## Average IDF and RIDF plots.

**A** We produced volcano plots comparing normalized scene differences (IDF) of each scene to all 1800 scenes in the room. Slices were taken through each plot along the north-south and east-west axes. Each slice was then divided at its focal point, with the falling phase of each slice inverted and aligned with the rising phase. This produced four rising curves for each of the 1800 volcanoes, or 7200 separate vectors for the entire room. The family of curves shows average values of these 7200 vectors with distance from the focal scene for each of the eight sensor resolutions (all at 10 levels of gray). **B** Plot of p50 values in meters (= points x 12.7 m) from the focal scene for the eight sampled resolutions. Dotted line is a 6^{th}-order polynomial fitted to the points (R^{2} = 0.99996). **C** RIDF plots were produced for all 1800 scenes at 360 degrees for the eight sampled sensor resolutions (all at 10 levels of gray). Only the first 40 degrees are shown because the curves remain flat to 180 degrees. The plots were produced as described in A, except that the total number of vectors was 3600. **D** Plot of p50 values in degrees for the eight sampled resolutions. Dotted line is a 6^{th}-order polynomial fitted to the points (R^{2} = 0.99932).