[Dir3d-l] Line-Plane intersect

[ullala]

At 11:15 Uhr +0000 17.3.2003, Phillip Gan wrote:
>Does anybody know of a Lingo command that will find the point of 
>intersection between a line and a plane? I want a model to appear on 
>a plane at a position determined by a click. The 
>spriteSpaceToWorldSpace command puts the model somewhere way off 
>into the distance. I haven't been able to find a command that does 
>what I want, but intersections are a pretty fundamental idea in 3D 
>maths so I reckon I must be missing something obvious.

I wrote 2 handlers a few days ago for a generic, mathematical 
ray-plane-interesection calculation...
Till now it looks like its working without mistakes ;-)

Well, if anybody knows a better way, please let me know.


First handler is the ray-plane-intersection, while the plane is 
defined by its normal and the distance to (0,0,0) in the world 
(Koordinatenursprung in engl.?)
If you dont know this distance but a point on the plane instead, you 
can get the distance with the second handler.

Take care about line breaks...

-- *********************************** --

on RayPlaneIntersection RayPoint, RayVector, PlaneNormal, PlaneDistance
   -- calculating intersection point of ray and plane
   -- returns intersection  point (vector) if it exists
   -- returns void if ray is parallel to plane (within plane or not)

   -- RayPoint  ... point on ray
   -- RayVector ... ray direction (normalized!)
   -- PlaneNormal   ... normal vector to plane (normalized!)
   -- PlaneDistance ... distance from plane to Koordinatenursprung

   -- angle between ray and normal
   tAngle = RayVector.angleBetween(PlaneNormal)
   if abs(tAngle) = 90 then RETURN -- ray parallel

   -- shortest distance between rayPoint and plane
   a = RayPoint.angleBetween(PlaneNormal)
   deltaD = PlaneDistance - (cos(a*pi()/180.0) * RayPoint.magnitude)

   -- distance from rayPoint to intersection
   D = deltaD / cos(tAngle*pi()/180.0)

   RETURN RayPoint + (D*RayVector)
end

-- *********************************** --

on GetPlaneDistance PlanePoint, PlaneNormal
   -- calculating distance from plane to Koordinatenursprung
   -- PlanePoint  ... a point (vector) on the plane
   -- PlaneNormal ... normal vector to plane (normalized!)

   distP = PlanePoint.magnitude
   if distP = 0 then RETURN 0
   tAngle = PlanePoint.angleBetween(PlaneNormal)
   if abs(tAngle) = 90 then RETURN 0
   D = abs(distP * cos(tAngle*pi()/180.0))
   SP = D * PlaneNormal
   if (SP-PlanePoint).magnitude > (-SP-PlanePoint).magnitude then D = -D
   RETURN D
end

-- *********************************** --

ullala :-)

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