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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
Returns
record

Example

"""
#
print "\t----\t torel Ex 1 \t----"
csys = cs.newcoordsys(direction=T, spectral=T)
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=T, spectral=T)
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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