class vec3f
{
    ...
    public:
    float x, y, z;
    void Normalize();  //norm to 1
    void RotateBy(float fltAngle, float _x, float _y, float _z); //rot by an arbitrary axis
};

class Buggy
{
    ...
    public:
    vec3f position;
    vec3f heading;
    float velocity;
    void Draw() 
    {
        glPushMatrix();
        glTranslatef(position.x, position.y, position.z);
        glRotatef(heading.x, 0, 1, 0);
        glRotatef(heading.y, 1, 0, 0);
        glRotatef(heading.z, 0, 0, 1);

        //draw the object
        ...

        glPopMatrix();
     }

     void UpdatePosition()
     {
         if (velocity > GROUND_FRICTION)
         {
            velocity-=GROUND_FRICTION;    //Slow the buggy with friction
         }

         //Now update its position
         heading.Normalize();
         position += heading * velocity;

         //And find position.y using interpolated heightmap data...
         //this bit works.  trust me.
         ...
     }


};

//And in the keyboard callback
...
//hit some key to make it turn
TheBuggy->heading.RotateBy(amount, 0, 1, 0);  //rotate around the y axis

void vec::RotateBy(float fltAngle, float fltX, float fltY, float fltZ){float theta = fltAngle * PI/180.0f;/* Multiply this vector { this.x, this.y, this.z, 1.0f }bytX^2+c    tXY+sZ  tXZ-sY  0tXY-sZ    tY^2+c  tYZ+sX  0tXY+sY    tYZ-sX  tZ^2+c  00         0       0       1where XYZ are fltX, fltY, fltZ - the axis to rotate about*///Calculate the perpendicular component: multiply this by the cosine of the rotation anglevec vecPerp = vec( this->x, this->y, this->z) * cos(theta);//Calculate the cross-product between the rotation axis and this vector//vec operator*(vec other) has been overloaded to cross product.vec vecCross = vec(fltX, fltY, fltZ)*vecPerp;//Add the two togethervec r = vecPerp + vecCross;//Add the component of the vector we're about to rotate that is parallel to the rotation vector//TODO - unsure about this step.float c = cos(theta);float s = sin(theta);float t = 1.0f-cos(theta);//for readability's sake.float X2 = fltX * fltX;float Y2 = fltY * fltY;float Z2 = fltZ * fltZ;float XY = fltX*fltY;float XZ = fltX*fltZ;float YZ = fltY*fltZ;vec rot;rot.x =  (r.x * (t*X2)+c)+(r.y * (t*XY ) + s*fltZ )+(r.z * (t*XZ) - s*fltY);rot.y = (r.x * (t*XY)-s*fltZ)+(r.y * (t*Y2)+c)+(r.z * (t*YZ) + s*fltX);rot.z = (r.x * (t*XY)+s*fltY)+(r.y * (t*YZ) - s*fltX )+(r.z * (t*Z2) + c);//All done, now apply the rotation to this.this->x = rot.x;this->y = rot.y;this->z = rot.z;}