# 3-D Graphics

``` BBS: Inland Empire Archive
Date: 05-01-92 (23:32)             Number: 179
From: RON MCDERMOTT                Refer#: NONE
To: RICH GELDREICH                Recvd: NO
Subj: 3-D Graphics                   Conf: (2) Quik_Bas```
```Rich,

RG>What we need:
RG>A point, outside of the plane, that is perpendicular to the
RG>plane when a line is drawn from the point through the middle
RG>of the plane. The point also has to be certain distance from
RG>the plane (64 units or so). We need the X, Y, & Z coordinates
RG>of this point.

Not sure if this would help, but one test for perpendicularity
is a dot product of the two vectors defined by the two lines to
be tested.  This would involve defining a line drawn from one of
the corners, passing through the center point, and calculating
the change in x, y, and z values.  The resulting differences are
then the coefficients of a vector in i,j,k format.  The second
vector would be the one passing through the center point and the
point external (which is unknown).  The delta x of the first vector
times the delta x of the unknown vector, added to the product of
the delta y's, added to the product of the delta z's must equal
zero.

For example, consider a corner of 1,1,1;  a center point of
3,4,5; and an unknown point out of plane of x,y,z.....
(3-1)*(x-3) + (4-1)*(y-4) + (5-1)*(z-5) = 0 .  You'd need other
information to solve, but this might be one piece to add to the
puzzle!?

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