Oh well, I did it. The trig formula is used when rotating the object. But
I've not got any problem with it.

jrg.

"Ron Parker" <ron### [at] povrayorg> ha scritto nel messaggio
news:slr### [at] fwicom...
> On Sat, 7 Jul 2001 14:29:53 +0200, JRG wrote:
> >If you want to know the y coordinate of a point (i.e. its height):
> >
> >#local _alt=vdot(y,trace( land, temp_pos+10000*y,-y));  // check the
> >altitude
> >
> >or, even easier:
> >
> >#local _alt=(trace( land, temp_pos+10000*y,-y)).y;  // check the altitude
> >
> >(I didn't check if the last notation works, but it should).
> >
> >Where land is the landscape object,
> >temp_pos is the coordinate (of XZ plane) you want to check (you are
supposed
> >to not use landscapes higher than 10000 units...).
> >
> >For normal calculation things are slightly more complicate (even if it's
> >just another line of trig formulae).
>
> You shouldn't need another line of trig.  You should be able to do:
>
> #local _norm = <0,0,0>;
> #local _alt=trace(land, temp_pos+10000*y,-y,_norm).y;
>
> and find the normal at the intersection in the _norm vector (or <0,0,0> if
> no intersection was found.)
>
> --
> #local R=<7084844682857967,0787982,826975826580>;#macro
L(P)concat(#while(P)chr(
> mod(P,100)),#local P=P/100;#end"")#end background{rgb 1}text{ttf
L(R.x)L(R.y)0,0
> translate<-.8,0,-1>}text{ttf
L(R.x)L(R.z)0,0translate<-1.6,-.75,-1>}sphere{z/9e3
> 4/26/2001finish{reflection 1}}//ron.parker@povray.org My opinions, nobody
else's

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