Before 3D computation, the initial values must be entered for camera location and look-at direction (Tx, Ty, Tz, Rx, Ry, Rz). The initial values need not to be accurate. Photo4D will compute accurate values for these parameters.
Photo4D can usually compute a meaningful result using the default values for other parameters.
Some parameters are more difficult for Photo4D to compute than others. Tx/y/z and Rx/y/z are the easiest to compute. Therefore, there is no need to measure the accurate camera location during photographing.
The focal length F and distortion factor K need more reference points to be computed accurately. Since reference points are generally difficult to obtain, it is always a good practice to write down the focal length F while taking picture. For a fix length lens, the number on the lens can be used directly, e.g., 35mm, 38mm, or 50mm for a standard lens. If a zoom lens is used, the focal length can usually be read from the lens position.
In addition, The accuracy of 3D computation is not sensitive to the values of focal length F. Up to 20% of errors in the value for F may not have a noticeable effect on accuracy.
The imaging plane width (W) should be set correctly. The default value for W is 30mm. User should find out this value for their camera. Photo4D cannot compute this value.
The pixel aspect ratio (A) needs even more reference points to be computed. Fortunately, it should be 1.0 for most cameras.