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coordsys.setincrement - Function

	Package	general
	Module	images
	Tool	coordsys

Set the increment

Synopsis
setincrement(value, type)

Arguments

value	in	Increments
		Allowed:	Vector of doubles, vector of quantities, quantity of vector of doubles, vector of string, record
type	in	Which coordinate type ?
		Allowed:	String from "direction", "stokes", "spectral", "linear", "tabular" or unset
		Default:	All

Returns
T or fail

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 (short-hand name si) 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 dq.quantity([-1,2],'arcsec').

You can recover the current increments with function increment.

Example

- cs := coordsys(direction=T, spectral=T)
- rv := cs.increment(format='q')
- rv
[__*0=[value=-1, unit='], __*1=[value=1, unit='], __*2=[value=1000, unit=Hz]] 
-
- rv2 := dq.quantity('4kHz');
- cs.setincrement(value=rv2, type='spec')
- cs.increment(type='spec', format='q')
[value=4000, unit=Hz] 
-
- cs.increment(format='q')
[__*0=[value=-1, unit='], __*1=[value=1, unit='], __*2=[value=4000, unit=Hz]] 
-
- cs.setincrement (value="-2' 2' 2e4Hz")
- cs.increment(format='q')
[__*0=[value=-2, unit='], __*1=[value=2, unit='], __*2=[value=20000, 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.