1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
|
# Copyright (c) 2016 Weitian LI <liweitianux@live.com>
# MIT license
"""
FITS utilities.
"""
from datetime import datetime, timezone
import numpy as np
from astropy.io import fits
import healpy as hp
# Reference:
# http://docs.astropy.org/en/stable/io/fits/usage/table.html#column-creation
FITS_COLUMN_FORMATS = {
np.dtype("bool"): "L",
np.dtype("uint8"): "B",
np.dtype("int16"): "I",
np.dtype("int32"): "J",
np.dtype("int64"): "K",
np.dtype("float32"): "E",
np.dtype("float64"): "D",
np.dtype("complex64"): "C",
np.dtype("complex128"): "M",
}
def read_fits_healpix(filename):
"""Read the HEALPix map from a FITS file or a HDU to 1D array
in *RING* ordering.
Parameters
----------
filename : str or `~astropy.io.fits.BinTableHDU`
Filename of the HEALPix FITS file,
or an `~astropy.io.fits.BinTableHDU` instance.
Returns
-------
data : 1D `~numpy.ndarray`
HEALPix data in *RING* ordering
header : `~astropy.io.fits.Header`
Header of the input FITS file
NOTE
----
This function wraps on `healpy.read_map()`, but set the data type of
data array to its original value as in FITS file, as well as return
FITS header as `~astropy.io.fits.Header` instance.
"""
if isinstance(filename, fits.BinTableHDU):
hdu = filename
else:
hdu = fits.open(filename)[0]
dtype = hdu.data.dtype
header = hdu.header
data = hp.read_map(hdu, nest=False, verbose=False)
return (data.astype(dtype), header)
def write_fits_healpix(filename, hpmap, header=None, clobber=False):
"""Write the HEALPix map to a FITS file with proper header as well
as the user-provided header.
This function currently only support one style of HEALPix with the
following specification:
- Only one column: I (intensity)
- ORDERING: RING
- COORDSYS: G (Galactic)
- OBJECT: FULLSKY
- INDXSCHM: IMPLICIT
Parameters
----------
filename : str
Filename of the output file to write the HEALPix map data
hpmap : numpy.ndarray (1D)
1D array containing the HEALPix map data, and the ordering
scheme should be "RING";
The data type is preserved in the output FITS file.
header : fits.Header object
Extra header to be written
clobber : bool
Whether to overwrite the existing file?
NOTE
----
- This function is intended to replace the most common case of
`healpy.write_map()`, which still uses some deprecated functions of
`numpy` and `astropy`, meanwhile, it interface/arguments is not very
handy.
- This function (currently) only implement the very basic feature of
the `healpy.write_map()`.
"""
hpmap = np.array(hpmap)
if hpmap.ndim != 1:
raise ValueError("Invalid HEALPix data: only support 1D array")
#
npix = hpmap.size
nside = int((npix / 12) ** 0.5)
colfmt = FITS_COLUMN_FORMATS.get(hpmap.dtype)
if hpmap.size > 1024:
hpmap = hpmap.reshape(int(hpmap.size/1024), 1024)
colfmt = "1024" + colfmt
#
hdr = fits.Header()
# set HEALPix parameters
hdr["PIXTYPE"] = ("HEALPIX", "HEALPix pixelization")
hdr["ORDERING"] = ("RING",
"Pixel ordering scheme, either RING or NESTED")
hdr["COORDSYS"] = ("G", "Ecliptic, Galactic or Celestial (equatorial)")
hdr["NSIDE"] = (nside, "HEALPix resolution parameter")
hdr["NPIX"] = (npix, "Total number of pixels")
hdr["FIRSTPIX"] = (0, "First pixel # (0 based)")
hdr["LASTPIX"] = (npix-1, "Last pixel # (0 based)")
hdr["INDXSCHM"] = ("IMPLICIT", "Indexing: IMPLICIT or EXPLICIT")
hdr["OBJECT"] = ("FULLSKY", "Sky coverage, either FULLSKY or PARTIAL")
#
hdr["EXTNAME"] = ("HEALPIX", "Name of the binary table extension")
hdr["CREATOR"] = (__name__, "File creator")
hdr["DATE"] = (
datetime.now(timezone.utc).astimezone().isoformat(),
"File creation date"
)
# merge user-provided header
if header is not None:
hdr.update(fits.Header(header))
#
hdu = fits.BinTableHDU.from_columns([
fits.Column(name="I", array=hpmap, format=colfmt)
], header=hdr)
hdu.writeto(filename, clobber=clobber, checksum=True)
|
