# Nonlinear Calibration

The Checkerboard Calibration tool is one of two calibration tools provided by VisionPro.

The tool works in either linear or nonlinear (with warping) mode. Both modes create a mathematical mapping between physical coordinates and the pixels of a given input image. In nonlinear mode, the tool measures, and then corrects, perspective and radial distortions.

When you use the N-point calibration tool or the Checkerboard calibration tool in linear mode to calibrate an image, the resulting calibration can only account for aspect ratio distortion (as well as any translation or rotation).

Note: The Checkerboard calibration tool supports the use of both checkerboard and grid-of-dots calibration plates. While either type of plate can be used to perform nonlinear calibration, using a checkerboard plate will produce a more accurate calibration than a grid-of-dots plate, particularly when nonlinear distortion is present. All of the examples, illustrations, and discussions in this topic show the use of a checkerboard calibration plate.