NAME:
	CenterOfMass
 PURPOSE:
	Calculate center of mass of a distribution of masses in n dimensions
 CATEGORY:
	gen/idl/toolbox
 CALLING SEQUENCE:
	FUNCTION CenterOfMass, mass_array, loc_array
 INPUTS:
	mass_array	array of any structure; type: integer or float
 OPTIONAL INPUT PARAMETERS:
	loc_array	array[n, size(mass_array,/dim)]
			    i.e. same structure as mass_array with one extra
			    leading dimension
 OUTPUTS:
	P		scalar, or array[n]; double precision
			    coordinates of center of mass. In the one-dimensional
			    case (n=1) a scalar is returned.
 INCLUDE:
	@compile_opt.pro		; On error, return to caller
 CALLS: ***
	SubArray, SyncDims
 CALLED BY:
	even_light, qImage_cw_ZEllipse, qImage_cw_ZUpdate, wedge_content
 SIDE EFFECTS:
	The center of mass calculation is done in double precision.
 PROCEDURE:
	Two separate cases are calculated:
 >	1. Only the mass_array is specified as an n-dimensional array.
	    The center of mass is returned as an n-element array (scalar if n=1).
	    The array index in each dimension is used as the distance scale:
		mass_array = [[1,2],[3,4]]
		P = centerofmass(mass_array)
	    results in
		P = [0.6,0.7]
 >	2. If both mass_array and loc_array are specified then loc_array, with
		leading dimension of n elements, specifies the n-dimensional locations
		of the masses in mass_array, e.g. in the 3-dimensional case, if mass_array
		is a 10x10 array then loc_array would be a 3x10x10 array, with
		loc_array[0,*,*] the x-coordinate, loc_array[1,*,*] the y-coordinate and
		loc_array[2,*,*] the z-ccordinate.
	    The above example again:
		mass_array = [1,2,3,4]
		loc_array  = [[0,0],[1,0],[0,1],[1,1]]
		P = centerofmass(mass_array)
	    results in
		P = [0.6,0.7]
 MODIFICATION HISTORY:
	NOV-1999, Paul Hick (UCSD/CASS)
	FEB-2000, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    internally the procedure converts the mass array to a normalized mass by
	    dividing by the total mass. This results in a divide by zero if the sum is
	    zero (presumably because all masses are zero). To avoid this one unit is
	    added to each mass.

 NAME:
       CheckDir
 PURPOSE:
       Check whether a directory exists
 CATEGORY:
	Environment
 CALLING SEQUENCE:
	FUNCTION CheckDir, Name, LongName, stay=stay, silent=silent
 INPUTS:
	Name	    scalar string, the directory name
			Name='' always returns status=1B with
			LongName set to the current directory.
 OPTIONAL INPUT PARAMETERS:
	/stay	    if set then a 'cd' to the directory is made (if it exists)
 OUTPUTS:
	Status	    0 : directory doesn't exist
		    1 : directory exists
 OPTIONAL OUTPUT PARAMETERS:
	LongName    scalar string
		Status=0 : null string
		Status=1 : fully qualified directory name
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLED BY:
	FindAllSubDirs, RemoteView_Display2D, RemoteView_Display3D, SetFileSpec
	getnagoyasources, getootyasources, getsmeisources, hide_env, mk_flick
	nagoya_glevel, qImage_cw_SmeiMask, qView_FileFilter, skyd_cat, skyd_version
	smei_base_testcase, smei_buf, smei_buf_get, smei_buf_getframe, smei_buf_mget
	smei_buf_prep, smei_filepath, smei_frm_cp, smei_frm_findpoint, smei_frm_summary
	smei_frm_write, smei_getfile, smei_hdr_get, smei_hdr_make, smei_hdr_plot
	smei_mkcal_auto, smei_mkmask, smei_mkorb, smei_mksidereal, smei_orbit_stats
	smei_sky_track, smei_star_fitone, smei_star_remove, smei_www_skymaps
	smei_zld_remove [1], smei_zld_remove [2], smeidb_mounted, unhide_env
	vu_get_page, vu_image, vu_movie, vu_quick_movie, www_help, www_help_rsi
 RESTRICTIONS:
 >	No attempt is made to pre-process the input directory name
	(such as translation of logicals/env. variables, etc.)
 CALLS: ***
	FILEPATH, InitVar, hide_env, who_am_i
 PROCEDURE:
 >	CD is used to decide whether a directory exists, and is
	used to retrieve the full directory name.
 >	filepath is called to make sure a trailing (back)slash is appended on
	Unix and Windows systems.
 MODIFICATION HISTORY:
	DEC-1997, Paul Hick
	SEP-2002, Paul Hick (UCSD/CASS)
	    Return zero if input spec contains wildcard.
	FEB-2008, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Added name of calling routine to informational message.

