The goal is to make converting scanned paper maps to map tiles as easy as possible.
I've done a few, but the slow part is manually entering coordinates of points. What I'd like to do is for each point on the scanned paper map, click on a satellite image (ie a Google Map) to automatically set its coordinates. I know this should be possible with QGIS and the georeferencer plugin (I'm using 1.7.2) but…
If I set QGIS to use WGS84 projection, I haven't found a way to display Google Maps in QGIS so that the georeferencer plugin tool will take coordinates from it.
If I set QGIS to use EPSG:900913, I can use the Openlayers plugin to add a Google Maps layer, and the georeferencer plugin tool happily takes coordinates from it. But gdal2tiles won't process the resulting geotiff file that georeferencer produces.
So currently I set QGIS and georeferencer to use WGS84, type in lat/lon pairs manually, and then gdal2tiles processes the resulting geotiff successfully.
Has anyone found a workflow that avoids the problems I described above?
Thanks & regards, David
Best Answer
As already said, you cannot reproject layers from the "openlayers" plugin, but you can indeed use them as overlay to georeference another raster image. When finalizing the operations the georeferencer will ask you for a number of parameters, among the other "Target SRS", this means that you can use a map in a certain coordinate system (ex: 900913) to georeference another one, and have the output automatically warped in another one (ex: WGS84).
You can do also the other way: create your GCPs in WGS84, translate them in 900013 and then use them to georeference the map.