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# sinbag

Member Since 05 Jan 2013
Offline Last Active Jan 13 2013 05:52 AM

### Ray Tracing: Sphere distortion due to Camera Movement

06 January 2013 - 03:09 PM

I am building a ray Tracer from scratch. My question is: When I change camera coordinates the Sphere changes to ellipse. I don't understand why it's happening. Here are some images to show the artefacts:
Sphere: 1 1 -1 1.0 (Center, radius)
Camera: 0 0 5 0 0 0 0 1 0 45.0 1.0 (eyepos, lookat, up, foy, aspect)

But when I changed camera coordinate, the sphere looks distorted as shown below:
Camera: -2 -2 2 0 0 0 0 1 0 45.0 1.0

I don't understand what is wrong. If someone can help that would be great!
I set my imagePlane as follows:

```//Computing u,v,w axes coordinates of Camera as follows:
{
Vecter a = Normalize(eye - lookat); //Camera_eye - Camera_lookAt
Vecter b = up; //Camera Up
Vecter m_w = a;
Vecter m_u = b.cross(m_w);
m_u.normalize();
Vecter m_v = m_w.cross(m_u);
}```

After that I compute directions for each pixel from the Camera position (eye) as mentioned below:

```//Then Computing direction as follows:
int half_w = m_width * 0.5;
int half_h = m_height * 0.5;
double half_fy = fovy() * 0.5;
double angle = tan( ( M_PI * half_fy) / (double)180.0 );

for(int k=0; k<pixels.size(); k++){
double j = pixels[k].x(); //width
double i = pixels[k].y(); //height

double XX = aspect() * angle * ( (j - half_w ) / (double)half_w );
double YY = angle * ( (half_h - i ) / (double)half_h );

Vecter dir = (m_u * XX + m_v * YY) - m_w ; directions.push_back(dir);
}
```

After that:

```for each dir:
Ray ray(eye, dir);
int depth = 0;
t_color += Trace(g_primitive, ray, depth);```

I have only provided the code which I think is important. But if more code snippets are required then I will provide those.