**comp.graphics.algorithms**

## Subject: **Re: Basic perspective/normal q**

"Hans-Bernhard Broeker"

news:4bkt8rF123r6gU1@news.dfncis.de...

> [jongware]

>

> > I know it's no good -- that's why I get substandard results. Can you

> > substantiate your comment with the required math? All inputs are as

> > mentioned: a number of x,y,z coordinates for a plane; its normal; a

camera

> > position. I guess that's all what it takes for input.

>

> If anything, it's too much. All you really need is the 'd' parameter

> for the plane's normal equation:

>

> plane = { P | P.N = d }

>

> Any of those "x,y,z coordinate" triplets should do. Call it P0,

> the reference for that plane, and the normal equation can be

> rewritten:

>

> (P-P0).N = 0

>

> The test you have to make is on the sign of the left hand side of this

> equation, with the camera position for 'P'. If it's positive, that

> means the point is on that side of the plane the normal points out,

> i.e. the plane is visible. Otherwise you're looking at it's back

> side.

A generous tip'o the hat to Hans-B: I got it working by finally plugging the

*correct* values into this very formula.

Let's call it my learning curve (the phrase "North Face of the Eiger" may

spring to mind).

[jw]

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