"Tim McMurdo" <jod### [at] wohrrcom> wrote in message 
news:web.4362358e2d40991cacb32c570@news.povray.org...
>I have a gun port cut into the hull of the ship. The port was created by
> differencing a box from the hull. The box was created along the z axis and
> is 900mm wide (+450 and -450 on the x axis). The box was then rotated 15
> degrees on the y axis and translated to <12350,0,0>.
>
> I need to use the trace function to locate the points on the hull that are
> 451mm either side of the center of the gunport opening.
>
> 1. What is the math involved in determining the angle from the z axis to 
> the
> points on either side of the opening? Do I shoot a trace at the center
> first to determine the distance from <12350,0,0,0> to the center and then
> use C2 = A2 + B2 and trig to figure the angles to the points on either
> side?
>
> 2. Once I have the angle, how do I convert it to a vector that I can use 
> in
> trace?
>
> Thanks,
>
> Tim
>

Hi Tim,

You could certainly do what you describe and perform the calculations (for 
the second part look up vrotate() in help)

But if I wanted to find points on either side of the such an opening, I'd 
tend to be lazy and let POV-Ray do the work.
If you just assign your tranformation a name, then you can apply it to your 
box and also to a couple of points that you can then use to fire rays 
parallel to the transformed line of the box and 451 units from its centre.

For example:

#include "transforms.inc"

#declare YourTransform = transform {rotate y*15 translate 12350*x};
#declare YourHull = difference {
  plane {-z, 100 pigment {color rgb <1,0,1>}}
  box {<-450,-450,-450><450,450,450> transform YourTransform pigment {color 
rgb <1,1,0>}}
}

#declare LeftNormal = <0,0,0>;
#declare LeftStartPoint  = vtransform(<-451,0,-500>, YourTransform);
#declare LeftTarget      = vtransform(<-451,0, 500>, YourTransform);
#declare LeftPosition = trace(YourHull, LeftStartPoint, 
LeftTarget-LeftStartPoint, LeftNormal);
#if (vlength(LeftNormal)!=0)
  #debug concat("Left point: ",vstr(3,LeftPosition,",",3,3),"\n")
#else
  #debug "Whoops. Missed on Left!"
#end

#declare RightNormal = <0,0,0>;
#declare RightStartPoint  = vtransform(< 451,0,-500>, YourTransform);
#declare RightTarget      = vtransform(< 451,0, 500>, YourTransform);
#declare RightPosition = trace(YourHull, RightStartPoint, 
RightTarget-RightStartPoint, RightNormal);
#if (vlength(LeftNormal)!=0)
  #debug concat("Right point: ",vstr(3,RightPosition,",",3,3),"\n")
#else
  #debug "Whoops. Missed on Right!"
#end

camera {location vtransform(<0,100,-1700>,YourTransform) look_at 
vtransform(<0,0,0>,YourTransform)}
light_source { <12000, 1000, -2000> color rgb 1}
object {YourHull }
sphere   {LeftPosition,20 pigment {color rgb <1,0,0>}}
cylinder {LeftStartPoint,LeftTarget,10 pigment {color rgb <0,1,1>}}
sphere   {RightPosition,20 pigment {color rgb <1,0,0>}}
cylinder {RightStartPoint,RightTarget,10 pigment {color rgb <0,1,1>}}


Regards,
Chris B.

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