Sip

class astropy.wcs.Sip(*a, b, ap, bp, crpix*)

Bases: object

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

Parameters

adouble 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.

bdouble 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.

apdouble 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.

bpdouble 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.

crpixdouble array[2]

The reference pixel.

Notes

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.

Attributes Summary

a	double array[a_order+1][a_order+1] Focal plane transformation matrix.
a_order	int (read-only) Order of the polynomial (A_ORDER).
ap	double array[ap_order+1][ap_order+1] Focal plane to pixel transformation matrix.
ap_order	int (read-only) Order of the polynomial (AP_ORDER).
b	double array[b_order+1][b_order+1] Pixel to focal plane transformation matrix.
b_order	int (read-only) Order of the polynomial (B_ORDER).
bp	double array[bp_order+1][bp_order+1] Focal plane to pixel transformation matrix.
bp_order	int (read-only) Order of the polynomial (BP_ORDER).
crpix	double array[naxis] Coordinate reference pixels (CRPIXja) for each pixel axis.

Methods Summary

foc2pix()	sip_foc2pix(foccrd, origin) -> double array[ncoord][nelem]
pix2foc()	sip_pix2foc(pixcrd, origin) -> double array[ncoord][nelem]

Attributes Documentation

a

double array[a_order+1][a_order+1] Focal plane transformation matrix.

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) Order of the polynomial (A_ORDER).

ap

double array[ap_order+1][ap_order+1] Focal plane to pixel transformation matrix.

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) Order of the polynomial (AP_ORDER).

b

double array[b_order+1][b_order+1] Pixel to focal plane transformation matrix.

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) Order of the polynomial (B_ORDER).

bp

double array[bp_order+1][bp_order+1] Focal plane to pixel transformation matrix.

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) Order of the polynomial (BP_ORDER).

crpix

double array[naxis] Coordinate reference pixels (CRPIXja) for each pixel axis.

Methods Documentation

foc2pix()

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

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

Parameters

foccrddouble array[ncoord][nelem]

Array of focal plane coordinates.

originint

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

pixcrddouble array[ncoord][nelem]

Returns an array of pixel coordinates.

Raises

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.

Parameters

pixcrddouble array[ncoord][nelem]

Array of pixel coordinates.

originint

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

foccrddouble array[ncoord][nelem]

Returns an array of focal plane coordinates.

Raises

MemoryError

Memory allocation failed.

ValueError

Invalid coordinate transformation parameters.