rotate_extrude
As for <linear_extrude>, the <rotate_extrude> operator “extrudes” a set of 2d shapes into a solid. By convention, it does so by rotating the 2d profile around the global Y-axis. No solid may occur in the set of input shapes.
| Parameter name | Description | Status |
|---|---|---|
| angle | Rotation angle [radians] around Y | required |
| pitch | offset in Y per revolution | optional (default=0.0) |
By convention, the 2d profile exists the xy-plane with z=0.0. To avoid self-intersection and ensure properly oriented faces in the result, the profile must be positioned so that that all x-coordinates are positive. The rotation angle shall be specified as positive (a positive rotate_extrude angle corresponds to a negative right hand rule rotation around the Y-axis).
Different combinations of angle and pitch have the following interpretations:
| case | angle | pitch | interpretation |
|---|---|---|---|
| 1 | < 2*PI | 0.0 | The result is a “cake slice” |
| 2 | >= 2*PI | 0.0 | The result is a full torus |
| 3 | > 0.0 | > 0.0 | The result is a spiraling thread, reverse threaded |
| 4 | > 0.0 | < 0.0 | The result is a spiraling thread, normal threading |
case 1 : Using rotate_extrude on a transformed square
<?xml version="1.0" encoding="utf-8"?>
<xcsg version="1.0">
<rotate_extrude angle="1.0471975511965976" pitch="0">
<square size="10" center="false">
<tmatrix>
<trow c0="0.70710678118654757" c1="-0.70710678118654746" c2="0" c3="30"/>
<trow c0="0.70710678118654746" c1="0.70710678118654757" c2="0" c3="0"/>
<trow c0="0" c1="0" c2="1" c3="0"/>
<trow c0="0" c1="0" c2="0" c3="1"/>
</tmatrix>
</square>
</rotate_extrude>
</xcsg>
case 2 : Same as above, but rotated 2*PI, results in full torus
case 3 : Same as above, but rotated 6*PI combined with a negative pitch of -15 per revolution
