# Thread: Frustum problems - URGENT!

1. ## Frustum problems - URGENT!

hey all,

How can I find out focal length - f, and chosen dimension - d (see attachment). I need them to find alpha(angle of frustum)

Or if you know better way to find out angle using intrinsic parameters, I will be happy))

2. Didn't you ask for urgent help on this before?

3. yes , and don't got full answer for that, and thought it would be better to reformulate my question!

4. I gave you "the full answer", but obviously you didn't understand. If you remains silent it assumes you are satisfied with the answer.
The formula you found on Wikipedia is exactly the same I gave you; except I divided focal length into two components: minimal focal length and zoom factor.
Focal length and sensor dimensions are not the values you can choose! You have to check a datasheet for the particular camera to get correct values.
For example: standard 1/2.5" sensor is 5.8 x 4.4 mm. In OpenGL you are setting vertical FOV, so the height is used in the formula. The previous sensor has 4:3 aspect, so you also need to obey this restriction if you need 1:1 mapping in your window.

Before going any further (except you want empirically determine all those values), find out a detailed specification of the sensor used in your camera, and pay attention to the following parameters:
- aspect
- sensor dimensions
- minimal and maximal focal length

5. 6.716550e+001 3.265328e+000 -6.422589e+000;
0.000000e+000 -7.718194e+001 -3.809459e+001;
0.000000e+000 0.000000e+000 -1.066025e-001

This is my matrix of intrinsic parameters of the camera. And I have no parameter you mentioned(focal length,Sensor size...).
And the chalange is how to estimate them.

6. What's the meaning of those parameters?

1. What is a camera calibration? (Do you have a physical camera or a mathematical model?)

2. What do you actually have to do? (If it is a physical camera, it have sensor and lens.)

3. What are "intrinsic" and "extrinsic" parameters?

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