 NAME:
	clock
 PURPOSE:
	Display time of day (including day of year (DOY) and Julian day number (JD)
 CATEGORY:
	Totally unnecessary
 CALLING SEQUENCE:
	PRO clock
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	TimeGet, TimeSet
 MODIFICATION HISTORY:
	JAN-2004, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CombineRotations
 PURPOSE:
	Combine two rotations, i.e. find the rotation resulting from
	first applying one (R1), then another (R2) rotation.
 CATEGORY:
	gen/idl/toolbox/math
 CALLING SEQUENCE:
	FUNCTION CombineRotations, R1, R2, R3, R4, R5, $
	    quaternion	= quaternion	, $
	    euler_angles= euler_angles	, $
	    dcm 	= dcm		, $
	    geometric	= geometric	, $
	    degrees	= degrees
 INPUTS:
	R1		array[3,n], array[4,n], array[3,3,n]; type: float
			    first rotation
	R2		array[3,m], array[4,m], array[3,3,m]; type: float
			    second rotation

			R1 and/or R2 can be a single rotation with the other
			multiple rotations, i.e. n = 1 and m != 1; or n != 1
			and m = 1. The single rotation will be combined with
			each of the multiple rotations.

	R3,R4,R5	Additional rotations. Up to 5 rotations can be combined
			in a single call.
 OPTIONAL INPUT PARAMETERS:
	/quaternion	input and output rotations are in quaternions;
	/euler_angles	in- and output rotations are in Euler angles triplets
	/dcm		in- and output rotations are in direction cosine matrices
	/geometric	in- and putput rotations are in geometic form
			    (unit vector, plua rotation around unit vector).

	/degrees	if set then all angles are in degrees (default: radians)
 OUTPUTS:
	R		array[3,n > m]; type: same as input
			    combined rotation in same form as input
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	CvRotation, InitVar, IsType, SyncArgs
 CALLED BY:
	CvSky, CvSky_Galactic, smei_cam_quaternion, smei_camera, smei_frm_where
	smei_orient_test, vu_linecut, vu_planarcut, vu_spherecut
 SEE ALSO:
	EulerRotate
 PROCEDURE:
	See definition of quaternions in: Foley, van Dam, Feiner and Hughes
	'Computer graphics, principles and practice', 2nd edition.
	Addison-Wesley, 1992, page 1063
 MODIFICATION HISTORY:
	MAR-2003, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	compile_opt
 PURPOSE:
	Controls default IDL error handler and special compiler options
 CALLING SEQUENCE:
	@compile_opt.pro
 PROCEDURE:
	Included in virtually all IDL procedures in the SSW_SMEI tree
 MODIFICATION HISTORY:
	JAN-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	cv
 CALLING SEQUENCE:
	PRO cv
 INCLUDE:
	@compile_opt.pro
 CALLS: ***
	AngleRange, TimeSet, WhatIs, big_eph, ra_fictitious_sun, sgp4_orbit_axis
	sphere_distance, txt_read

 NAME:
	CvPrecess
 PURPOSE:
	Converts equatorial or ecliptic coordinates for epoch UT1 to
	epoch UT2, i.e. corrects for precession between the two epochs.
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvPrecess, UT1, UT2, pos   , $
	    degrees	    = degrees	    , $
	    from_ecliptic   = from_ecliptic , $
	    to_ecliptic     = to_ecliptic   , $
	    rectangular     = rectangular
 CALLS: ***
	CvSky, CvSky_Precess, EulerRotate, InitVar, REVERSE
 INPUTS:
	UT	    array[n]; type: time structure
			initial epoch
	UT	    array[n]; type: time structure
			final epoch
	pos[2,n] or pos[3,n]
		    spherical coordinates at start epoch UT1
		    RA or longitude, declination or latitude, and, optional
		    the distance (the distance is not modified)
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set, all angles are in degrees
	/from_ecliptic
	/to_ecliptic
		    by default the input and output are assumed to be in
		    equatorial coordinates (RA and declination).
		    If /from_ecliptic is set then the input is assumed to be
		    in ecliptic coordinates (longitude and latitude)
		    If /to_ecliptic is set then the output is in ecliptic
		    coordinates
 OUTPUTS:
	pos[2,n] or pos[3,n]
		    spherical coordinates at final epoch UT2
		    RA or longitude, declination or latitude, and, optional
		    the distance (the distance is not modified)
 INCLUDE:
	@compile_opt.pro
 CALLS: ***
	CvSky, CvSky_Precess, EulerRotate, InitVar, REVERSE
 CALLED BY:
	big_eph, getnagoyasources, getootyasources, getsmeisources, jpl_eph, jpl_test
	mpc_eph, mpc_orbit_eph, sgp4_eph, smei_sky, usno_eph
 PROCEDURE:
	See R. Green, Spherical Astronomy, Cambridge UP, 1985, Sect. 9.5, p. 217
	(1) First transform ecliptic longitude and latitude to equatorial right
	    ascension and declination (for initial epoch);
	(2) Transform equatorial coordinates for initial epoch to epoch J2000.0;
	(3) Calculate equatorial coordinates for epoch J2000.0 to final epoch;
	(4) Transform back to ecliptic coordinates (for final epoch).
 MODIFICATION HISTORY:
	DEC-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Adapted from Fortran subroutine PRECESSION_ROT

