1. A method of calibrating a barcode scanning tunnel, said method comprising: providing a scanning tunnel having a moveable surface, a camera having a sensor and optics that direct an image to the sensor from a field of view of the camera that includes the moveable surface, and a dimensioning device disposed with respect to the moveable surface so that the dimensioning device acquires dimensions of objects on the moveable surface passing through a field of view of the dimensioning device; estimating an orientation of the dimensioning device in the tunnel, wherein the orientation of the dimensioning device comprises a height of the dimensioning device above the moveable surface and a pitch of the dimensioning device about an axis parallel to an upper surface of the moveable surface; estimating an orientation of the camera in the tunnel, wherein the orientation of the camera comprises a height of the camera above the moveable surface and a pitch of the camera about an axis parallel to the upper surface of the moveable surface; disposing a first calibration object in the dimensioning device field of view and measuring an instance of a first dimension therein that relates to the calibration object and wherein the instance of the first dimension is dependent upon the orientation of the dimensioning device; disposing the first calibration object in the camera field of view and measuring an instance of a second dimension therein that corresponds to the first dimension and wherein the instance of the second dimension is dependent upon the orientation of the camera; based on the instance of the first dimension, the instance of the second dimension, the estimated orientation of the dimensioning device, and the estimated orientation of the camera, defining a relationship that relates an instance of the first dimension for an object on the moveable surface to control of a camera focal distance to the object on the moveable surface; disposing a second calibration object on the moveable surface and moving the second calibration object through the dimensioning device field of view and the camera field of view in a direction of travel of the moveable surface, wherein the dimensioning device field of view is upstream of the camera field of view with respect to the direction of travel, and wherein actual dimensions of one or more features of the second calibration object are predetermined; measuring, by the dimensioning device as the second calibration object moves through the dimensioning device field of view, an instance of the first dimension with respect to the second calibration object and an instance of a dimension of a first said feature of the second calibration object, wherein measurement of the instance of the dimension of the first feature corresponds to the orientation of the dimensioning device; controlling the focal distance in response to the instance of the first dimension measured at the measuring step, according to the relationship; after the controlling step, measuring, by the camera as the second calibration object moves through the camera field of view, an instance of a dimension of a second said feature of the second calibration object, wherein measurement of the instance of the dimension of the second feature corresponds to the orientation of the camera; revising an estimate of the orientation of the dimensioning device based on the instance of the dimension of the first feature; revising an estimate of the orientation of the camera based on the instance of the dimension of the second feature; and revising the relationship based on the revised estimate of the orientation of the dimensioning device and on the revised estimate of the orientation of the camera.