Hi Bruce and others, I think the functionality to compute the affine transformation coefficients from a set of control points would be a useful and welcome addition to the Postgis tool-set.
I agree with you that it would be very nice to have an interactive tool to edit individual control points in the link table in a Desktop GIS, such as QGIS or uDig. QGIS already has a tool for georeferencing rasters, so maybe some of the GUI and functionality could be re-used for the adjustment of vectors as well. I don't know too much about uDig. I am more a QGIS user. I would be willing to test both, a non-interactive Postgis-function and an interactive tool in Desktop GIS. Andreas > Based on a previous post on affine transformations of GIS data in PostGIS, > I > have put together a function that takes a table of control points and > computes the affine transformation coefficients using the least squares > code > from GRASS. A nice tutorial by Dylan Beaudette on this is at: > http://casoilresource.lawr.ucdavis.edu/drupal/node/433 > > At this point I would like some feed back on how this could be used. I > envision a GIS package (say uDIG) would allow a user to select pairs of > points and populate a table with a similar layout as ESRI's link table > when > georeferencing. A query would give the RMS error and similar query would > return the table back with the residual errors. If the user were then > happy > with the values (after deleting poor matching points), a final query could > then be made to the ST_Affine function to modify the geometry based on the > control points. > > Comments? > > Bruce Rindahl > > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > -- Andreas Neumann Böschacherstrasse 6, CH-8624 Grüt/Gossau, Switzerland Email: [EMAIL PROTECTED], Web: * http://www.carto.net/ (Carto and SVG resources) * http://www.carto.net/neumann/ (personal page) * http://www.svgopen.org/ (SVG Open Conference) * http://www.geofoto.ch/ (Georeferenced Photos of Switzerland) _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
