Set Coordinate System Concepts

The Set Coordinate System step defines a coordinate system relative to a feature in the image.

In a typical machine vision inspection, you limit your inspection and processing to a region of interest rather than the entire image. To limit the inspection area, the parts of the object you are interested in must always appear inside the region of interest you define.

If the object under inspection is always at the same location and orientation in the images you need to process, defining a region of interest is simple. However, the object under inspection often appears shifted or rotated within the images you need to process. When this occurs, the region of interest needs to shift and rotate with the parts of the object you are interested in. In order for the region of interest to move in relation to the object, you need to define a coordinate system relative to a feature in the image.

A coordinate system is specified by its origin and the angle its x-axis makes with the horizontal axis of the image. Assign a coordinate system based on how you expect the object to move in the image. If the object is going to only translate in the horizontal or vertical directions, you need only to select a feature whose location can represent the origin of the coordinate system. The angle is 0 by default. If the object is going to translate and rotate, you need to select features that can represent the location of the origin and angle of the coordinate system.