"Warp" <war### [at] tagpovrayorg> wrote in message 
news:4bbebfaf@news.povray.org...
> Dre <and### [at] gmailcom> wrote:
>> "Warp" <war### [at] tagpovrayorg> wrote in message
>> news:4bbda1be@news.povray.org...
>> > Dre <and### [at] gmailcom> wrote:
>> >> Yet this does:
>> >
>> >> #declare norm = <0, 0, 0>;
>> >> #declare startPoint =<xPos, 10, zPos>;
>> >> #declare endPoint = <xPos, -10, zPos>;
>> >> trace(object, startPoint, endPoint, norm)
>> >
>> >  I don't think it does (well, not in the way you want). The third
>> > parameter
>> > of trace() specifies a direction, not an endpoint.
>> >
>> >  Probably you want the third parameter to be <0, -1, 0> because that's
>> > the direction you are shooting the rays towards.
>> >
>> > -- 
>> >                                                          - Warp
>
>> Well it does to what I want now that I changed the way I coded it to the
>> example above.  I then modified the norm as you stated but it didn't make
>> any difference at all.  Both my norm and yours are below my start point 
>> so
>> they are essentially shooting the rays in the same direction.
>
>  The normal is the *fourth* parameter. I was talking about the *third*
> parameter, which is the direction. That should be <0, -1, 0>.
>
> -- 
>                                                          - Warp

What difference does it make if its -1 or -10, they are both in the same 
plane.

Or are you saying the 3rd parameters is a direction vector not a final end 
point vector?

Cheers Dre

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