> Inspired by fiddling around with height fields tonight.
>
> My question is ...
>
> Can someone help me figure out how to use trace and the normal
> vector that is set by the function to place my trees only in those
> places that are at a certain level of flatness?
>
> Is such a thing possible?
>
> Thanks ...

First of all, nice pic.

Concerning trace, try this:

You should declare your heightfield
#delcare HF_Object=
heightfield......

and your tree
#declare Tree=
...........

and then you can declare your tree-array
#declare Tree_Array=
 union{
  #declare A=0;
   #while (A<=20) //change this set the amount of trees in this direction
   #declare B=0;
    #while (B<=20) //change this set the amount of trees in the other
direction
     #declare Normal=<0,0,0>;
     // when you want to change the distance between the trees change
     // this < 1+2*B , 0 , 1+2*A > maybe to this < 1+4*B , 0 , 1+4*A >
     // whatever you want
     #declare Pos=trace(HF_Object, < 1+2*B , 0 , 1+2*A > + y*20, <0,-1,0>,
Normal);
     #if (vlength(Normal))
     // I declare the materials often in extra files, when the scene becomes
too big.
      object {Tree material{Tree_Material} translate Pos}
     #end
     #declare B=B+1;
    #end
    #declare A=A+1;
   #end
 }

object{HF_Object}
object{Tree_Array}

You can also randomize the placing of the trees a bit, by adding a random
value to the translation string.

Regards,
flo

--

DigitalTwilight
#homepage: http://www.digitaltwilight.de
#email: kin### [at] gmxnet


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