Camera calibration is the process of finding the true parameters of the camera that took your photographs. Some of these parameters are focal length, format size, principal point, and lens distortion.
Imagine building a deck on your house using a tape measure that showed 10 inches for the first foot and 13 inches for the second foot. The deck that resulted would be the wrong size and might not even stand up! It is the same with photogrammetry and your camera. If the software does not know the true camera parameters you will get poor results or no results at all.
How accurate do the camera parameters need to be? The answer depends on how you use your PhotoModeler results. Sometimes good guesses or approximate values for the parameters are good enough (they do have to be close to the correct values). If you need high accuracy though, completing a camera calibration is very important.
How difficult is camera calibration? Calibration is not difficult but requires some care to complete one properly. PhotoModeler provides a number of ways to do camera calibration. The standard method is to use the included Camera Calibrator program, which creates a file containing the camera parameters. This file can then be used in all PhotoModeler projects where photos are taken by that particular camera. The camera only has to be calibrated once for a given focal length. In most cases, the wide angle setting works best for a reasonable range of distances and object sizes.
You can also use PhotoModeler to do field calibrations, self-calibrations or Inverse Camera. For great results, you can also purchase a pre-calibrated camera from Eos Systems when you buy PhotoModeler. (Due to the camera manufacturer’s warranty, the cameras are only available to North American customers.)