Away3D Forum point in triangular mesh

jagguy, Newbie
Posted: 18 June 2011 09:24 AM Total Posts: 27

hi,

I have a half cube shape mesh (3D right angled triangle shape) and is there a way to detect if a point lies inside this shape?

I can easily if a point lies inside its 3D bounding box but I need to test if the point lies inside the object.

in flash 2d you have a way to detect alpha.

Stephen Hopkins, Sr. Member
Posted: 18 June 2011 11:41 AM Total Posts: 110 [ # 1 ]

You can do this for each face in the mesh:
http://forums.anandtech.com/showthread.php?t=162930

If all the dot products are negative, then its inside your mesh (assuming your mesh normals face outwards)

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jagguy, Newbie
Posted: 18 June 2011 12:50 PM Total Posts: 27 [ # 2 ]

i really need to see an example.

I just need to test on the sloping face of the mesh and a point.

i just spent 2 hours on vector math hell with a line and point and in the end the mathematics didnt work

Stephen Hopkins, Sr. Member
Posted: 18 June 2011 09:19 PM Total Posts: 110 [ # 3 ]

var testPoint:Vector3D = ...
for each face in mesh
 var normal:Vector3D = face.normal;
 var position:Vector3D = face.v0;
 //the plane and the testPoint need to be in the same space, this moves the plane to the origin
 //the transformedPoint is now relative to the plane
 var transformedPoint:Vector3D = testPoint.subtract(position);
 var dot:Number = transformedPoint.dotProduct(normal);
 if(dot >= 0)
  //point on plane, or on same side of normal
 else 
  //point on opposite side of normal 

You are gonna have to figure out how to get faces, vertices, and normals.

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http://www-scf.usc.edu/~shopkins

jagguy, Newbie
Posted: 19 June 2011 03:52 AM Total Posts: 27 [ # 4 ]

looks like I am doing everything manually.

i will find the suface that is on a slope for right angled triangle 3d Shape (the longest side).

now the slope is at a 45 deg angle .

4 points around this rectangle surface is
A(0,0,0)
B(200,0,0)
C(200,71,71)
D(0,71,71)

V1 vector1= B - A (200,0,0)
V2 vector2=C - A (200,71,71)

cross product vector1 X vector2

cross product x= v1.y X v2.z - v1.zX v2.y = 0X71 - 71X0= 0
cross product y= - (( v2.z X v1.x) - (v2.x X v1.z)) = - 71X200 -0= -14200
cross product z= v1.x X v2.y - v1.y X v2.x= 14200

(0,-14200,14200) is normal so normalize i get

20081 = normalize factor

(0, -.707, .707) = normal vector for this shape

now since y value is negative the normal points down but i want it to point up dont I out of the surface?

Stephen Hopkins, Sr. Member
Posted: 19 June 2011 07:30 AM Total Posts: 110 [ # 5 ]

swap v1 and v2 in your cross product

If you have an actual away3d mesh, there should be a way to access vertex data or faces, at least there was a way in 3.6, not sure about in broomstick.

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Alejandro Santander, Administrator
Posted: 19 June 2011 07:40 AM Total Posts: 414 [ # 6 ]

I have an article on OBB on my site that might help: http://www.lidev.com.ar/obb-collision-detection/
obb = oriented bounding box
aabb = axis aligned bounding box

What matters to you is the method of separating axes.

point in triangular mesh Software: Away3D 3.x

jagguy, Newbie Posted: 18 June 2011 09:24 AM Total Posts: 27 hi, I have a half cube shape mesh (3D right angled triangle shape) and is there a way to detect if a point lies inside this shape? I can easily if a point lies inside its 3D bounding box but I need to test if the point lies inside the object. in flash 2d you have a way to detect alpha.
Stephen Hopkins, Sr. Member Posted: 18 June 2011 11:41 AM Total Posts: 110 [ # 1 ] You can do this for each face in the mesh: http://forums.anandtech.com/showthread.php?t=162930 If all the dot products are negative, then its inside your mesh (assuming your mesh normals face outwards) Signature http://www-scf.usc.edu/~shopkins
jagguy, Newbie Posted: 18 June 2011 12:50 PM Total Posts: 27 [ # 2 ] i really need to see an example. I just need to test on the sloping face of the mesh and a point. i just spent 2 hours on vector math hell with a line and point and in the end the mathematics didnt work
Stephen Hopkins, Sr. Member Posted: 18 June 2011 09:19 PM Total Posts: 110 [ # 3 ] var testPoint:Vector3D = ... for each face in mesh var normal:Vector3D = face.normal; var position:Vector3D = face.v0; //the plane and the testPoint need to be in the same space, this moves the plane to the origin //the transformedPoint is now relative to the plane var transformedPoint:Vector3D = testPoint.subtract(position); var dot:Number = transformedPoint.dotProduct(normal); if(dot >= 0) //point on plane, or on same side of normal else //point on opposite side of normal You are gonna have to figure out how to get faces, vertices, and normals. Signature http://www-scf.usc.edu/~shopkins
jagguy, Newbie Posted: 19 June 2011 03:52 AM Total Posts: 27 [ # 4 ] looks like I am doing everything manually. i will find the suface that is on a slope for right angled triangle 3d Shape (the longest side). now the slope is at a 45 deg angle . 4 points around this rectangle surface is A(0,0,0) B(200,0,0) C(200,71,71) D(0,71,71) V1 vector1= B - A (200,0,0) V2 vector2=C - A (200,71,71) cross product vector1 X vector2 cross product x= v1.y X v2.z - v1.zX v2.y = 0X71 - 71X0= 0 cross product y= - (( v2.z X v1.x) - (v2.x X v1.z)) = - 71X200 -0= -14200 cross product z= v1.x X v2.y - v1.y X v2.x= 14200 (0,-14200,14200) is normal so normalize i get 20081 = normalize factor (0, -.707, .707) = normal vector for this shape now since y value is negative the normal points down but i want it to point up dont I out of the surface?
Stephen Hopkins, Sr. Member Posted: 19 June 2011 07:30 AM Total Posts: 110 [ # 5 ] swap v1 and v2 in your cross product If you have an actual away3d mesh, there should be a way to access vertex data or faces, at least there was a way in 3.6, not sure about in broomstick. Signature http://www-scf.usc.edu/~shopkins
Alejandro Santander, Administrator Posted: 19 June 2011 07:40 AM Total Posts: 414 [ # 6 ] I have an article on OBB on my site that might help: http://www.lidev.com.ar/obb-collision-detection/ obb = oriented bounding box aabb = axis aligned bounding box What matters to you is the method of separating axes.

point in triangular mesh

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