polynomial distortions in WCS

Emmanuel Bertin's excellent package SCAMP for WCS refinement uses a proposed WCS polynomial distortion standard you might call PV; astrometry.net uses SIP, which is published here (PDF), though it remains a pseudo-standard. Because astrometry.net and SCAMP made different decisions, I spent an unreasonable amount of time today trying to understand the PV pseudo-standard and whether or how we can translate. The difficulty of this was enhanced by the fact that all of the PV sections of the relevant papers were removed prior to publication.


  1. What happened to the other zero-th order terms for the third-order polynomial after equation 3? Should f(u,v) be:
    f(u,v)=A_0_0 + A_1_0u + A_0_1v + A_2_9u^2......

  2. Dear David,
    Reviving this post after some years :-)
    Did you manage to find the transformation between scamp PV and TAN-SIP ?
    If so, do you have a tool to convert a .head produced by scamp into a TAN-SIP header and vice-versa?

  3. @Jerbé: I am not sure we ever did. Send email to Lang to ask. I think maybe Bertin himself did it at some point, because I think SCAMP may now take SIP?