ISOTR                                                              Menu: PRISM
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Creates a right-angled triangular (isosceles) polygon or a solid right-angled
triangular prism based on the polygon.

        1. * (CHAR) plane of triangle (x-xy,y-yz,z-zx) <x>
        2. * (POINT) starting point
        3. * (NUM) edge length
     for option `x':
        4. * (NUM) height of prism
     for options `y' or `z':
        4. * (NUM) length of prism
     for all options:
        5. * (Y/N) positive prism? <y>

Description:
This command creates a right-angled triangular (isosceles) polygon or
a triangular prism based on the polygon.
The triangle will be right-angled at the starting point; the two other angles
will both be 45. Specify one of the axial planes; (x xy plane, the default; y
yz plane, z  xz plane). Define a starting point. Specify the edge length
(greater than 0) and the prism height (for `x' option) or the length (for `y'
and `z' options). You may enter `0' for a 2D polygon. Enter `y' (the default)
for a positive prism or `n' for a negative one. The edge length specified
refers to the two shorter sides of the triangle (not the hypotenuse). The
orientation of the triangle is such that the two equal sides extend from the
starting point in a positive direction parallel to the two axes defining the
plane of the triangle. You are prompted to create more prisms until another
command is selected.
        Example: \isotr x 0 0 0 4 3 y
        Result: A positive solid triangular (isosceles) prism is created with
                its origin at the point 0 0 0.  Its edges (other than
                hypotenuse) are 4 units long and its height is 3 units.
