$Id: reflect_map.pro 7092 2010-01-12 20:18:45Z jimm $ NAME: REFLECT_MAP PURPOSE: Reflect the viewer through the plane of a map projection to the opposite side. This results in reversing the x axis. This procedure CATEGORY: Mapping CALLING SEQUENCE: REFLECT_MAP Should be called immediately after calling MAP_SET. SIDE EFFECTS: Changes !x.s. PROCEDURE: Map projections of the sphere usually are understood to have the viewer of the plane of projection outside the sphere. Sometimes the viewer may be understood to be inside the sphere, i.e., on the other side of the plane of projection. When the veiwer is on the other side of the plane, this requires reflecting the plane about the y-axis so that +x is to the right rather than to the left. This procedure should be called only once immediately after setting up the map projection using MAP_SET. EXAMPLE: The Astrid PIPPI instrument has a natural right-handed spherical coordinate system. Measurements are naturally thought of as occuring on the surface of the sphere where each angular position corresponds to a different measurement look direction. IDL's map projection procedures can be very useful for displaying the instrument measurements. However in this case, the viewer of the map projection plane is on the opposite of the viewing plane because the viewing is from inside the sphere (i.e. from the point of view of the instrument). Another way of thinking of it is that the viewer is reflected through the sphere (r -> 1/r). For proper display with IDL's mapping procedures this requires that the viewing plane x axis be reversed so that +x remains to the right hand of the viewer. MODIFICATION HISTORY: Sat May 27 16:12:29 1995, Chris Chase Created.