REGISTER solves for the coefficients of a linear plate transformation given the positions of at least 3 stars appearing in all the frames concerned. The plate transformation is of the form:
X(REF) = X(PLATE) + AX*X(PLATE) + BX*Y(PLATE) + CX Y(REF) = Y(PLATE) + AY*X(PLATE) + BY*Y(PLATE) + CYThe reference frame is taken to be the first frames specified, but shifted in rows and columns so that the positions of the reference stars average to 0; if the NOMEAN keyword is used, then the first frame will be the reference frame, with no shift at all ( this should be the default, but isn't for historical reasons - this may change someday ...)
If the HEADER option is specified, the stellar positions are read from the image header in cards(RSTARX1,RSTARY1),(RSTARX2,RSTARY2), (RSTARX3,RSTARY3) ... up to a maximum of 9 stars. These cards can be placed in the header using the MARKSTAR command specifying a buffer number and the keyword REF. If the HEADER option is not used, the program will prompt for two files containing the stellar positions in each of two frames. In this case, only 2 frames can be done at a time.
If the LOAD keyword is specified, then the coefficients of the fits are loaded into each header in the cards REF_AX, REF_BX, REF_CX, REF_AY, REF_BY, and REF_CY.