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.