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coordsys.setspectral - Function

1.1.3 Set tabular values for the spectral coordinate


Description

When you construct a Coordsys tool, if you include a Spectral Coordinate, it will be linear in frequency. This function allows you to replace the Spectral Coordinate by a finite table of values. Coordinate conversions between pixel and world are then done by interpolation.

You may specify either a vector of frequencies or velocities. If you specify frequencies, you can optionally specify a (new) reference code (see function setreferencecode for more details) and rest frequency (else the existing ones will be used).

If you specify velocities, you can optionally specify a (new) reference code and rest frequency (else the existing ones will be used). You must also give the doppler type (see function summary for more details). The velocities are then converted to frequency for creation of the Spectral Coordinate (which is fundamentally described by frequency).

You may specify the rest frequency as a Quantum or a double (native units of Spectral Coordinate used).

Arguments





Inputs

refcode

Reference code. Leave unset for no change.

allowed:

string

Default:

restfreq

Rest frequency. Leave unset for no change.

allowed:

any

Default:

variant

frequencies

Vector of frequencies. Leave unset for no change.

allowed:

any

Default:

variant 1GHz

doppler

Doppler type. Leave unset for no change.

allowed:

string

Default:

velocities

Vector of velocities types. Leave unset for no change.

allowed:

any

Default:

variant 1km/s

Returns
bool

Example

 
 
print "\t----\t setspectral Ex 1 \t----"  
csys = cs.newcoordsys(spectral=T);  
f1 = [1,1.01,1.03,1.4]  
fq = qa.quantity(f1, ’GHz’)  
csys.setspectral(frequencies=fq)  
v = csys.frequencytovelocity(f1, ’GHz’, ’radio’, ’km/s’)  
print ’v=’, v  
#v= [88731.317461076716, 86620.706055687479, 82399.483244909003, 4306.8612455073862]  
vq = qa.quantity(v, ’km/s’)  
csys.setspectral(velocities=vq, doppler=’radio’)  
f2 = csys.velocitytofrequency(v, ’GHz’, ’radio’, ’km/s’)  
print ’f1 = ’, f1  
#f1 =  [1, 1.01, 1.03, 1.3999999999999999]  
print ’f2 = ’, f2  
#f2 =  [1.0, 1.01, 1.03, 1.3999999999999999]  
 
We make a linear Spectral Coordinate.  Then overwrite it with  
a list of frequenices.  Convert those values to velocity,  
then overwrite the coordinate starting with a list of  
velocities. Then convert the velocities to frequency  
and show we get the original result.  

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