  Standard photographs of streamer discharges show a two-dimensional
projection. We here present stereo-photographic images that resolve their
three-dimensional structure. We describe the stereoscopic set-up and
evaluation, and we present results for positive streamer discharges in air at
0.2 - 1 bar in a point plane geometry with a gap distance of 14 cm and a
voltage pulse of 47 kV. In this case an approximately Gaussian distribution of
branching angles of 43 degrees is found; these angles do not significantly
depend on the distance from the needle or on the gas pressure.
