[AstroPy] (no subject)
Dave Lane
dlane at ap.stmarys.ca
Fri Jan 15 12:53:07 EST 2016
Hi,
I'm having trouble with 'wcs_world2pix' giving the wrong answers for
pixel positions (off by about 10 pixels) compared to other software
include including that interpreted by ds9 image display. The optical
images were plate-solved by pinpoint (from dc3 dreams). I am getting the
error:
WARNING: FITSFixedWarning: RADECSYS= 'FK5 ' / Equatorial coordinate
system
RADECSYS is non-standard, use RADESYSa. [astropy.wcs.wcs]
Any suggestions on how to proceed?
--- Dave
--->>>
A code snipped is as follows:
import astropy.io.fits
from astropy import wcs
import numpy as np
from phot import aperphot,hms,dms
imagelist=["/home/bgo/bgoimages/2015-11-09/observations/processed/VXCYG-102453-V.fit"]
RAtarget=hms("20:57:20.8")
DECtarget=dms("+40:10:39")
imagefile=imagelist[1] # path to the image
hdulist = astropy.io.fits.open(imagefile)
w = wcs.WCS(hdulist['PRIMARY'].header)
world = np.array([[RAtarget, DECtarget]])
pix = w.wcs_world2pix(world,1)
print "Pixel Coordinates: ", pix[0,0], pix[0,1]
radec = w.wcs_pix2world(pix,1)
print "RADEC Coordinates: ", radec[0,0], radec[0,1]
observation=aperphot(imagefile, timekey=None, pos=[pix[0,0], pix[0,1]],
dap=[10,15,20], resamp=2,retfull=False)
print "Aperture flux:", observation.phot
print "Background: ", observation.bg
The pertinent header keys are:
RADECSYS= 'FK5 ' / Equatorial coordinate system
RA = '20 57 22.20' / [hms J2000] Target right ascension
DEC = '+40 19 11.0' / [dms +N J2000] Target declination
EQUINOX = 2000.0 / Equatorial coordinates are J2000
EPOCH = 2000.0 / (incorrect but needed by old programs)
PA = 1.29763632687E+000 / [deg, 0-360 CCW] Position angle of plate
CTYPE1 = 'RA---TAN' / X-axis coordinate type
CRVAL1 = 3.14341739025E+002 / X-axis coordinate value
CRPIX1 = 7.68000000000E+002 / X-axis reference pixel
CDELT1 = -2.59534986961E-004 / [deg/pixel] X-axis plate scale
CROTA1 = -1.29763632687E+000 / [deg] Roll angle wrt X-axis
CTYPE2 = 'DEC--TAN' / Y-axis coordinate type
CRVAL2 = 4.03127760707E+001 / Y-axis coordinate value
CRPIX2 = 7.68000000000E+002 / Y-axis reference pixel
CDELT2 = -2.59455750274E-004 / [deg/pixel] Y-Axis Plate scale
CROTA2 = -1.29763632687E+000 / [deg] Roll angle wrt Y-axis
CD1_1 = -2.59468427764E-004 / Change in RA---TAN along X-Axis
CD1_2 = -5.87565834781E-006 / Change in RA---TAN along Y-Axis
CD2_1 = 5.87745274898E-006 / Change in DEC--TAN along X-Axis
CD2_2 = -2.59389211397E-004 / Change in DEC--TAN along Y-Axis
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