Autodesk 05726-091452-9060 User Guide - Page 63

WiseImage - User's Guide Method Distortion Linear conformal For linear transformation - moving, rotating, and proportional scaling. Affine For linear transformation - moving, rotating, and non-proportional scaling. Raster ellipses can be transformed to circles. Bilinear For parallelogram or trapezoid distortions on map or mechanical drawings. Grid adaptive bilinear Useful for relatively small raster grid distortions if the grid sells are convex. Can only be used if the calibration grid is defined. Polynomial Nonlinear deformations caused by either three- dimensional expansion of the original graphic document or by an image type itself. For example, aerial photos of the Earth's surface. Surface Splines For distortions of all kinds, it is more accurate, and works on an arbitrary set of pairs. For every calibration method there is a minimum number of calibration pairs that enables the use of this model. If the number of calibration pairs exceeds a certain value, then all models, except Surface Splines, produce a non-zero deviation. The following table describes the restrictions on the number of calibration pairs for each calibration method. Method name Number of calibration pairs required Number of calibration pairs producing non- zero error Linear conformal Affine Bilinear Grid adaptive bilinear Polynomial 2nd degree Polynomial 3rd degree Polynomial 4th degree 2 3 4 the calibration grid must be defined. 6 10 15 3 4 5 Non-Grid points are defined 7 11 16 64