The Sub-pixel Target Marker works with Circular Targets (both coded and non-coded targets) and Template Targets. See also Using Targets.
Circular Targets are solid circles or dots of contrasting color to the background (white dot on dark background for example). Coded Targets are circular targets with a code ring used for implicit referencing between photos. Template Targets are user defined shapes that can include shapes like crosses, grids, edges, corners, rectangles and even circles.
The Circular Target marker tends to be more consistent, more precise and faster than the Template Target marker so if you have a choice of target type, we recommend circles.
There are two methods of sub-pixel marker in PhotoModeler: the centroid method and the Least-Squares Matching (LSM) method. The centroid method is for circular targets only but works with any blob shape that is similar to a filled circle whereas the LSM method works with filled circles and Template Targets.
The target should be a consistent brightness and color and may be a light color on a dark background or a dark color on a light background. You can make your own physical targets with a laser printer or for an object with constant color you can use the removable sticky dots available at stationary stores.
Note: PhotoModeler only “sees” monochrome images when doing target marking (manual or automatic sub-pixel target marking). Color images are converted to monochrome / grayscale first before the sub-pixel algorithm is run. One has to be aware that targets that might look high contrast in a color image (dark yellow target on blue background for example) might not be high contrast when converted to grayscale. Color targets can be used with PhotoModeler as long as one ensure the “brightness” of the target differs considerably from the background.
The next sections deal primarily with Circular Targets. Circular Targets are the default in PhotoModeler and if no Template Targets are imported, then only Circular Targets will be marked manually or automatically. To find out more about how to load a Template Target and how to mark them, please see the Template Target Marking section.