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
ndarray
The
A_i_j
polynomial for pixel to focal plane transformation asdouble array[m+1][m+1]
. Its size must be (m + 1, m + 1) where m =A_ORDER
. b
ndarray
The
B_i_j
polynomial for pixel to focal plane transformation asdouble array[m+1][m+1]
. Its size must be (m + 1, m + 1) where m =B_ORDER
. ap
ndarray
The
AP_i_j
polynomial for pixel to focal plane transformation asdouble array[m+1][m+1]
. Its size must be (m + 1, m + 1) where m =AP_ORDER
. bp
ndarray
The
BP_i_j
polynomial for pixel to focal plane transformation asdouble array[m+1][m+1]
. Its size must be (m + 1, m + 1) where m =BP_ORDER
. crpix
ndarray
The reference pixel as
double array[2]
.
 a
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
sip_foc2pix(foccrd, origin) >
double array[ncoord][nelem]
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
 Returns
 pixcrd
ndarray
Returns an array of pixel coordinates as
double array[ncoord][nelem]
.
 pixcrd
 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
 Returns
 foccrd
ndarray
Returns an array of focal plane coordinates as
double array[ncoord][nelem]
.
 foccrd
 Raises
MemoryError
Memory allocation failed.
ValueError
Invalid coordinate transformation parameters.