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

You could use a text editor.

The format you want is like:

mapX,mapY,pixelX,pixelY,enable
433268.37959376286016777,355509.77655098377726972,983.9774984446378312,-2014.51289408103730239,1
433246.04284725664183497,355552.3686015487764962,831.61904507316751278,-1719.29808785451632502,1
433306.56253424676833674,355622.24824787728721276,1234.15815910973515201,-1236.85959025535225919,1
433411.46138055482879281,355677.74274208577116951,1955.41727764171605486,-850.47783687136427488,1
433554.34018561965785921,355695.8543699209112674,2953.81013592618046459,-710.01017688100557734,1
433636.94680135982343927,355569.64276779681676999,3522.92258485503180054,-1576.07810653126352918,1
433600.53707709873560816,355540.0109893383923918,3268.11243895852203423,-1781.04650243362743822,1
433454.43287125352071598,355434.66971611470216885,2264.11336592998168271,-2498.8375497027768688,1
433346.00189347146078944,355440.21874731522984803,1527.95157730500841353,-2474.08382017634630756,1
  • 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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