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Documentation about odd vs. even cutout size in asdf_cut #128

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Sep 23, 2024
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Documentation about odd vs. even cutout size in asdf_cut #128

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Documentation about odd vs even cutout size in asdf_cut, change defau…
snbianco Sep 20, 2024
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snbianco Sep 20, 2024
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9 changes: 5 additions & 4 deletions astrocut/asdf_cutouts.py
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Original file line number Diff line number Diff line change
Expand Up @@ -257,16 +257,14 @@ def _write_asdf(cutout: astropy.nddata.Cutout2D, gwcsobj: gwcs.wcs.WCS, outfile:
af.write_to(outfile)


def asdf_cut(input_file: Union[str, pathlib.Path, S3Path], ra: float, dec: float, cutout_size: int = 20,
def asdf_cut(input_file: Union[str, pathlib.Path, S3Path], ra: float, dec: float, cutout_size: int = 25,
output_file: Union[str, pathlib.Path] = "example_roman_cutout.fits",
write_file: bool = True, fill_value: Union[int, float] = np.nan, key: str = None,
secret: str = None, token: str = None, verbose: bool = False) -> astropy.nddata.Cutout2D:
"""
Takes a single ASDF input file (`input_file`) and generates a cutout of designated size `cutout_size`
around the given coordinates (`coordinates`).

Preliminary proof-of-concept functionality.

Parameters
----------
input_file : str | Path | S3Path
Expand All @@ -276,7 +274,10 @@ def asdf_cut(input_file: Union[str, pathlib.Path, S3Path], ra: float, dec: float
dec : float
The declination of the central cutout.
cutout_size : int
Optional, default 20. The image cutout pixel size.
Optional, default 25. The image cutout pixel size.
Note: Odd values for `cutout_size` generally result in a cutout that is more accurately
centered on the target coordinates compared to even values, due to the symmetry of the
pixel grid.
output_file : str | Path
Optional, default "example_roman_cutout.fits". The name of the output cutout file.
write_file : bool
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19 changes: 12 additions & 7 deletions docs/astrocut/index.rst
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Expand Up @@ -365,8 +365,8 @@ The Nancy Grace Roman Space Telescope will store its data using the Advanced Sci
Creating ASDF Cutouts
----------------------

The function `asdf_cut` performs a cutout of an ASDF file and returns the result as either a FITS file or an ASDF file.
The format of the cutout is determined by the filename extension of the `output_file` parameter. In the below example, a cutout is written as a FITS file.
The function `~astrocut.asdf_cut` performs a cutout of an ASDF file and returns the result as either a FITS file or an ASDF file.
The format of the cutout is determined by the filename extension of the ``output_file`` parameter. In the below example, a cutout is written as a FITS file.
The cutout FITS file format is described `here <file_formats.html#fits-cutout-files>`__.

.. code-block:: python
Expand All @@ -379,16 +379,21 @@ The cutout FITS file format is described `here <file_formats.html#fits-cutout-fi

>>> center_coord = SkyCoord("80.15189743 29.74561219", unit='deg')

>>> cutout_file = asdf_cut(input_file, center_coord.ra, center_coord.dec, cutout_size=200,
>>> cutout_file = asdf_cut(input_file, center_coord.ra, center_coord.dec, cutout_size=205,
... output_file="roman-demo.fits") #doctest: +SKIP

>>> cutout_hdulist = fits.open(cutout_file) #doctest: +SKIP
>>> cutout_hdulist.info() #doctest: +SKIP
Filename: roman-demo.fits
No. Name Ver Type Cards Dimensions Format
0 PRIMARY 1 PrimaryHDU 25 (200, 200) float32
0 PRIMARY 1 PrimaryHDU 25 (205, 205) float32

`asdf_cut` accepts S3 URIs to perform cutouts on ASDF files from the cloud.
.. warning::
Due to the symmetry of the pixel grid, odd values for ``cutout_size`` generally produce
cutouts that are more accurately centered on the target coordinates than even values
for ``cutout_size``.

`~astrocut.asdf_cut` also accepts S3 URIs to perform cutouts on ASDF files from the cloud.
In this example, a cutout is performed on a cloud file and written as an ASDF file. The cutout ASDF file format is described `here <file_formats.html#asdf-cutout-files>`__.

.. code-block:: python
Expand All @@ -400,10 +405,10 @@ In this example, a cutout is performed on a cloud file and written as an ASDF fi

>>> center_coord = SkyCoord("80.15189743 29.74561219", unit='deg')

>>> cutout_file = asdf_cut(s3_uri, center_coord.ra, center_coord.dec, cutout_size=200,
>>> cutout_file = asdf_cut(s3_uri, center_coord.ra, center_coord.dec, cutout_size=205,
... output_file="roman-demo.asdf") #doctest: +SKIP

When requesting a cutout that is partially outside of image bounds, the `fill_value` parameter is used to preserve the cutout shape and fill outside pixels.
When requesting a cutout that is partially outside of image bounds, the ``fill_value`` parameter is used to preserve the cutout shape and fill outside pixels.



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