This data item defines a circle segment in space.
Other data items can check if nodes are located on this geometry.
The coordinate of the center is *x_c y_c*.
If *side_x* is set to a positive value, say +1.,
then only x-values larger then *x_c* are considered
to be part of the geometry.
If *side_x* is set to a negative value, say -1.,
then only x-values smaller then *x_c* are considered
to be part of the geometry.
If *side_x* is set to 0 ,
then all x-values are considered
to be part of the geometry.
Likewise remarks hold for y-values.
All **node** within a distance *tolerance* of the radius are considered to be
part of the circle segment.

tochnog 2001-09-02