Wrapped Sets

Wrapped Sets refers to sets which contain poles on opposite sides which "wrap" around the perimeter of the stereonet. It is important that set windows are correctly defined for poles that wrap around the stereonet:

• Curved Set Windows: Wrapping is handled automatically when the second corner is extended beyond the stereonet perimeter and wraps around to the other side.
• Circular Set Windows: Wrapping is handled automatically when the cone wraps around to the other side.
• Freehand Set Windows: Wrapping must be handled manually by drawing the Primary Window AND Secondary Window and selecting the Wrapped checkbox to indicate that one of the windows is wrapped.

Mean Vector Calculation for Wrapped Set Windows

The mean vector calculation for Sets created with a regular (i.e., non-wrapping) Set Window is simply the vector addition of all the poles within a window, which is then normalized to the sphere boundaries.

WARNING: When pole vectors are clustered near the equator, and plot on opposite sides of the stereonet, a mean orientation calculated from the Lower Hemisphere alone will be incorrect!

The Wrapping Set window capability of Dips automatically accounts for this situation. The poles within a Wrapped Set Window that plot on the opposite side of the stereonet are incorporated into the vector addition as negative poles (i.e., plunge = -plunge, trend = trend + 180), so that the mean will be correctly calculated.