I need to understand the data PinPoint has added to the image FITS headers and above all the distortion coefficients (TR1_0, TR1_1, ... TR1_14, TR2_0, ... TR2_14). I can make an educated guess of what they might mean, but I truly need to know - guessing is not an acceptable option. Reference Guide (a companion to ACP Observatory Control Software) states: "These terms are described in more detail in the document called FITS World Coordinate Systems (WCS).". I have spent several days going through all the material and scientific articles within that NASA web site and I have never ever seen any reference to TR1 and TR2 coefficients. I may just be blind, or they are not there.

Any suggestions on where to find the polynomial those coefficients describe?

I promise to be tremendously grateful for the answer,
// Rami Rekola