"Dre" <and### [at] gmailcom> schreef in bericht 
news:4bbd517d$1@news.povray.org...
> "Dre" <and### [at] gmailcom> wrote in message 
> news:4bbd2f59$1@news.povray.org...
>> Hi, as the title states, can you use the trace command on a heightfield?
>>
>> I've been trying and trying and I cant get it to work.  I've successfully 
>> used the trace() command on isosurfaces and simple boxes, spheres but I 
>> cant for the life of me get this to work.
>>
>> Just wondering if this actually does work or I'm barking up the wrong 
>> tree!
>>
>> Cheers Dre
>>
> Nevermind, I worked it out, that trace command has some weirdness about 
> it.
>
> This doesn't work:
>
> #declare norm = <0, 0, 0>;
> trace(object, <xPos, 10, zPos>, <xPos, -10, zPos>, norm>)
>
> Yet this does:
>
> #declare norm = <0, 0, 0>;
> #declare startPoint =<xPos, 10, zPos>;
> #declare endPoint = <xPos, -10, zPos>;
> trace(object, startPoint, endPoint, norm)
>
> Unless I'm doing something wrong, that seems broken to me...
>


No, trace() is not broken. The following always works for me, with whatever 
object as target:
    #declare Norm =  <0, 0, 0>;
    #declare Start = <my.x, 10, my.z>;
    #declare Pos = trace (Obj, Start, -y, Norm);

Start must be above the object, so adapt the y value; -y indicates the 
direction of tracing.

Thomas

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