Shapefile’s Georeference

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Lately, I found some cadastral data in dwg format in order to extract parcels for a research of mine. Through use of  Draftsight  I converted this kind of file in dxf format, much more readable in a Gis Open Source like QGIS. But, when I was opening those files I discovered that Draftsight doesn’t have assigned any reference system to my data, leaving it in x-y undefined coordinates.

 

Because of convenience reasons, I performed a one more conversion, now in shapefile format. Then,I compared the own vectorial in dxf with one having known coordinates in WGS84 in order to extrapolate GCP – Ground Point Control by Catch Coordinates of QGIS.

Gathering the set of common points, I assigned the georeferencing operation by ogr2ogr by command line in a linux shell. Here, we can see the command sintax for perfoming this kind of operation:

ogr2ogr -t_srs  [srs_def]  -gcp  x_nongeoref   y_nongeoref   x_georef   y_georef  out.shp in.shp

where:

  • -t_srs [srs_def] is an option for the output reference system
  • -gcp  declares gcp points
  • in.shp input  file ( x-y coordinates)
  • out.shp output file (georeferenced file)

 

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