PhotoModeler needs to know the focal length, principal point and digitizing scale of a camera before it can produce 3D models from that camera. If you know these parameters relatively well, and you are not concerned with the highest measurement accuracy, you may achieve a reasonable result. However, a calibration strongly recommended.
Certain paths in the New Project Wizard allow you to select a camera source. If you do not have a calibration for the camera, there are ways to set up an approximate camera, either with ‘standard’ default settings, or using the EXIF information stored in an image. You can also use the auto-calibration feature when setting up a SmartPoints Project.
You can create an approximate (non-calibrated camera) directly in PhotoModeler using the Add button on the Camera Viewer Dialog. You will not get the most accurate measurement results, but it may be all you need. Often the results with an approximate camera can be quite good but sometimes the results are un-usable – it depends on the quality of input information.
If you find your estimates for the camera parameters do not produce good 3D models in PhotoModeler or if you are interested in the highest measurement accuracy, you will need to calibrate your camera.
You usually need to calibrate a camera:
• before the first time it is used in PhotoModeler,
• when you use a different lens on the camera,
• when you switch between two different focal settings on the camera (i.e. a camera with a zoom lens has multiple focal lengths - you need separate calibrations for this camera if you wanted to use different focal settings). Note that you cannot normally calibrate a camera with a zoom lens at an intermediate setting because it is not exactly reproducible. For zoom lenses only calibrate at most-wide angle, or most telephoto.
• when the camera or lens has been badly damaged and has been rebuilt.
If you use just one camera and one fixed focal-setting lens for all your projects, you will need to do only one calibration and perhaps never have to calibrate it again. If you use several lenses, then you will need to calibrate each of the lenses.
Note: for projects that have good camera angles and overlap, an auto-calibration or field-calibration may suffice or may even be superior to pre-calibration.