Calculating direction of car from normal vector and angle
For an assignment, I have to program a racing game
At the moment I try calculating the angle from the normal vector to the surface and the rotation angle.
I am trying to use the formula for the rotation from http://www.euclideanspace.com/maths/alge.../index.htm
As the 'forward' vector is (0, 0, 1), it should just be a matter of taking the last column?
The angle is expressed as the angle between the normal and the y axis.
Where d is the direction vector (shown by green) and n is the normal vector for the car (shown by blue)...
Anyway, when I draw the (scaled) direction vector I get what you see below. The green line should point straight ahead, parallel to sides of the car's bounding box. It works when the car is on the flat, but then goes funny when it is on a hill, although as you can see the bounding box and the normal vectors look correct.
It isn't a issue with degrees/radians as angles are stored as radians....
Special thanks to those who helped with my last question, you can see the background image being used!
At the moment I try calculating the angle from the normal vector to the surface and the rotation angle.
I am trying to use the formula for the rotation from http://www.euclideanspace.com/maths/alge.../index.htm
As the 'forward' vector is (0, 0, 1), it should just be a matter of taking the last column?
The angle is expressed as the angle between the normal and the y axis.
Code:
float theta = acos(myCar>n[1]) + myCar>orientation>y;
myCar>d[0] = (myCar>n[1] * sin(theta) + (1cos(theta))*myCar>n[2]*myCar>n[0]);
myCar>d[1] = (myCar>n[0]*sin(theta) + (1cos(theta))*myCar>n[1]*myCar>n[2]);
myCar>d[2] = (1+ (1cos(theta))*(myCar>n[2]*myCar>n[2]1));
Where d is the direction vector (shown by green) and n is the normal vector for the car (shown by blue)...
Anyway, when I draw the (scaled) direction vector I get what you see below. The green line should point straight ahead, parallel to sides of the car's bounding box. It works when the car is on the flat, but then goes funny when it is on a hill, although as you can see the bounding box and the normal vectors look correct.
It isn't a issue with degrees/radians as angles are stored as radians....
Special thanks to those who helped with my last question, you can see the background image being used!
I doubt this is the 'correct' way to do it, but I'd do something crazy like this:
1) call glPushMatrix to save the current matrix
2) glLoadIdentity, then call the glRotates that you use to rotate the car model into position
3) use glGetFloatv(GL_MODELVIEW_MATRIX, mat) to store the current OpenGL matrix
4) Take a (0, 0, 1) vector and multiply it by that matrix.
5) glPopMatrix to restore the settings
That should make the vector point forward from the front of the car. There are probably faster ways, though  I just wanted to show one way that should work.
1) call glPushMatrix to save the current matrix
2) glLoadIdentity, then call the glRotates that you use to rotate the car model into position
3) use glGetFloatv(GL_MODELVIEW_MATRIX, mat) to store the current OpenGL matrix
4) Take a (0, 0, 1) vector and multiply it by that matrix.
5) glPopMatrix to restore the settings
That should make the vector point forward from the front of the car. There are probably faster ways, though  I just wanted to show one way that should work.
Possibly Related Threads...
Thread:  Author  Replies:  Views:  Last Post  
Formula for converting angle to vector?  komirad  2  14,099 
Jul 29, 2011 07:29 AM Last Post: ThemsAllTook 

Direction of normal  Miglu  3  5,236 
Oct 4, 2010 05:08 PM Last Post: Skorche 

Question Regarding the Reflect Angle of a Transition  iBaby  3  5,364 
Apr 27, 2010 03:15 PM Last Post: JustinFic 

Direction formula?  TimMcD  2  7,304 
Nov 11, 2009 11:42 PM Last Post: TimMcD 

ending location from angle and speed  Kazooless  5  6,718 
Apr 3, 2009 02:40 PM Last Post: Gillissie 