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NRAO Home > CASA > CASA Toolkit Reference Manual |
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coordsys.torel - Function
1.1.3 Convert absolute coordinate to relative
Description
This function converts an absolute coordinate to a relative coordinate. The
coordinate may be a pixel coordinate or a world coordinate.
Relative coordinates are relative to the reference pixel (pixel coordinates) or the reference value (world coordinates) in the sense relative = absolute - reference.
If the coordinate is a pixel coordinate, it is supplied as a numeric vector. If the coordinate is a world coordinate, you may give it in all of the formats described in the formatting discussion.
If the coordinate value is supplied by a Coordsys tool function (e.g. toworld) then the coordinate ’knows’ whether it is world or pixel (and absolute or relative). However, you might supply the value from some other source as a numeric vector (which could be world or pixel) in which case you must specify whether it is a world or pixel coordinate via the isworld argument.
Arguments
Inputs |
| ||
value |
| Absolute coordinate | |
| allowed: | any |
|
| Default: | variant |
|
isworld |
| Is coordinate world or pixel? Default is unset.
| |
| allowed: | int |
|
| Default: | -1 |
|
record
Example
"""
#
print "\t----\t torel Ex 1 \t----"
csys = cs.newcoordsys(direction=True, spectral=True)
aw = csys.toworld([99,99,23], ’s’)
rw = csys.torel(aw)
aw2 = csys.toabs(rw)
print aw
#{’ar_type’: ’absolute’, ’pw_type’: ’world’,
# ’string’: array([’23:53:23.78086843’, ’+01.39.00.82133427’,
# ’1.41502300e+09 Hz’], dtype=’|S19’)}
print rw
#{’ar_type’: ’relative’, ’pw_type’: ’world’,
# ’string’: array([’-5.94082202e+03 arcsec’, ’5.94082133e+03 arcsec’,
# ’2.30000000e+04 Hz’], dtype=’|S23’)}
print aw2
#{’ar_type’: ’absolute’, ’pw_type’: ’world’,
# ’string’: array([’23:53:23.78086818’, ’+01.39.00.82133000’,
# ’1.41502300e+09 Hz’], dtype=’|S19’)}
#
"""
This example uses world coordinates.
"""
#
print "\t----\t torel Ex 2 \t----"
csys = cs.newcoordsys(direction=True, spectral=True)
ap = csys.topixel() # Reference value
rp = csys.torel(ap)
ap2 = csys.toabs(rp)
print ap
#{’ar_type’: ’absolute’, ’pw_type’: ’pixel’, ’numeric’: array([ 0., 0., 0.])}
print rp
#{’ar_type’: ’relative’, ’pw_type’: ’pixel’, ’numeric’: array([ 0., 0., 0.])}
print ap2
#{’ar_type’: ’absolute’, ’pw_type’: ’pixel’, ’numeric’: array([ 0., 0., 0.])}
#
"""
This example uses pixel coordinates.
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Copyright © 2016 Associated Universities Inc., Washington, D.C.
This code is available under the terms of the GNU General Public Lincense
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