Thanks for the input Nicolas These are official maps so the utm grid is ok. I figured that I was using a linear transformation, with the option to just create the world file, which works for control points at the corners (lat/long), since the boundaries of the map is defined by latitude/longitude. With UTM, this simple transformation won't work, but TPS will give the correct results.
Carlos On Thu, May 17, 2018 at 7:28 PM, Nicolas Cadieux < [email protected]> wrote: > Hi, > The utm grid is way off or we have the wrong epsg code. If you geofence > using 2 points (linear algo) using a service like google earth, you will > see the distortion. The long lat coordinate are probably ok but I did not > test them. > > You can either use the long lat or use more points. With 4 points and > using the thin plate spline, I got good results. > Nicolas > > Le 17 mai 2018 à 12:42, Carlos Henrique Grohmann de Carvalho < > [email protected]> a écrit : > > Thanks Nicolas, but the misalignment still persists. OTF is off, project > has same CRS as data (epsg 29192). There is a ~400m difference in the N-S > direction. > > Carlos > > On Thu, May 17, 2018 at 1:28 PM, Nicolas Cadieux < > [email protected]> wrote: > >> Hi, >> Disable projection on the fly. Make sure the project is in the same CRS >> as your maps. >> Nicolas >> >> Le 17 mai 2018 à 12:14, Carlos Henrique Grohmann de Carvalho < >> [email protected]> a écrit : >> >> Hello all >> >> I have two pngs of topographic maps from southeastern Brazil (a zip file >> with images and points is available here: https://www.dropbox.com/ >> s/mexeh4be46pgsk6/images_georef.zip?dl=0) >> >> I'm trying to georeference them, but with partial success only. In this >> image (https://www.dropbox.com/s/37xxqp4fkwpdyqh/utm_error.png?dl=0) you >> can see that the X coordinate is fine, but the Y coordinate of the two maps >> won't match. >> >> Both maps use South American Datum 1969. I selected points near the >> edges, and used the UTM values. >> >> Interestingly, if I use Lat/Long, and place the points at the corners, >> using decimal degrees, the maps align perfectly. >> >> >> Any help is appreciated >> >> >> -- >> Prof. Carlos Henrique Grohmann >> Institute of Energy and Environment - Univ. of São Paulo, Brazil >> - Digital Terrain Analysis | GIS | Remote Sensing - >> >> http://carlosgrohmann.com >> http://orcid.org/0000-0001-5073-5572 >> ________________ >> Can’t stop the signal. >> >> _______________________________________________ >> Qgis-user mailing list >> [email protected] >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user >> >> > > > -- > Prof. Carlos Henrique Grohmann > Institute of Energy and Environment - Univ. of São Paulo, Brazil > - Digital Terrain Analysis | GIS | Remote Sensing - > > http://carlosgrohmann.com > http://orcid.org/0000-0001-5073-5572 > ________________ > Can’t stop the signal. > > -- Prof. Carlos Henrique Grohmann Institute of Energy and Environment - Univ. of São Paulo, Brazil - Digital Terrain Analysis | GIS | Remote Sensing - http://carlosgrohmann.com http://orcid.org/0000-0001-5073-5572 ________________ Can’t stop the signal.
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