[AstroPy] pywcs problem
Stefan Schwarzburg
stefan.schwarzburg at googlemail.com
Thu Jul 3 10:51:59 EDT 2008
Hi,
I have a problem with pywcs. I tried to get a feeling for the library by
playing around with it.
At the end of the email, there is my modified "test", which is taken from
here "http://stsdas.stsci.edu/astrolib/pywcs-1.0a1-4.3_api/"
Now when I let this test run, I get the following output:
>-------------------USING TEST HEADER-------------------
>
>
>
>
>
>
>
>
>
>[[ 99.322 36.3123]]
To me this seems rather strange, since in the testheader, there is this part
here:
CRPIX1 = 151.0 / Reference pixel on axis 1
CRPIX2 = 151.0 / Reference pixel on axis 2
CRVAL1 = 279.322 / Value at ref. pixel on axis 1
CRVAL2 = -7.3123 / Value at ref. pixel on axis 2
and my test uses [150,150] as test pixel position.
Should I not get something like:~ [[279, -7]] ?
I hope someone can help me here.
Thanks,
Stefan
#!/usr/bin/env python
import numpy
import pywcs
import pyfits
import sys
print "-------------------USING TEST HEADER-------------------"
h = """
SIMPLE = T / file does conform to FITS standard
BITPIX = -32 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 301 / length of data axis 1
NAXIS2 = 301 / length of data axis 2
EXTEND = T / FITS dataset may contain extensions
COMMENT FITS (Flexible Image Transport System) format is defined in
'Astronomy
COMMENT and Astrophysics', volume 376, page 359; bibcode:
2001A&A...376..359H
CTYPE1 = 'RA---CAR' / Type of co-ordinate on axis 1
CTYPE2 = 'DEC--CAR' / Type of co-ordinate on axis 2
CRPIX1 = 151.0 / Reference pixel on axis 1
CRPIX2 = 151.0 / Reference pixel on axis 2
CRVAL1 = 279.322 / Value at ref. pixel on axis 1
CRVAL2 = -7.3123 / Value at ref. pixel on axis 2
CDELT1 = -0.02 / Pixel size on axis 1
CDELT2 = 0.02 / Pixel size on axis 2
MJD-OBS = 51544.4992571308 / Modified Julian Date of observation
DATE-OBS= '2000-01-01T11:58:55.816'/ Date of observation
RADESYS = 'FK5 ' / Reference frame for RA/DEC values
EQUINOX = 2000.0 / [yr] Epoch of reference equinox
OBJECT = 'SOMETHING'
BUNIT = 'Count '
BSCALE = 1.0
BZERO = 0.0
"""
wcs = pywcs.WCS(h)
# Print out the "name" of the WCS, as defined in the FITS header
print wcs.name
# Some interesting pixel coordinates
pixcrd = numpy.array([[150,150]], numpy.double)
# Convert pixel coordinates to world coordinates
world = wcs.pixel2world(pixcrd)
print world
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