The type of tracking used will depend on the nature of the targets and the project. There are three stages to tracking: the initial placement in the image, the search, and the sub-pixel marking.
The initial placement can be done two ways: 2D-same and 3D projection. In 2D-same placement, the 2D location of the mark in the previous epoch is used in the epoch being tracked. In 3D projection, the 3D location of the point is projected onto the photograph being tracked and that 2D location is used as the initial position.
There are 2 types of 3D tracking '3D (all photos)' and '3D (previously marked)': the (all photos) option will try to track every 3D point on every photo, the (previously marked) option will only track 3D points on photos that the point was marked on in previous epochs.
Motion Type 2 projects must use 3D tracking because there is no relationship between photos between epochs in type 2 projects.
The search for the target is started at the initial position. It can be done two ways: spiral contrast search, and NCC (Normalized Cross Correlation) . The spiral contrast search spirals out from the initial position looking for the first pixel transition that is biggest than a threshold. This method works well for high contrast targets with dark and low-noise backgrounds. The NCC method uses an image processing correlation method that is quite a bit slower but is also more robust. NCC works well with Template Targets and works well where there is a natural image or noisy background around the targets.
The marking can be done two ways: LSM (Least Squares Matching) and Centroid. See the Automatic Target Marking section for more information.
When a series of sub-pixel marked points are tracked, the Tracker determines which target type was used to initially mark the point. It then tracks these points into the selected epochs using the same template matching algorithm. For example, if epoch 1 had a number of Circular Targets and two types of Template Targets already marked, then when these points are tracked into epoch 2, the matching target type is used (that is after the search, the Circular Targets are sub-pixel marked with the Circular Target Marking Method, and the Template Targets are marked with the appropriate Target Template.