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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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