On Wed, 5 Apr 2017 11:46:57 -0700, Brock Riedell <[email protected]> wrote:
> 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 It seems that it fits completely the definition of an affine transformation. There is a plugin with this name that should do the magic. HTH > 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? > > > Thanks and regards > Brock > > Roxo -- ---------------- Non luctari, ludare -------------------+ WYSIWYG Fernando M. Roxo da Motta <[email protected]> | Editor? Except where explicitly stated I speak on my own behalf.| VI !! ( Usuário Linux registrado #39505 ) | I see text, ------------ Quis custodiet ipsos custodes?-------------+ I get text! _______________________________________________ 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
