> Le 18 mai 2018 à 00:28, <[email protected]> <[email protected]> a écrit : > > I haven't been able to open the dataset but going through the discussion I > would like to offer some assistance since I believe there are some > misconceptions here: > > First, the data has nothing to do with the NAD27 / NAD83 datum's since these > are North American datum's and they don't apply I believe in South America. > Moreover, the separation between NAD27 to NAD83 is about 100m. I think Carlos > mention something like being 400m off. > > Another point of confusion is about the projection of Google Earth. Google is > using a Web Mercator projection based on a perfect sphere. This has nothing > to do with the UTM that has already incorporate the Earth Flattening values > into the Northing and Easting equations. > > If I find some time tomorrow, I will come back and give the proper equations > showing the difference between Google's projection and UTM. > > -0x906 > > > >> On 2018-05-17 19:53, Carlos Henrique Grohmann de Carvalho wrote: >> >> 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. >> >> _______________________________________________ >> 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 >
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