To measure angles, we need to rotate the net relative to the tracing paper. It is used to measure angles on the projection. The stereographic net or stereonet is the 3-D equivalent of a protractor. The projection itself, or stereogram, is usually drawn on tracing paper, and represents a bowl-shaped surface embedded in the Earth. There are two parts to any stereographic projection. Wullf net for plotting and measuring features on a stereographic projection The on-line visualization tool at may also help. Try to imagine that you are looking down into a bowl-shaped depression in the Earth’s surface. However, if you have already met the stereographic projection in mineralogy, the lower hemisphere may take a little getting used to. There is a good reason for this: the lower hemisphere represents the region beneath the Earth’s surface where the rocks have not yet been eroded away. Whereas crystallographers use an upper hemisphere projection, structural geologists always use the lower hemisphere. However, there is one important difference. and is a popular method used by crystallographers as a tool for representing crystal form. Stereographic projection has been in use since the second century B.C. However, it is extremely useful, as orientation problems are very common in structural geology. Unlike structure contouring and other map-based techniques, it preserves only the orientation of lines and planes with no ability to preserve position relationships. Stereographic projection is a powerful method for solving geometric problems in structural geology.
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