Note that the forward transformation of a PcdMap applies the distortion specified by this attribute and the inverse transformation removes this distortion. If the PcdMap is inverted (e.g. using astInvert), then the forward transformation will remove the distortion and the inverse transformation will apply it. The distortion itself will still be given by the same value of Disco.
Note, the value of this attribute may changed only if the PcdMap has no more than one reference. That is, an error is reported if the PcdMap has been cloned, either by including it within another object such as a CmpMap or FrameSet or by calling the astClone function.