Upward openness maps show ridge crests in white, while downward openness maps show valleys in white. They provide dramatic depictions of terrain.
Upward (Positive) openness
Downward (Negative) openness
Choice of upward (positive) and downward (negative) openness. For each select a region size in meters, because openness is defined as a maximum or minimum angle over a specified region. The region size should be at least as large as the ridge/valley spacing in the region. The Graph parameter by Region size option can help you pick the value by seeing the inflection points.
|Openness calculates an angle in each of 8 radials in the
principal compass directions. The diagrams to the left shows two of the
angles computed for upward openness. The peak in the top diagram will have
a high value for openness, while the valley in the bottom diagram will
have a small value.
The Value L shows the distance used for the computation; for the peak, visibility extends all the way out to L, while for for valley, the steep walls block visibility well before the L distance.
Openness maps correlate strongly with maximum and minimum curvature.
Short distance openness maps can be very effective with urban lidar DSM.
References for openness maps
Last revision 11/26/2017