> Date: Tue, 12 Jul 2011 08:53:14 +0200 > From: [email protected] > Subject: Re: [Qgis-user] use raster + GCP points + ?? as data > To: <[email protected]> > Message-ID: <[email protected]> > Content-Type: text/plain; charset=UTF-8; format=flowed > > On Mon, 11 Jul 2011 23:27:14 -0700, Alex Mandel wrote: > > On 07/11/2011 10:30 PM, Richard Duivenvoorde wrote: > >> Hi all, > >> > >> I have these pile of scanned old maps and can georeference them with > >> the > >> good working georeferencer plugin in qgis. > >> > >> But do NOT want to really warp the image. Why should we want to > >> store > >> TWO huge rasters, maybe loosing 'data' contained in the 'original'? > >> > >> So my question: is it possible (for Qgis, but preferebly also with > >> other > >> tools (wms's) to load data from the original raster, probably > >> accompanied with a txt file with GCP points (or maybe some other > >> format > >> containing both gcp points and projection/transformation > >> information)? > >> > >> Is there some 'common' way for the the world of gis? > >> > >> Thanks for any thoughts, > >> > >> Richard Duivenvoorde > > > > > > A world file is the common way. It describes the coordinates of the > > corners, how many units per pixel and what skew if any. See the > > wikipedia page for details. > > > > I believe the georef plugin can save the a world file for you. > > > > Thanks, > > Alex > > It doesn't enable for all the transformation methods.
In many situations this wouldn't be a problem. Another issue though is that IIRC the georeferencing plugin can't create world files with rotation. > Richard > this choice has a huge trade-off with most formats, the time > to resample the raster each time the users move the canvas will not be > accepted by them. Storage is cheaper and does not interfere with your > users. If the size is a huge issue and not the quality of > representation, you can reduce the original resolution. Personally I haven't been able to detect _any_ slow-down with on-the-fly raster reprojection, which did surprise me. But obviously this can't be a problem if the project coordinate system is the same as the scanned map. Alister _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
