1.1.3.0 coordsys.setincrement

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coordsys.setincrement - Function

1.1.3 Set the increment

Description

Each axis associated with the Coordinate System has a reference value, reference pixel and an increment (per pixel). These are used in the mapping from pixel to world coordinate.

This function allows you to set a new increment. You should not do this on ”stokes” axes unless you are an adept or a big risk taker.

You can set the increments either for all axes (type=unset) or for just the axes associated with a particular coordinate type.

You may supply the increments in all of the formats described in the formatting discussion.

In addition, you can also supply the increments as a quantity of vector of doubles. For example qa.quantity([-1,2],’arcsec’).

You can recover the current increments with function increment.

Arguments


Inputs
value	Increments
	allowed:	any
	Default:	variant
type	Coordinate type: ”direction”, ”stokes”, ”spectral”, ”linear”, ”tabular”. Leave empty for all
	allowed:	string
	Default:

Returns
bool

Example

"""
#
print "\t----\t setincrement Ex 1 \t----"
csys=cs.newcoordsys(direction=T, spectral=T)
rv = csys.increment(format=’q’)
print rv
# {’ar_type’: ’absolute’, ’pw_type’: ’world’,
# ’quantity’: {’*1’: {’value’: -1.0, ’unit’: "’"},
#              ’*2’: {’value’: 1.0, ’unit’: "’"},
#              ’*3’: {’value’: 1000.0, ’unit’: ’Hz’}}}
rv2 = qa.quantity(’4kHz’);
csys.setincrement(value=rv2, type=’spec’)
print csys.increment(type=’spec’, format=’q’)
#{’ar_type’: ’absolute’, ’pw_type’: ’world’,
# ’quantity’: {’*1’: {’value’: 4000.0, ’unit’: ’Hz’}}}
csys.setincrement(value=’5kHz’, type=’spec’)
print csys.increment(type=’spec’, format=’q’)
#{’ar_type’: ’absolute’, ’pw_type’: ’world’,
# ’quantity’: {’*1’: {’value’: 5000.0, ’unit’: ’Hz’}}}
print csys.increment(format=’q’)
#{’ar_type’: ’absolute’, ’pw_type’: ’world’,
# ’quantity’: {’*1’: {’value’: -1.0, ’unit’: "’"},
#              ’*2’: {’value’: 1.0, ’unit’: "’"},
#              ’*3’: {’value’: 5000.0, ’unit’: ’Hz’}}}
csys.setincrement (value="-2’ 2’ 2e4Hz")
print csys.increment(format=’q’)
#{’ar_type’: ’absolute’, ’pw_type’: ’world’,
# ’quantity’: {’*1’: {’value’: -2.0, ’unit’: "’"},
#              ’*2’: {’value’: 2.0, ’unit’: "’"},
#              ’*3’: {’value’: 20000.0, ’unit’: ’Hz’}}}
#
"""

In the example we first recover the increments as a vector of
quantities. We then create a quantity for a new value for the spectral
coordinate increment.  Note we use units of kHz whereas the spectral
coordinate is currently expressed in units of Hz.  We then set the
increment for the spectral coordinate.  We then recover the increment
again; you can see 4kHz has been converted to 4000Hz.  We also show
how to set the increment using a string interface.

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