[Qgis-user] Georeffrenced Tiffs in QGIS 1.8.0

[Andre Joost]

Am 04.03.2013 10:16, schrieb Richard Ford:
> I have been trying to project some raster charts in a GeoTiff format
> for a while now with no luck. They always seem to be completely out.
> Not just on the wrong side of the plant but completely off the
> planet. All vector data I am using is projecting correctly using the
> same WGS84 UTM projection. I have tried the raster ->  projection ->
> assign projection with no success.
>

You have to understand the basic difference between reprojecting and 
assigning a projection:

If your raster units are degrees or parts of that (like DEM), you have 
to assign the Geotiff CRS to a geodetic CRS, like WGS84 (lat/lon).

If your raster units are in metres, you have to look for an appropriate 
projected CRS.

If you are not sure about it, you can rightclick on the layer -> 
Properties, Metadata tab, and look for "Extent". If it is in a range of 
+/- 180/90, the data is in a geodetic CRS (lat/lon).

Unless you have a georeferenced image (with jpw, tifw or world file), 
you have to use the georeferencer plugin to connect the raster cells to 
geographic coordinates. If you do that by clicking ideintical points on 
the map canvas, the output CRS must be the same as the project CRS.

If you need to change the CRS of a Geotiff file, you have to use Raster 
-> projection -> reproject.



HTH,
André Joost