The chip size is the physical size of the charged coupled device (CCD) in a digital camera. Because images from digital cameras do not contain fiducial marks, the size of the CCDs is used to calculate the geometry of the camera. Most cameras have square sensor cells, but some, especially video cameras, can have rectangular sensor cells.
The y-scale factor is the ratio between the horizontal and the vertical size of each sensor cell in a digital camera. It is used when the CCD pixels are not square. By using the chip size and y-scale factor, the digital image is converted automatically to a normalized square-image coordinate system. The image can then be processed during the computation of the math model (the bundle adjustment) like an image acquired with a scanned-film camera.
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