Say I have a ray represented by a ray origin & a unit length direction
vector and
a point some-where along the ray - how do I find the distance along the
ray in the direction of the ray's direction vector from the origin  - ie
in the below diagram the distance found would be negative

ray --------------|------------------------------------->
         ^       ray
         |      origin
      point on   dist = 0
        ray
      dist = -1

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#macro Dist(RayOrigin, Direction, Point)
  ((Point.x-RayOrigin.x)/Direction.x)
#end
// supposing that 'Direction' actually is a unit vector

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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In article <3918D8BA.79E41F33@hotmail.com>, Pabs <pab### [at] hotmailcom> 
wrote:

> Say I have a ray represented by a ray origin & a unit length direction
> vector and
> a point some-where along the ray - how do I find the distance along the
> ray in the direction of the ray's direction vector from the origin  - ie
> in the below diagram the distance found would be negative

I think you are looking for the distance between two points. In POV 
scenes, just use vlength(PtA-PtB). If in a POV patch, I think there is a 
VDist() macro.
If in something else, it can be implemented like this:

double vdist(double x, double y, double z, double a, double b, double c)
{   return sqrt(sqr(x-a) + sqr(y-b) + sqr(z-c));}

Of course, you should probably use some kind of vector data type to 
simplify things.

This gives you the distance, the direction(+/-) should be pretty easy to 
figure out.

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

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On 10 May 2000 06:44:41 -0400, Warp <war### [at] tagpovrayorg> wrote:

> // supposing that 'Direction' actually is a unit vector

Or if it's not:

#macro Dist(RayOrigin, Direction, Point)
  #local Dir=vnormalize(Direction);
  ((Point.x-RayOrigin.x)/Dir.x)
#end


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG      e-mail : pet### [at] tagpovrayorg

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Peter Popov wrote:

> > // supposing that 'Direction' actually is a unit vector
>
> Or if it's not:
>
> #macro Dist(RayOrigin, Direction, Point)
>   #local Dir=vnormalize(Direction);
>   ((Point.x-RayOrigin.x)/Dir.x)
> #end
>

Will try this - actually this is for part of a patch (ParticlePatch)
Chris Huff wrote:

> I think you are looking for the distance between two points. In POV
> scenes, just use vlength(PtA-PtB). If in a POV patch, I think there is a
> VDist() macro.
> If in something else, it can be implemented like this:
>
> double vdist(double x, double y, double z, double a, double b, double c)
> {   return sqrt(sqr(x-a) + sqr(y-b) + sqr(z-c));}
>
> Of course, you should probably use some kind of vector data type to
> simplify things.
>
> This gives you the distance, the direction(+/-) should be pretty easy to
> figure out.

I tried using VDist & the result is always positive because -ve * -ve = +ve

Thanks all
Pabs

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In article <391A13E8.53BB7F05@hotmail.com>, Pabs <pab### [at] hotmailcom> 
wrote:

> I tried using VDist & the result is always positive because -ve * -ve = 
> +ve

The point direction should not be difficult to figure out...something 
like this maybe(I am tired and this is untested, so be warned):
O = ray origin(vector)
Pt = point on ray(vector)
Dir = ray direction(normalized vector)
Dist = point distance, calculated with VDist(floating point)

DBL cosA = 0;
VECTOR tmp;
VSub(tmp,Pt,O);
VNormalizeEq(tmp);
VDot(cosA, Dir, tmp);

if(cosA<0)
{   Dist *= -1;}


This basically flips the number(positive to negative) if the point and 
the direction are not on the same side of the ray. I think.

-- 
Christopher James Huff - Personal e-mail: chr### [at] yahoocom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://chrishuff.dhs.org/
TAG Web page: http://tag.povray.org/

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> This basically flips the number(positive to negative) if the point and
> the direction are not on the same side of the ray. I think.

THANKS - IT WORKS

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