Cuts the triangles in a triangle list with a plane perpendicular to an axis (for use with selected TDPACK routines).
Available in version 4.3.1 and later.
procedure tdctri ( rtri [*] : float, ntri  : integer, axis  : integer, rcut  : float )
A float input/output array, dimensioned mtri x 10, in which a list of triangles has been stored, probably by means of calls to tdstri and/or tditri. The number of triangles in the list may increase as a result of calling tdctri.ntri
An input/output integer specifying the number of triangles currently in the triangle list. Its value is increased by each call to a triangle-generating routine like tdstri or tditri and may be increased by calls to tdctri or tdotri. This value should have been set by a previous routine like tdctri.axis
An integer scalar specifying which axis the "cut plane" is to be perpendicular to. The value 1 implies the U axis, the value 2 the V axis, and the value 3 the W axis.rcut
A scalar float specifying where along the axis specified by axis the "cut plane" is to pass through that axis.
This routine is part of the low-level TDPACK package, which is a group of Fortran and C callable routines for projecting objects from a 3-dimensional coordinate system having U, V, and W axes to a 2-dimensional projection plane having X and Y axes and/or for drawing the projections of those objects. This can be referred to somewhat loosely as "drawing objects in three dimensions".
This routine, given a list of ntri triangles in the array rtri and a couple of arguments specifying a plane perpendicular to one of the axes, finds all the triangles in the list that intersect that plane. Each such triangle is broken into smaller triangles which lie entirely on one side of the plane and those triangles replace it in the list.
The object of calling tdctri is to slice a surface up in such a way that its rendering can be made in some way dependent on the position of the surface.
Please see the documentation on TDCTRI for a full description of this procedure.