When defining the geometry of the wedge and slip surfaces using space projection, the program displays individual surfaces with the help of great circles (in equal are net) of Lambert's hemispherical projection.
Principle of Stereographic projection (Lambert's projection)
Markland test utilizes a stereographic projection of the great circle for the kinematic possibility of the rock wedge failure. The geometry of the rock wedge is plotted on the stereographic projection using the great circle representing the slope face and discontinuities of slip surfaces 1 and 2 (see figure). The friction circle is plotted on the projection too, the friction angle on the discontinuities is measured from the north and the circle center is the center of the stereograph. The zone between the great circle representing the slope face and the friction circle is a shaded area on the figure. When the plunge of the line of intersection of two discontinuities (1 and 2) is in the shaded area, then the failure is cinematically possible.
Kinematic possibility of the rock wedge (Markland's test plot in a stereographic projection)
View of the geometry of the rock wedge is supplement by elements of Markland's test plot. This makes it possible to assess the stereographic projection of the kinematics of the rock wedge.
Markland's test plot