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## [help-3dldf] Re: [metafont] Re: button-hole problem

**From**: |
Laurence Finston |

**Subject**: |
[help-3dldf] Re: [metafont] Re: button-hole problem |

**Date**: |
Sat, 23 Apr 2005 20:01:50 +0200 |

**User-agent**: |
IMHO/0.98.3+G (Webmail for Roxen) |

>* Ah, so if I understand well, you are using parallel projection?*
>* This is indeed a special case of projective projection, where the*
>* "eye" point is far away (strictly speaking: at infinity).*
I have implemented perspective projection using a `Focus' and parallel
projection onto the three major planes. For example:
focus f;
set f with_position (-5, 5, -10) with_direction (-5, 5, 10)
with_distance 10;
picture p;
beginfig(1);
circle c;
c := unit_circle scaled 2 rotated (15, 30, 60);
draw c;
p := current_picture;
endfig with_focus f; %% perspective projection is the default.
beginfig(2);
output p with_projection parallel_x_y;
endfig;
beginfig(3);
output p with_projection parallel_x_z;
endfig;
beginfig(4);
output p with_projection parallel_z_y;
endfig;
Laurence