column a point belongs to. It only has the lat-lon in DMS coordinates. – Johanness Nov 12 '18 at 8:01
  • If you do not have extremely many GCP's I think it is easiest and fastest to insert them again with the QGIS georeferencer. – user30184 Nov 14 '18 at 7:22

how do I create a GCP (.points) file?

You could use a text editor.

The format you want is like:

  • Okay nmtoken, but how do I get those values for pixelX, pixelY by using my GCPs and a non-georeferenced raster (scanned) map? I only have the lat-lon coordinates of my GCPs in DMS coordinate system. – Johanness Nov 12 '18 at 9:08

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