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coordsys.setspectral - Function

	Package	general
	Module	images
	Tool	coordsys

Set tabular values for the spectral coordinate

Synopsis
setspectral(refcode, restfreq, frequencies, doppler, velocities)

Arguments

refcode	in	Reference code
		Allowed:	String
		Default:	No change
restfreq	in	Rest frequency
		Allowed:	Quantum or double
		Default:	No change
frequencies	in	Vector of frequencies
		Allowed:	Quantum vector
		Default:	No change
doppler	in	Doppler type
		Allowed:	String
		Default:	No change
velocities	in	Vector of velocitiestypes
		Allowed:	Quantum vector
		Default:	No change

Returns
T or fail

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).

Example

- cs := coordsys(spectral=T);
-
- f1 := [1,1.01,1.03,1.4]
- fq := dq.quantity(f1, 'GHz')
- cs.setspectral(frequencies=fq)
- v := cs.frequencytovelocity(f1, 'GHz', 'radio', 'km/s')
- print 'v=', v
[88731.3175 86620.7061 82399.4832 4306.86125]  
- vq := dq.quantity(v, 'km/s')
- cs.setspectral(velocities=vq, doppler='radio')
- f2 := cs.velocitytofrequency(v, 'GHz', 'radio', 'km/s')
-
- print 'f1 = ', f1
[1 1.01 1.03 1.4]  
- print 'f2 = ', f2
[1 1.01 1.03 1.4]

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.