geometry_quadrilateral index x_0 y_0 z_0 x_1 y_1 z_1 x_2 y_2 z_2
x_3 y_3 z_3 tolerance

This data item defines a quadrilateral in space. Other data items can check if nodes are located on this geometry. The coordinates of the corner points are x_0 y_0 z_0 etc.. In 2D, only x_0, y_0 etc. should be specified etc.. The points of the quadrilateral should be specified in the correct order; the order is clearified in the example below.

All node within a distance tolerance are considered to be part of the quadrilateral (this gives a brick with thickness $2 \ast tolerance$). Internally in TOCHNOG, the quadrilateral is divided into two geometry_triangles, which is only approximately true if the quadrilateral is twisted. Example

...
number_of_space_dimensions 2
...
geometry_quadrilateral 0 0. 0. 1. 0. 0. 1. 1. 1.
...

Notice the order in which the points are to be specified.