Engineering Rock Mechanics

434 Appendix 0: Hemispherical projection

Using a hemispherical projection net: plotting vectors

Never write on the net: always use a piece of tracing paper over it.
Carefully pierce the centre of the projection with a drawing pin, and then
push the pin through from the reverse side of the net. Use the point of the
pin to hold a sheet of tracing paper in place. Mark the north point as a
datum.

N

Mark, with a tick on the perimeter

of the net at the correct azimuth, the

vector to be plotted. Write on the

projection the orientation. Only

write on the tracing paper, not the

net.

Rotate the tracing paper so that

the tick is on the E-W lie. Count

in an amount equal to the dip of

the vector. Mark the position of 219168

the vector. Only write on the

tracing paper, not the net.

N

Rotate the tracing paper back to the

datum: the position of the vector is

now correct relative to north.