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Sip

class pywcs.Sip

The Sip class performs polynomial distortion correction using the SIP convention in both directions.

Shupe, D. L., M. Moshir, J. Li, D. Makovoz and R. Narron. 2005. “The SIP Convention for Representing Distortion in FITS Image Headers.” ADASS XIV.
  • a: double array[m+1][m+1]. The A_i_j polynomial for pixel to focal plane transformation. Its size must be (m + 1, m + 1) where m = A_ORDER.
  • b: double array[m+1][m+1]. The B_i_j polynomial for pixel to focal plane transformation. Its size must be (m + 1, m + 1) where m = B_ORDER.
  • ap: double array[m+1][m+1]. The AP_i_j polynomial for pixel to focal plane transformation. Its size must be (m + 1, m + 1) where m = AP_ORDER.
  • bp: double array[m+1][m+1]. The BP_i_j polynomial for pixel to focal plane transformation. Its size must be (m + 1, m + 1) where m = BP_ORDER.
  • crpix: double array[2]. The reference pixel.
foc2pix()

sip_foc2pix(foccrd, origin) -> double array[ncoord][nelem]

Convert focal plane coordinates to pixel coordinates using the SIP polynomial distortion convention.

  • foccrd: double array[ncoord][nelem]. Array of focal plane coordinates.
  • origin: int. Specifies the origin of pixel values. The Fortran and FITS standards use an origin of 1. Numpy and C use array indexing with origin at 0.

Returns an array of pixel coordinates.

Exceptions:

  • MemoryError: Memory allocation failed.
  • ValueError: Invalid coordinate transformation parameters.
pix2foc()

sip_pix2foc(pixcrd, origin) -> double array[ncoord][nelem]

Convert pixel coordinates to focal plane coordinates using the SIP polynomial distortion convention.

  • pixcrd: double array[ncoord][nelem]. Array of pixel coordinates.
  • origin: int. Specifies the origin of pixel values. The Fortran and FITS standards use an origin of 1. Numpy and C use array indexing with origin at 0.

Returns an array of focal plane coordinates.

Exceptions:

  • MemoryError: Memory allocation failed.
  • ValueError: Invalid coordinate transformation parameters.
a

double array[a_order+1][a_order+1]

The SIP A_i_j matrix used for pixel to focal plane transformation.

Its values may be changed in place, but it may not be resized, without creating a new Sip object.

a_order

int (read-only)

The order of the polynomial in the SIP A_i_j array (A_ORDER).

ap

double array[ap_order+1][ap_order+1]

The SIP AP_i_j matrix used for focal plane to pixel transformation. Its values may be changed in place, but it may not be resized, without creating a new Sip object.

ap_order

int (read-only)

The order of the polynomial in the SIP AP_i_j array (AP_ORDER). list of strings[naxis]

List of CTYPEia keyvalues.

The ctype keyword values must be in upper case and there must be zero or one pair of matched celestial axis types, and zero or one spectral axis.

b

double array[b_order+1][b_order+1]

The SIP B_i_j matrix used for pixel to focal plane transformation. Its values may be changed in place, but it may not be resized, without creating a new Sip object.

b_order

int (read-only)

The order of the polynomial in the SIP B_i_j array (B_ORDER).

bp

double array[bp_order+1][bp_order+1]

The SIP BP_i_j matrix used for focal plane to pixel transformation. Its values may be changed in place, but it may not be resized, without creating a new Sip object.

bp_order

int (read-only)

The order of the polynomial in the SIP BP_i_j array (BP_ORDER). int (read-only)

EXTLEV identifying the binary table extension.

crpix

double array[naxis]

Coordinate reference pixels (CRPIXja) for each pixel axis.