I have merged about 20 OS tiles in to a single raster and I am trying to clip the merged tiles using a single polygon which itself was created from a small number of ward boundaries, merged using the edit - merge selected features. The polygon boundaries fall entirely within the raster.
When I try to use the raster - extraction - clipper command I get the error message "cannot compute bounding box of cutline"
I have seen previous questions on the subject and the answers point to using different projections but I am using the same CRS. Another solution was to reproject to raster but that has now been running for several hours and has still not completed.
I'm thinking that I'm missing something obvious here but can not for the life of me work out what it is. The only thing that came to mind is that the OS tiles come with their own georeference files. By merging them have I lost that. The merged raster appears in the correct position though.
How can I clip the raster to match the wards?