General principle Reference: http://ksimek.github.io/2012/08/13/introduction/
For the target camera used when modeling 3ds Max, if you want to get its internal and external parameters, you can call $transform directly with the script function to obtain the camera external parameters.
The camera's parameters are then used to calculate the internal reference based on the camera's FOV angle (horizontal and vertical) and focal length. Http://en.wikipedia.org/wiki/Angle_of_view
First, the Width=2*f*tan (fov_h) is calculated using the Fov horizontal angle and focal length.
Using the Fov vertical angle and focal length calculation height=2*f*tan (FOV_V);
This gives the camera's imaging plane the length and width.
The pixel resolution of the rendering as the number of pixels that are longer than the width of the image, such as 640x480;
Next, calculate the focal length of the camera in pixels:
f/fx=width/640;
f/fy=height/480;
This will get the FX and FY
The center of the general image is the same as the main point, so take the image Center (320,240) as the datum point, so that the reference matrix is
[fx,0,320;
0, fy,240;
0, 0, 1];
Camera reference correlation (3ds max)