GRASS's v.transform: https://grass.osgeo.org/grass70/manuals/v.transform.html might also be useful here.
Paul On Thu, Apr 6, 2017 at 11:10 AM, Andre Joost <[email protected]> wrote: > Am 05.04.2017 um 20:46 schrieb Brock Riedell: > >> I have some downloaded geologic map shapefiles that were digitized >> incorrectly in UTM space, and they render a few hundred meters away from >> their proper locations on georeferenced U.S. topo maps as well as on >> Google, Bing, and ESRI online base map data. This is too much for datum >> shift; the NAD27 to NAD83 transformation should offset coordinates about >> 90 m. I have determined that the correction involves a counterclockwise >> rotation of ~1.4 degrees and not a simple translation. I have reviewed >> the PROJ.4 documentation about using the 7-parameter 'towgs84' options >> to add the rotation. I have not been able to get this working by trial >> and error; the data plot out 150-200 km away from where they should be. >> Questions: >> >> (1) Do I need to input the rotation value as both Rx and Ry? >> (2)The documentation says rotations are input as seconds of arc rather >> than degrees, correct? >> (3) How does the scaling parameter in towgs84 interact with the scale >> factor k_0? >> > > The towgs84 parameters are really ment for small rotations only. If you > have big rotations, think of using a custom oblique mercator transformation. > > You can find an example at http://gis.stackexchange.com/q > uestions/83861/using-customized-coordinate-system-in-arcgis-desktop > > HTH, > André Joost > > > _______________________________________________ > 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
_______________________________________________ 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
