# Calibration Coordinate Spaces

The calculation of the best-fit, 2D calibrated transform involves three coordinate spaces:

Coordinate Space | Description
--- | ---
Uncalibrated | Uncalibrated space is the selected space of the input image before running your calibration tool. It is almost always the pixel-based root ("@") space of an acquired image.
Raw calibrated | Raw calibrated space is a calibrated, unadjusted space defined by fitting the physical locations of the raw calibrated points to the uncalibrated points. This space determines the units of the computed calibration transform. It differs from the final calibrated space only in the placement of the origin, which can be rigidly adjusted.
Calibrated | The calibrated space is the desired physical coordinate space. It is typically expressed in real-world units, like inches or microns, and aligned with some well-known feature in the physical world. The calibrated space represents the result of the calibration computation. The calibrated space takes into account any rigid adjustment (translation and rotation) you supply.

Note: The selected space of the calibration image is, by definition, always the uncalibrated space. This is usually the root ("@") space. The selected space of the run-time images must be the same selected space or have the same relationship to the physical world. In practice, this means that you must acquire all calibration and run-time images through the same camera and lens. The camera and lens must also retain their original set-up or calibration time settings. For example, changing the acquisition format (in resolution), moving the camera, or adjusting the focus of the lens will invalidate the computed 2D transformation that maps pixel to real-world coordinates.