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:  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.
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 transformationa_order
int
(readonly) Order of the polynomial (A_ORDER
).ap
double array[ap_order+1][ap_order+1]
Focal plane to pixelap_order
int
(readonly) Order of the polynomial (AP_ORDER
).b
double array[b_order+1][b_order+1]
Pixel to focal planeb_order
int
(readonly) Order of the polynomial (B_ORDER
).bp
double array[bp_order+1][bp_order+1]
Focal plane to pixelbp_order
int
(readonly) Order of the polynomial (BP_ORDER
).crpix
double array[naxis]
Coordinate reference pixels (CRPIXja
) forMethods 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:  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:  pixcrd : double 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:  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:  foccrd : double array[ncoord][nelem]
Returns an array of focal plane coordinates.
Raises:  MemoryError
Memory allocation failed.
 ValueError
Invalid coordinate transformation parameters.