[AstroPy] Constructing Angle from a tuple specified as sign string plus numbers for degrees, arcmin, arcsec
embray at stsci.edu
Mon Aug 10 17:49:54 EDT 2015
On 08/10/2015 05:26 PM, Eric L. N. Jensen wrote:
> Hi all,
> I’m working with a table from CDS (i.e. from an ApJ paper) that specifies the declination coordinate in four separate columns: a string for the sign of the declination, and three numerical columns for degrees, arcminutes, and arcseconds. Is there a straightforward way to combine these into a single astropy.coordinates Angle object? The standard Angle function (constructor?) only accepts a tuple with three entries.
> I guess what I’m looking for is the inverse method of ‘signed_dms’.
> If it’s of use, the table I’m working with is here: http://iopscience.iop.org/0067-0049/184/1/18/fulltext/apjs300673t4_mrt.txt
> Thanks in advance for your help with this,
It seems a bit strange that the table format in this case indicates the sign of
the declination as a completely separate field, rather than as just part of the
numeric string. But I'm not intimately familiar with the quirks of the CDS
table format. Is that normal? I wonder if there's a way to get the CDS reader
to format those fields as a single column. Tom Aldcroft would know better.
You can instantiate an Angle array using a generator, so you could probably just
slurp in the data using a generator expression, allowing you to transform the
values one a time while creating the Angle rather than transforming the table
all at once first (please bear with the LISPiness of this example):
dec = Angle(((int(row + str(row)), row, row)
for row in table['DE-', 'DEd', 'DEm', 'DEs'))
# (Note: originally I used row[2:] above, but there seems to be an unrelated bug
involved in taking slices of rows...I'll report on that.)
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