Earlier I was trying to figure out why Composer wanted to export raster
files, and I wanted vector. I finally reduced my 'map' to the raster
base map and one local shape file, Roads. With this I found that
selecting the layer Roads and using "Set Project CRS to this Layer" was
causing Composer to default to raster output. A clue!
I had noticed that the raster base map rotated 2 or 3 degrees CW when I
used "Set Project CRS to this Layer", above. I also noticed that in
Composer, if I had not used "Set Project CRS to this Layer", placing a
UTM grid on my map resulted in the grid being rotated 2 or 3 degrees
CCW. So, it appears that the grid is based on the base map?
In reading today's posts, I noted mention of Georeferencer. Digging
into this, the tutorials, etc seemed to require having another input, to
compare points. I thought I might be able to accomplish this by
comparing my Roads layer with the raster map.
I loaded my local Roads shape file into a new canvass in QGIS and my
raster base map into Georeferencer. I would click a particular
intersection in georeferencer and it would produce the 'enter
coordinates' or 'get from map' options. Selecting the latter, it
switched to the map canvass and I could zoom in and click the same
intersection. This would send me back to the previous menu where the
coordinates were filled in and I would select OK. I did this on 4
points. On the fourth point, I noted the red line angled 2 or 3 degrees
CW, but quite long.
I saved the points in a file and Started Georeferencing. The completed
raster base map came up on the QGIS canvass, along with the Roads shape
file.
What I saw did not please me. In some places, the Roads were now
falling at least 1/2 kilometer off from the base map road locations.
This put them in creek ravines and other hillshade elements. The
results were unusable for my purposes.
When I had used "Set Project CRS to this Layer", the Roads layer fell
onto the roads on the raster map. Streams fell onto their ravines.
Maybe I have to get another base map? Or maybe my georeferencing method
was faulty?
Stephen
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