Engineering Rock Mechanics

Hemispherical projection methods 433

Small circle

Inclined plane projection

\ 1 ./

......... ........ .~ 0 Q

....

.'.. ...

9..

results on

Trace of P on surface of 'u .......

hemisphere, as inclination of

plane varies

Rather than draw great and small circles for every application, we use
pre-printed grids showing these circles at angular separations of, say, 2".
These grids enable us to plot and measure lines and planes of all
orientations. They are called equal angle equatorial projections (because
they look like a globe viewed from a point above the equator), but
commonly are known as hemispherical projection nets.