On Tue, 04 Dec 2001 07:06:15 -0500, "Timothy R. Cook"
<tim### [at] scifi-fantasycom> wrote:

>I still don't quite get why math (and hence POV) 3D coords use
>left-hand rule; apart from most people being right-handed, CAD
>programs use right-hand, being based on architectural design which
>draws a floorplan along the XY plane with Z being the elevation,
>which is what you get when you draw a floorplan on a standard
>cartesian grid with 0,0 being the origin in the lower-left.

3D computer graphics were first employed in maths where x points to
the right and y up (as on a blackboard, drawing board etc.) The
direction of z was chosen the way it is (away from user) so that with
the origin in the lower-left corner, all coordinates of visible points
in pseudo-perspective (axonometry?) are positive, therefore easier to
deal with.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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