[Qgis-user] Re: georeference plugin, maximum distortion needed, and black background

[Roland Hill]

You can make the black surrounds to your warped image transparent by 
right clicking on the layer, choosing properties, then selecting 
Transparency. Add a new entry to the Transparent Pixel List using the 
button with the star, then put 0 in for Red, Green and Blue (or 255 for 
white backgrounds).

Roland




mtnbiketrail at zzz.com wrote:
> I'm trying to geo-reference some rasters.
> I'm not sure which algorithm to use to get maximum match with known 
> GCPs, these rasters need to be distorted a lot. I thought tps and 
> cubic would be best. Can anyone tell me which algorithm is best?
>
> Also, when the raster is placed(georeference completed), the 
> background outside the original raster is black, not transparent like 
> I would expect. I doubt I can trim the modified raster without losing 
> GCPs. I can make the raster transparent, but I don't like the 
> results.  Is there a solution to the black background?
>
> Once I am satisfied with geo-referenced rasters, I can trace vector 
> polylines inside QGIS. Or is there a better way? Using a vector 
> drawing program like Inkscape or Adobe Illustrator?
>
> I'm potentially dealing with a lot of data, so am looking for the best 
> way.
>
> thanks,
> Tom
> using 1.3
>
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