1. In a computer system, a method comprising: receiving images of a calibration object whose geometry is one-dimension in space, the received images showing the calibration object in several distinct positions, wherein: the calibration object comprises three or more collinear points with known relative positions between the points; and at least one of the collinear points remains fixed with respect to the other points in the received images showing the calibration object in several distinct position; and calculating a calibration for a camera based on the received images of the calibration object.