Jump to content
• Advertisement

Plane normalisation for collision detection

This topic is 2791 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi there

I am attempting to do some 3D collision detection. I am using barycentric co-ordinates with a triangle to find if a collision has occoured. However this gives false positives due to being a 2D triangle. I figured the best way around this is to do a point to plane test to figure out if a collision could occour or not.

Simply flag false if the point is not near the plane. if point<1 to plane distance and 2D barycentric = true then collision = true.

I am checking my normals with the website http://jblanco_60.tripod.com/plane.html My normals are coming out as the point-normal form as opposed to the standard form.

In standered form my normals are 1,0,0 in point form it is 40000(x-35) = 0.

In standered normal form my results are 1x + 0y + 0z - 35 = 0

my test values are {35,0,50} {35,0,-150} {35,200,-150}
This should give me a giant triangle on the wall I am testing against.

My code for calculating my normals is

float * Collision::CalculateNormal(float point1[], float point2[],float point3[],float normal[3])
{
//calcualte cross product
float ux = point2[0] - point1[0];
float uy = point2[1] - point1[1];
float uz = point2[2] - point1[2];
float vx = point3[0] - point1[0];
float vy = point3[1] - point1[1];
float vz = point3[2] - point1[2];

//float normal[3]; // calculate cross products and assign to normal

normal [0] = ((vy*uz) - (vz*uy))*-1;
normal [1] = ((vz*ux) - (vx*uz));
normal [2] = ((vx*uy) - (vy*ux));

return normal;

}

Am I using the correct cross product and entering the values right?

my Barycentric co-ordinates are

bool Collision::BarryCentricEquation(float triA[],float triB[], float triC[],float point[])
{
Collision triangle;
float v0[] = {triC[0] - triA[0],triC[1] - triA[1],triC[2] - triA[2]};
float v1[] = {triB[0] - triA[0],triB[1] - triA[1], triB[2] - triA[2]};
float v2[] = {point[0] - triA[0],point[1] - triA[1],point[2] - triA[2]};

float dot00 = Calculation::dotProduct(v0,v0);
float dot01 = Calculation::dotProduct(v0,v1);
float dot02 = Calculation::dotProduct(v0,v2);

float dot11 = Calculation::dotProduct(v1,v1);
float dot12 = Calculation::dotProduct(v1,v2);

float bcc = 1/(dot00 * dot11 - dot01 * dot01);
float u = (dot11 * dot02 - dot01 * dot12) * bcc;
float v = (dot00 * dot12 - dot01 * dot02) *bcc;

if((u>0) && (v>0) && (u+v<1))
{
triangle.bccCollision = true;
}

else
{
triangle.bccCollision = false;
}
return triangle.bccCollision;

}

Finally my point to plane equation is

float Collision::PointToPlaneTest(float pointOfInterest[],float pointOnPlane[])
{
float pointX = pointOfInterest[0];
float pointY = pointOfInterest[1];
float pointZ = pointOfInterest[2];

float planePointA = pointOnPlane[0];
float planePointB = pointOnPlane[1];
float planePointC = pointOnPlane[2];

//(planePointA*pointX) + (planePointB*pointY) + (planePointC*pointZ);

float dist = (pointX*planePointA + pointY*planePointB + pointZ*planePointC);

return dist;
}

my values enter correctly and as I head towards the plane the distance does increase but at a very slow rate. I am assuming this is because I am using my normal as 40000 and not 1?

I am calculating the distance in the main for testing currently with this
float D = (Player.directionX + 1 + Player.directionZ + A)/sqrt((B[0]*B[0]) + (B[1]*B[1]) + (B[2]*B[2]));

Would it be better to just use this in my Collsion::PointtoPlane?

Any advice would be greatly appreciated
Many thanks in advance
Phil

P.S Sorry if this is the wrong place I was nsure if this counted as math or not

[Edited by - eskimo456 on November 30, 2010 4:24:47 AM]

Share this post

Share on other sites
Advertisement

• Advertisement
• Advertisement

• Popular Contributors

1. 1
2. 2
Rutin
24
3. 3
4. 4
JoeJ
18
5. 5
• Advertisement

• 14
• 23
• 11
• 11
• 9
• Forum Statistics

• Total Topics
631767
• Total Posts
3002238
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!