def internalViewshedAlgorithm(self,n,analysis_type,dem,precision,miss_params,item):

        # if feedback.isCanceled():  break



        matrix_vis = ws.viewshed_raster (analysis_type, value, dem,

                                        interpolate = precision > 0)




        # must set the mask before writing the result!

        mask = [item[1]["radius"]]




        inner_radius_specified = "radius_in" not in miss_params

        if inner_radius_specified:

            mask += [ item[1]["radius_in"] ]




        if  "azim_1" not in miss_params and  "azim_2" not in miss_params:

            if not inner_radius_specified:

                mask += [ None ]

            mask += [ item[1]["azim_1"], item[1]["azim_2"] ]

            print (mask)




        dem.set_mask(*mask)




        r = dem.add_to_buffer (matrix_vis, n, report = True)





        report.append([item[1]["id"],*r])