This attribute is used when attempting to write a
FrameSet to a
FitsChan using a foreign encoding. It specifies the maximum departure from
linearity allowed on any axis within the mapping from pixel coordinates to
Intermediate World Coordinates. It is expressed in units of pixels. If an axis of the
Mapping is found to deviate from linearity by more than this amount, the write
operation fails. If the linearity test succeeds, a linear approximation to
the mapping is used to determine the FITS keyword values to be placed in the
FitsChan.
The default value is one tenth of a pixel.