1.4.1.0 measures.measure

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measures.measure - Function

1.4.1 convert a measure to another reference

Description

measure converts measures (epoch, direction etc.) from one reference to another. It will, for instance, convert a direction from J2000 to AZEL representation.
Its arguments are a measure, an output reference code (see the individual measures for the allowable codes (direction, position, epoch, frequency, doppler, radialvelocity, baseline, uvw, earthmagnetic)), and an optional offset of the same type as the main measure. The offset will be subtracted from the result before it is returned.
In some cases (see the individual measures for when), more information than just a reference code is necessary. E.g. the above example of a conversion to AZEL, needs to know for when, and where on Earth we want it. This information is stored in a reference frame. Measures are set in the reference frame with the doframe function. The frame is tool wide.
IMPORTANT NOTE:
To get an accurate conversion of solar system objects direction to a celestial frame, one should convert to AZEL or HADEC before to get parallax accounted for. Thus if you want to get the moon’s position in J2000..one would do it in 2 stages
i.e (after setting the appropriate frames)
moonazel=me.measure(me.direction(’moon’), ’AZELGEO’) moonJ2000=me.measure(moonazel, ’J2000’)

Arguments


Inputs
v	measure to be converted
	allowed:	record
	Default:
rf	output reference code
	allowed:	string
	Default:
off	optional output offset measure
	allowed:	record
	Default:

Returns
record

Example

print "\t----\t measure Ex 1 \t----"
a = me.epoch(’utc’,’today’)         # a time
print a
#{’m0’: {’value’: 54054.872957673608, ’unit’: ’d’},
# ’refer’: ’UTC’,
# ’type’: ’epoch’}
print me.doframe(me.source(’1934-638’))
print me.measure(a, ’tai’) # convert to IAT
#{’m0’: {’value’: 54054.873339618054, ’unit’: ’d’},
# ’refer’: ’TAI’,
# ’type’: ’epoch’}
print me.doframe(a) # set time in frame
#True
print me.doframe(me.observatory(’ALMA’)) # set position in frame
#True
b=me.direction(’j2000’, qa.toangle(’0h’), ’-30deg’)  # a direction
print b
#{’m0’: {’value’: 0.0, ’unit’: ’rad’},
# ’m1’: {’value’: -0.52359877559829882, ’unit’: ’rad’},
# ’refer’: ’J2000’,
# ’type’: ’direction’}
print me.measure(b, ’azel’) # convert to AZEL
#{’m0’: {’value’: 1.9244096810822324, ’unit’: ’rad’},
# ’m1’: {’value’: 0.76465385681363052, ’unit’: ’rad’},
# ’refer’: ’AZEL’,
# ’type’: ’direction’}
print qa.angle(me.getvalue(me.measure(b,’azel’))[’m0’])     # show as angles
#[’+110.15.38’]
print qa.angle(me.getvalue(me.measure(b,’azel’))[’m1’])
#[’+043.48.41’]

Another example:

print "\t----\t measure Ex 2 \t----"
# Fill the frame with necessary information
print me.doframe(me.epoch(’utc’,’today’))
#True
print me.doframe(me.observatory(’ALMA’))
#True
print me.doframe(me.direction(’mars’))
#True
a=qa.unit(’1GHz’)
print a
#{’value’: 1.0, ’unit’: ’GHz’}
m=me.frequency(’lsrk’,qa.quantity(qa.getvalue(a),qa.getunit(a)))
print m
#{’m0’: {’value’: 1000000000.0, ’unit’: ’Hz’},
# ’refer’: ’LSRK’,
# ’type’: ’frequency’}
print me.measure(m,’lsrd’)
#{’m0’: {’value’: 1000001766.3928765, ’unit’: ’Hz’},
# ’refer’: ’LSRD’,
# ’type’: ’frequency’}

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