title: Linearity of cephalometric digitizers.
abstract: The present study aimed to develop a test procedure to diagnose and visualize errors in linearity of digitizing tablets. Errors of linearity are caused by the distortion of the x- and y-co-ordinates of the digitizing tablet. This results in a given object apparently having different dimensions when recorded on different locations of the digitizing surface. The test is performed by systematic recording of n equally spaced points from a calibrated test foil. Algorithms were developed to calculate the difference matrices DXji and DYji between expected and observed values of the co-ordinates. Three-dimensional mapping of the non-linearity of the x- and y-co-ordinates was performed by the UNIRAS-geopak, a 3-D surface representative system. The tested digitizers showed varying degrees of scaling errors, fields of non-linearity, and random noise. Most digitizers allow for correction of scaling by setting of switches in the control unit. A method is suggested for correction of non-linearities by use of the DXji and DYji matrices in the digitizing programme.
authors.affiliation: Department of Orthodontics, Royal Dental College, Copenhagen, Denmark.
authors.forename: E
authors.initials: E
authors.lastname: Eriksen
authors.forename: B
authors.initials: B
authors.lastname: Solow
mesh_terms: D000465:Algorithms; D002138:Calibration; D002508:Cephalometry / Q000295:instrumentation*; D003626:Data Display; D006801:Humans; D011856:Radiographic Image Enhancement / Q000295:instrumentation*; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D012984:Software; D013223:Statistics as Topic