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# Copyright (c) 2017 Weitian LI <weitian@aaronly.me>
# MIT license
"""
Create WCS for sky projection.
"""
import numpy as np
from astropy.wcs import WCS
from .units import UnitConversions as AUC
def make_wcs(center, size, pixelsize, frame="ICRS", projection="TAN"):
"""
Make WCS for sky projection usages, etc.
Parameters
----------
center : (xcenter, ycenter) float tuple
The equatorial/galactic coordinate of the sky/image center.
Unit: [deg]
size : (xsize, ysize) int tuple
The size (width, height) of the sky/image.
pixelsize : float
The pixel size of the sky/image.
Unit: [arcsec]
frame : str, "ICRS" or "Galactic"
The coordinate frame, only one of ``ICRS`` or ``Galactic``.
projection : str, "TAN" or "CAR"
The projection algorithm used by the sky/image, currently only
support ``TAN`` (tangential), ``CAR`` (Cartesian).
Returns
-------
w : `~astropy.wcs.WCS`
Created WCS header/object
TODO/XXX
---------
To support other projections, e.g., ``SIN`` (common in radio astronomy).
"""
xcenter, ycenter = center # [ deg ]
xsize, ysize = size
delt = pixelsize * AUC.arcsec2deg # [ deg ]
if projection.upper() not in ["TAN", "CAR"]:
raise ValueError("unsupported projection: " % projection)
if frame.upper() == "ICRS":
ctype = ["RA---" + projection.upper(), "DEC--" + projection.upper()]
elif frame.upper() == "GALACTIC":
ctype = ["GLON-" + projection.upper(), "GLAT-" + projection.upper()]
else:
raise ValueError("unknown frame: " % frame)
w = WCS(naxis=2)
w.wcs.ctype = ctype
w.wcs.crval = np.array([xcenter, ycenter])
w.wcs.crpix = np.array([xsize/2.0-0.5, ysize/2.0-0.5])
w.wcs.cdelt = np.array([-delt, delt])
w.wcs.cunit = ["deg", "deg"]
w.wcs.equinox = 2000.0
return w
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