HPIPE                                                              Menu: PRISM
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Creates an open semi-cylindrical prism or a (2D) semi-annulus polygon.

        1. * (CHAR) plane of base semi-annulus (x-xy, y-yz,z-zx) <x>
        2. * (NUM) option: (0-top half /3-right half /6-bottom half /9-left
                   half) <0>
        3. * (POINT) center of radius
        4. * (NUM) outer radius of semi-annulus (greater than 0)
        5. * (NUM) "wall" thickness (greater than 0)
     for option `x':
        6. * (NUM) height of prism
     for option `y' or `z':
        6. * (NUM) length of prism
     for all options:
        7. * (Y/N) positive prism? <y>

Description:
This command creates a (2D) semi-annulus polygon or an open semi-cylindrical
prism (half pipe).
Specify the base plane (one of the axial planes; x  xy plane, the default, y
yz plane or z  xz plane).
Choose one of the options for semi-cylinder orientation: 0  top half, 3  left
half, 6  bottom half, or 9  right half (the default is 0).
Define the radius center point, the outer radius and the "wall" thickness.
Specify the height (for option `x') or the width (for options `y' or `z'). You
may enter `0' for a 2D polygon. Specify whether the resulting solid is to be
positive (option `y', the default) or negative (option `n').
You are prompted to create additional semi-cylinders until another command is
selected.
        Example: \hpipe x 0 3 3 0 4 0.2 1 y
        Result:  A positive semi-cylinder is created with its center point at
                 3 3 0, a radius of 4 units (meters or feet), a "wall"
                 thickness of 0.2 units and a height of 1 unit.
