Location of focal plane

A machine readable medium containing a computer program for generating a panoramic image of pan of a target, the computer program comprising instructions to cause a computer to:

• receive outputs from a scanner having a source of penetrating radiation facing a detector having an array of sensors far thc penetrating radiation, while the scanner scans a target positioned between the source of penetrating radiation and the detector with relative rotation of the scanner and the target so as to provide separate outputs representing radiation received at a plurality of sensor positions spaced apart in the circumferential direction of the relative rotation;
• generate a panoramic image by combining for each pixel of the panoramic image outputs from different sensor positions at different times during the relative rotation, the combined outputs being selected to represent rays of radiation passing through a point on a defined curve;
• display the generated panoramic image and a graphical representation of the defined curve;
• receive from a user instructions to alter the defined curve;
• and repeat the generating and displaying of the panoramic image using the altered curve.