CCDData¶
-
class
astropy.nddata.
CCDData
(*args, **kwd)[source]¶ Bases:
astropy.nddata.NDDataArray
A class describing basic CCD data.
The CCDData class is based on the NDData object and includes a data array, uncertainty frame, mask frame, flag frame, meta data, units, and WCS information for a single CCD image.
- Parameters
- data
CCDData
-like ornumpy.ndarray
-like The actual data contained in this
CCDData
object. Note that the data will always be saved by reference, so you should make a copy of thedata
before passing it in if that’s the desired behavior.- uncertainty
StdDevUncertainty
,VarianceUncertainty
,InverseVariance
,numpy.ndarray
or None, optional Uncertainties on the data. If the uncertainty is a
numpy.ndarray
, it it assumed to be, and stored as, aStdDevUncertainty
. Default isNone
.- mask
numpy.ndarray
or None, optional Mask for the data, given as a boolean Numpy array with a shape matching that of the data. The values must be
False
where the data is valid andTrue
when it is not (like Numpy masked arrays). Ifdata
is a numpy masked array, providingmask
here will causes the mask from the masked array to be ignored. Default isNone
.- flags
numpy.ndarray
orFlagCollection
or None, optional Flags giving information about each pixel. These can be specified either as a Numpy array of any type with a shape matching that of the data, or as a
FlagCollection
instance which has a shape matching that of the data. Default isNone
.- wcs
WCS
or None, optional WCS-object containing the world coordinate system for the data. Default is
None
.- metadict-like object or None, optional
Metadata for this object. “Metadata” here means all information that is included with this object but not part of any other attribute of this particular object, e.g. creation date, unique identifier, simulation parameters, exposure time, telescope name, etc.
- unit
Unit
or str, optional The units of the data. Default is
None
.Warning
If the unit is
None
or not otherwise specified it will raise aValueError
- data
- Raises
- ValueError
If the
uncertainty
ormask
inputs cannot be broadcast (e.g., match shape) ontodata
.
Notes
CCDData
objects can be easily converted to a regularNumpy array using
numpy.asarray
.
For example:
>>> from astropy.nddata import CCDData >>> import numpy as np >>> x = CCDData([1,2,3], unit='adu') >>> np.asarray(x) array([1, 2, 3])
This is useful, for example, when plotting a 2D image using matplotlib.
>>> from astropy.nddata import CCDData >>> from matplotlib import pyplot as plt >>> x = CCDData([[1,2,3], [4,5,6]], unit='adu') >>> plt.imshow(x)
- Attributes
- known_invalid_fits_unit_strings
A dictionary that maps commonly-used fits unit name strings that are technically invalid to the correct valid unit type (or unit string). This is primarily for variant names like “ELECTRONS/S” which are not formally valid, but are unambiguous and frequently enough encountered that it is convenient to map them to the correct unit.
Methods
read(*args, **kwargs)
Classmethod
to create an CCDData instance based on aFITS
file. This method usesfits_ccddata_reader()
with the provided parameters.write(*args, **kwargs)
Writes the contents of the CCDData instance into a new
FITS
file. This method usesfits_ccddata_writer()
with the provided parameters.Attributes Summary
ndarray
-like : The stored dataset.any type : Uncertainty in the dataset, if any.
Unit
: Unit for the dataset, if any.any type : A world coordinate system (WCS) for the dataset, if any.
Methods Summary
add
(operand[, operand2])copy
(self)Return a copy of the CCDData object.
divide
(operand[, operand2])multiply
(operand[, operand2])subtract
(operand[, operand2])to_hdu
(self[, hdu_mask, hdu_uncertainty, …])Creates an HDUList object from a CCDData object.
Attributes Documentation
-
header
¶
-
known_invalid_fits_unit_strings
= {'ELECTRONS': Unit("electron"), 'ELECTRONS/S': Unit("electron / s"), 'electrons': Unit("electron")}¶
-
uncertainty
¶ any type : Uncertainty in the dataset, if any.
Should have an attribute
uncertainty_type
that defines what kind of uncertainty is stored, such as'std'
for standard deviation or'var'
for variance. A metaclass defining such an interface isNDUncertainty
but isn’t mandatory.
-
wcs
¶ any type : A world coordinate system (WCS) for the dataset, if any.
Methods Documentation
-
classmethod
add
(operand, operand2=None, **kwargs)¶
-
classmethod
divide
(operand, operand2=None, **kwargs)¶
-
classmethod
multiply
(operand, operand2=None, **kwargs)¶
-
classmethod
subtract
(operand, operand2=None, **kwargs)¶
-
to_hdu
(self, hdu_mask='MASK', hdu_uncertainty='UNCERT', hdu_flags=None, wcs_relax=True, key_uncertainty_type='UTYPE')[source]¶ Creates an HDUList object from a CCDData object.
- Parameters
- hdu_mask, hdu_uncertainty, hdu_flagsstr or None, optional
If it is a string append this attribute to the HDUList as
ImageHDU
with the string as extension name. Flags are not supported at this time. IfNone
this attribute is not appended. Default is'MASK'
for mask,'UNCERT'
for uncertainty andNone
for flags.- wcs_relaxbool
Value of the
relax
parameter to use in converting the WCS to a FITS header usingto_header
. The commonCTYPE
RA---TAN-SIP
andDEC--TAN-SIP
requiresrelax=True
for the-SIP
part of theCTYPE
to be preserved.- key_uncertainty_typestr, optional
The header key name for the class name of the uncertainty (if any) that is used to store the uncertainty type in the uncertainty hdu. Default is
UTYPE
.New in version 3.1.
- Returns
- hdulist
HDUList
- hdulist
- Raises
- ValueError
If
self.mask
is set but not anumpy.ndarray
.If
self.uncertainty
is set but not a astropy uncertainty type.If
self.uncertainty
is set but has another unit thenself.data
.
- NotImplementedError
Saving flags is not supported.