2012

Affine Specifies arbitrary linear transformation in two dimensions consisting
of translation, independent X- and Y-scaling, rotation, and skewing with three
calibration points.
Use Affine when horizontal dimensions in a paper drawing are stretched with
respect to vertical dimensions, and lines that are supposed to be parallel
actually are parallel.
The RMS (root mean square) error reported after calibration measures how
close the program has come to making a perfect fit. Affine should be used if
the RMS is small.
Projective Specifies a transformation equivalent to a perspective projection
of one plane in space onto another plane with four calibration points. A
projective transformation provides a limited form of what cartographers call
rubber sheeting, in which different portions of the tablet surface are stretched
by varying amounts. Straight lines map into straight lines. Parallel lines do
not necessarily stay parallel.
Projective transformation corrects parallel lines that appear to converge.
Repeat Table Redisplays the computed table, which rates the transformation
types.
Transformation Table
Reports the number of calibration points and provides information about
each transformation type.
Outcome of Fit
Reports the outcome of fit for each of the transformation types. If the outcome
of fit is not Success or Exact for any of the transformation types, the program
reports failure of the entire calibration process and ends the command. The
remaining entries in each column are blank unless Outcome of Fit is Success.
Exact Indicates the correct number of points for a valid transformation.
Success Indicates more than enough points. The program succeeded in fitting
a transformation to the data.
Impossible Indicates not enough points.
Failure Indicates enough points, but the program was unable to fit a
transformation to the points, usually because some points were colinear or
coincident.
Canceled Indicates that the fit process was canceled. This outcome occurs
only with the projective transformation.
1914 | Chapter 20 T Commands