There is a saga gis visibility module. You could run that through processing if you have qgis 2.0.1
– johanvdwNov 13 '13 at 08:20
If we're guessing about the question as duplicate, then it isn't clear enough. Please put some effort into describing the problem (not just naming it)
– BradHardsNov 13 '13 at 10:50