|This routine sets the rotation angle for the y axis labels on
a linear, log or 3-D axis.
In order to provide a common interface to axes label angles some definitions
need to be made. We have defined positive x to be from left to right
and positive y and z (in a 3-D plot) to be from bottom to
top. The angle is in reference to the positive axis and increases in a
counter-clockwise direction. Above corresponds to positive angles, and
below corresponds to negative angles.
For example, in a normal x-y plot with the x axis
on the bottom and the y axis on the left, the labels are
below the x axis and above the y axis. On a 3-D plot
positive x and y go away from the corner at which the axes
meet so that both x and y labels are below the axes. It might
be helpful to think of the angles as being defined on an x axis
and then rotated to the appropriate axis.