==========================
2016-05-12: New Maintainer
==========================

Ed Santiago can no longer maintain this code: he hasn't worked
with IDL, or even had access to it, since 2000. Please contact
Ryan Boller < ryan.a.boller at nasa dot gov > for support.

-------------------------------------------------------------------------

This is Ed's "cxform" package, for transforming between coordinate frames.

The latest version of this package should be available at

	http://www.nis.lanl.gov/~esm/idl/cxform/


=======================
Using the code from IDL
=======================

The function prototype is

	new = CXFORM( pos, source_frame, dest_frame, time )

where:
	pos		is a vector of length 3, containing the position
			in source_frame coordinates.

	source_frame	is an ASCII string naming the source
			coordinate system, e.g., 'GSE', 'J2000'

	dest_frame	is also an ASCII string, naming the destination
			coordinate system.

	time		is "ephemeris seconds past J2000 (1 Jan 2000 12:00)".
			Not the most convenient time unit for you, I 
			suppose, but it is for me.


	new		is the position, in dest_frame coordinates.


For example:

	IDL> spice_init_generic		; to initialize SPICE, for STR2ET
	IDL> cspice_str2et, '1999 Sep 30 07:05', et
	IDL> pos = cxform([1,0,0], 'GSE', 'GEO', et)
	IDL> help,pos
	POS             DOUBLE    = Array[3]
	IDL> print,pos
	      0.32476279      0.94466059    -0.046319448
	IDL> 


=======================
Coordination Animations
=======================

The IDL program COORD_ANIM can be used to display an animation on your 
screen, showing the relationships between two coordinate systems.

The default animation steps through one hour at a time.  This brings
out the effect of Earth's rotation.  For some coordinate systems,
this effect is nonexistent, and only serves to slow things down 
a lot.  For instance, the GSE axes do not vary much over one day,
whereas the GEO ones do.

For that reason, you can use the "STEP" keyword to specify the number
of hours in each step.


Here are some useful ones to try:

	coord_anim, 'GSE', 'GSM', step=24
	coord_anim, 'GSE', 'GEI', step=24
	coord_anim, 'GSE', 'GEO', step=1

...but remember, you can give it any two you like.