Autodesk 00126-050008-1620A - Autocad 2006 Essentials User Manual page 63

WiseImage – User's Guide
Method
Linear conformal
Affine
Bilinear
Grid adaptive bilinear
Polynomial
Surface Splines
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
Linear
conformal
Affine
Bilinear
Grid the calibration grid must be
adaptive
bilinear
Polynomial
2nd degree
Polynomial
3rd degree
Polynomial
4th degree
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Distortion
For linear transformation - moving, rotating, and
proportional scaling.
For linear transformation - moving, rotating, and
non-proportional scaling. Raster ellipses can be
transformed to circles.
For parallelogram or trapezoid distortions on
map or mechanical drawings.
Useful for relatively small raster grid distortions
if the grid sells are convex.
Can only be used if the calibration grid is
defined.
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.
For distortions of all kinds, it is more accurate,
and works on an arbitrary set of pairs.
Number of
calibration pairs
required
2
3
4
defined.
6
10
15
Number of calibration
pairs producing non-
zero error
3
4
5
Non-Grid points are defined
7
11
16