coordsys - Constructor

Create a default coordsys tool

Synopsis
coordsys(direction, spectral, stokes, linear, tabular)

Arguments

direction	in	Make a direction coordinate ?
		Allowed:	Bool
		Default:	F
spectral	in	Make a spectral coordinate ?
		Allowed:	Bool
		Default:	F
stokes	in	Make a Stokes coordinate with these Stokes
		Allowed:	String or vector of Strings
		Default:	""
linear	in	Make a linear coordinate with this many axes
		Allowed:	Integer
		Default:	0
tabular	in	Make a tabular coordinate
		Allowed:	Bool
		Default:	F

Returns
Coordsys tool or fail

Description

By default, this constructor makes an empty Coordsys tool. You can ask it to include various sorts of coordinates through the arguments. Except for Stokes, you don't have any control over the coordinate contents (e.g. reference value etc.) it does make for you on request. But you can edit the Coordinate System after creation if you wish.

If you wish to make a Stokes coordinate, then you assign stokes to a string (or a vector of strings) saying which Stokes you want. AIPS++ allows rather a lot of potential Stokes types.

Probably most useful is some combination of the basic I, Q, U, V, XX, YY, XY, YX, RR, LL, RL, and LR.

However, a more esoteric choice is also possible: RX, RY, LX, LY, XR, XL, YR, YL (these are mixed linear and circular), PP, PQ, QP, QQ (general quasi-orthogonal correlation products) RCircular, LCircular, Linear (single dish polarization types).

You can also specify some polarization `Stokes' types: Ptotal (Polarized intensity (( Q² + U² + V²)⁽1/2)), Plinear (Linearly Polarized intensity ( (Q² + U²)⁽1/2)), PFtotal (Polarization Fraction (Ptotal/I)), PFlinear (Linear Polarization Fraction (Plinear/I)), and Pangle (Linear Polarization Angle ( 0.5arctan(U/Q) in radians)).

Probably you will find the more unusual types aren't fully supported throughout the system.

You can make a LinearCoordinate with as many uncoupled axes as you like. Thus, linear=2 makes one LinearCoordinate with 2 axes (think of it like a DirectionCoordinate which also has 2 axes [but coupled in this case], a longitude and a latitude).

If you make a TabularCoordinate, it is linear to start with. You can change it to a non-linear one by providing a list of pixel and world values to function settabular.

Example

- cs := coordsys()
- cs.ncoordinates()
0
- cs.done()
- cs
F
#
- cs2 := coordsys(direction=T, stokes='I V');
- cs2.ncoordinates()
2
- cs2.coordinatetype()
Direction Stokes
#
- cs2.summary()
Direction system : J2000
Telescope        : ATCA
Observer         : Karl Jansky
Date observation : 2000/07/03/08:10:57

Axis Type      Name             Proj   Coord value at pixel    Coord incr Units
------------------------------------------------------------------------------- 
1    Direction Right Ascension   SIN  00:00:00.000     1.00 -6.000000e+01 arcsec
2    Direction Declination       SIN +00.00.00.000     1.00  6.000000e+01 arcsec
3    Stokes    Stokes                           IV

The second Coordinate System contains a direction coordinate and a Stokes coordinate. This means that there are three `axes' associated with the 2 coordinates.

Next: coordsys.axesmap - Function Up: coordsys - Tool Previous: coordsys - Tool Contents Index

	Package	general
	Module	images
	Tool	coordsys