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
double array[a_order+1][a_order+1]
Focal plane transformation matrix.int
(readonly) Order of the polynomial (A_ORDER
).double array[ap_order+1][ap_order+1]
Focal plane to pixel transformation matrix.int
(readonly) Order of the polynomial (AP_ORDER
).double array[b_order+1][b_order+1]
Pixel to focal plane transformation matrix.int
(readonly) Order of the polynomial (B_ORDER
).double array[bp_order+1][bp_order+1]
Focal plane to pixel transformation matrix.int
(readonly) Order of the polynomial (BP_ORDER
).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
(readonly) 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 newSip
object.

ap_order
¶ int
(readonly) 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 newSip
object.

b_order
¶ int
(readonly) 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 newSip
object.

bp_order
¶ int
(readonly) 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.