Jump to content
• Advertisement

#### Archived

This topic is now archived and is closed to further replies.

# HELP! With Moller-Trumbore ray/triangle intersection code, please!

This topic is 5347 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

I''m having trouble with the Moller-Trumbore ray/triangle alogirithm. It''s not giving me correct results, so I thought I''d try it out in a simple demo with a single triangle, ( (-1, -1, 2 ), (1, -1, 2), (0, 1, 2) ) and a ray fired from the origin (0, 0, 0), up the z-axis (0, 0, 1). Well the results I''m getting tell me that the ray is parallel to the plane of the triangle (i.e. the determinant is 0). Can someone please tell me what the stupid mistake I''m making is! V3f v0( -1, -1, 2 ); V3f v1( 1, -1, 2 ); V3f v2( 0, 1, 2 ); V3f O( 0, 0, 0 ); V3f D( 0, 0, 1 ); V3f e1 = v1 - v0; V3f e2 = v2 - v0; V3f P = D * e2; float det = e1 ^ P; float t, u, v; if ( det < 0.0000001 && det > -0.0000001 ) { cout << "Ray is in plane of polygon" << endl; return -1; } float invdet = 1/det; V3f T = ( O - v0 ); u = (T^P) * invdet; if ( u < 0.0 || u > 1.0 ) { cout << "u is outof bounds" << endl; return -2; } V3f Q = T*e1; v = (D^Q) * invdet; if ( v < 0.0 || u + v > 1.0 ) { cout << "v is out of bounds." << endl; return -3; } t = (e2^Q) * invdet; cout << "Ray intersects triangle at t = " << t << endl;

#### Share this post

##### Share on other sites
Advertisement
In your code, e1 = v1-v0 = (2,0,0) and e2 = v2-v0 = (1,2,0), so your 3x3 matrix is

(2 1 0)
(0 2 0) = M = (e1 e2 D)
(0 0 1)

and det(M) = 4. The determinant is given by D * (e1 x e2). (x is the cross product).

You computed e1 ^ (D*e2). Is ^ power? This doesn''t make much sense... You need to compute e1 x e2 (gives you a 3-vec), then D * the result.

Lutz

#### Share this post

##### Share on other sites
Thanks! You made me think to double check my operators... not my math library you see... very confusing operators for dot and cross products. Perhaps I should use the functions instead....

#### Share this post

##### Share on other sites

• Advertisement
• Advertisement

• ### Popular Contributors

1. 1
Rutin
32
2. 2
3. 3
4. 4
5. 5
• Advertisement

• 13
• 9
• 9
• 9
• 14
• ### Forum Statistics

• Total Topics
633324
• Total Posts
3011366
• ### Who's Online (See full list)

There are no registered users currently online

×

## 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!