Synopsis
		sfcgconst < in.rsf > out.rsf mask=mask.rsf source=o2 w=0. v0=1. b=0. p=1/v0

Parameters
		float b=0. velocity gradient   file mask= auxiliary output file name   float p=1/v0   float source=o2 real source point   float v0=1. surface velocity   float w=0. beam width