SizeMagDiagram

The Code

import numpy

import esutil as eu

import biggles

run='wlse0003'

exposure='decam--24--37-i-7'

ccd = 62

dir='$DESDATA/wlbnl/%s/%s' % (run,exposure)

starfile = '%s/%s_%s_%s_stars.fits' % (dir,run,exposure,ccd)

# eu.io.read will expand the $DESDATA environment variable. Note, it also

# returns a plain ndarray, for which you access fields dictionary style

# data['fieldname']. If you prefer record style data.fieldname send

# view=numpy.recarray, but note that field names can get clobbered by array

# attributes!

print 'Reading findstars output: ',starfile

fsdata = eu.io.read(starfile,ext=1)

# make a size-mag diagram

plt = biggles.FramedPlot()

# all points

points = biggles.Points( fsdata['mag'], fsdata['sigma0'] )

points.label = 'all'

# those we used for PSF stars

w, = numpy.where( fsdata['star_flag'] == 1)

psf_points = biggles.Points( fsdata['mag'][w], fsdata['sigma0'][w],color='red' )

psf_points.label = 'PSF stars'

k = biggles.PlotKey( .1, .9, [points,psf_points] )

plt.add(points, psf_points, k)

plt.xlabel = 'i-mag'

plt.ylabel = r'$\sigma_0$'

plt.xrange = 8,18.5

plt.yrange = 0,3

# to view interactively

plt.show()

# write to encapsulated postscript

plt.write_eps('sizemag.eps')

# or png. Note you usually get better results writing the postscript and then

# converting it to png

plt.write_img(600,600,'sizemag.png')

The Output

Here is the post script output: sizemag.eps

Here is the .eps file converted to png:

And this is the result of the write_img(), which is less nice. There may be options

to improve this however.