Usage: gdal_viewshed [--help] [--help-general]
[-b <band>]
[-a_nodata <value>] [-f <formatname>]
[-oz <observer_height>] [-tz <target_height>] [-md <max_distance>]
-ox <observer_x> -oy <observer_y>
[-vv <visibility>] [-iv <invisibility>]
[-ov <out_of_range>] [-cc <curvature_coef>]
[-co <NAME>=<VALUE>]...
[-q] [-om <output mode>]
<src_filename> <dst_filename>