On Wednesday 28 November 2007 8:00 pm, you wrote: > You need to set the default projection (projector icon at lower right) > to be the same as your aerial photo and check "Enable on the fly > projection" (top of default projection dialog). Then open your vector > road layer.
Hi Tom, Unfortunately, setting the default projection to that of the aerial photo has been difficult because the photo is in 3TM projection (Alberta's very own projection that, I think is based on, or is similar to, Canada's 3 degree UTM projection...I'm still trying to wrap my head around this). I built the aerial photo from a mosaic of slides from here: http://gis.lethbridge.ca/website/LethWebMAP/viewer.htm If you click on the map with the xy tool, you'll see 3TM Northing and Easting data. Since I do not know how to georeference the photo using 3TM coordinates because as far as I can see neither QGIS or GRASS has a 3TM projection option, I thought I would georeference the photo to UTM instead. Here's what I did: I opened a "roads" shape file of the same area and wrote down the UTM coordinates of eight locations. Then I used the georeferencer plugin to reference these eight locations on the photo. Then when I open the raster layer of the photo and add the vector layer on top, the photo is off (it needs to rotate clockwise just a bit) . If I check the coordinates on the raster layer, they are not the same as what I entered during the georeferencing step. For example an intersection in the upper right of the photo was referenced as: x=368635.635, y=5513144.723 but when I open the photo as a raster layer and check that location I see it's: x=368583.800, y=5513186.800 Perhaps I did something wrong when I georeferenced the photo? Thanks. -- Peter Pankonin, digitalcrucible There are 10 kinds of people in the world, those who understand binary, and those who don't. _______________________________________________ Qgis-user mailing list Qgis-user@lists.qgis.org http://lists.qgis.org/cgi-bin/mailman/listinfo/qgis-user