 NAME:
	CvRotation
 PURPOSE:
	Convert between several ways of specifying rotations
 CATEGORY:
	gen/idl/toolbox/math
 CALLING SEQUENCE:
	FUNCTION CvRotation, $
	    from_euler	    = from_euler	, $
	    from_quaternion = from_quaternion	, $
	    from_dcm	    = from_dcm		, $
	    from_geometric  = from_geometric	, $
	    to_euler	    = to_euler		, $
	    to_quaternion   = to_quaternion	, $
	    to_dcm	    = to_dcm		, $
	    to_geometric    = to_geometric	, $
	    degrees	    = degrees
 INPUTS:
 OPTIONAL INPUT PARAMETERS:
	Only one of the from_* keywords is specified:

	from_euler=from_euler
		    array[3,n]; type: real
			triplets of Euler angles
	from_quaternion=from_quaternion
		    array[4,n]; type: real
			unit quaternion quatruplets with the scalar in array[3,n]
			(MUST be unit quanternion)
	from_dcm    array[3,3,n]; type: float
			direction cosine matrices
	from_geometric
		    array[3,n] or array[4,n]
			unit vector, plus angle of rotation around unit vector.
			array[3,n]: phase angle, latitude and angle of rotation
			array[4,n]: rectangular coordinates and angle of rotation

	Only one of the /to_* keywords is specified:

	/to_euler   if set then the output is an array[3,n] of Euler angles
	/to_quaternion
		    if set then the output is an array[4,n] on unit quaternions
	/to_dcm     if set then direction cosine matrices array[3,3,n] are returned
	/to_geometric
		    if set then a unit vector in rectangular coordinates and an
			angle of rotation around the unit vector, array[4,n]
			are returned.

	/degrees    if set, all angles are in degrees (default: radians)
 OUTPUTS:
	out	    array[3,n], array[4,n]; type: same as input
			Euler angles, unit quaternion, direction cosine matrix
			or unit vector with angle of rotation.
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	AngleRange, CV_COORD, InitVar, IsType, ToRadians, boost
 CALLED BY:
	CombineRotations, CvSky_Galactic, cvsmei, smei_ccd2sky, smei_frm_where
	smei_orient_test, smei_sgp4_quat, smei_sky2cam
 SEE ALSO:
	EulerRotate
 RESTRICTIONS:
	The quaternion to Euler angle conversion may still have problems near qx = qy = 0
	(rotations around the z-axis) and q0 = qz = 0 (rotations around axis in x-y plane.
	The singularities themselves (strictly qx=qy=0 and strictly q0=qz=0) are dealt
	with properly.
 PROCEDURE:
	The Euler angle triplets define rotation around z-axis, y-axis and
	z-axis respectively.

	A specific rotation can be specified by more then one set of Euler
	angles or quaternions. For Euler angles [pi+alfa, -beta, pi+gamma] is the same
	rotation as [alfa, beta, gamma]. For quaternions [-qx,-qy,-qz,-q0] is the same
	rotation as [qx,qy,qz,q0]. If q = cos(phi/2)+sin(phi/2)*u and
	-q = cos(chi/2)+sin(chi/2)*v (for unit vectors u and v), then v=-u and
	chi/2=180-phi/2, i.e. chi=360-phi. So -q is a rotation over -phi after changing
	the sign of the rotation vector.

	The conversion /to_euler always returns a positive beta in [0,180].
 MODIFICATION HISTORY:
	FEB-2003, Paul Hick (UCSD/CASS)
	MAR-2003, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Rewrite. Moved scalar quaternion component from first to last position
	    Improved calculation of quaternions from DCM or Euler angles
	    (avoiding singularities for q0 close to zero).

 NAME:
	CvSky
 PURPOSE:
	Converts between ecliptic, heliographic, equatorial and geographic
	coordinates
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky, UT, fromvectors 	, $
	    from_ecliptic   = from_ecliptic	, $
	    from_centered_ecliptic= from_centered_ecliptic, $
	    from_equatorial = from_equatorial	, $
	    from_galactic   = from_galactic	, $
	    from_heliographic= from_heliographic, $
	    from_centered_heliographic= from_centered_heliographic, $
	    from_geographic = from_geographic	, $
	    from_gse	    = from_gse		, $
	    from_gsm	    = from_gsm		, $
	    from_rtn	    = from_rtn		, $
	    from_ihg	    = from_ihg		, $

	    to_ecliptic     = to_ecliptic	, $
	    to_centered_ecliptic= to_centered_ecliptic, $
	    to_equatorial   = to_equatorial	, $
	    to_galactic     = to_galactic	, $
	    to_heliographic = to_heliographic	, $
	    to_centered_heliographic= to_centered_heliographic	, $
	    to_geographic   = to_geographic	, $
	    to_rtn	    = to_rtn		, $
	    to_gse	    = to_gse		, $
	    to_gsm	    = to_gsm		, $
	    to_ihg	    = to_ihg		, $

	    heliocentric    = heliocentric	, $
	    bodycentric     = bodycentric	, $

	    degrees	    = degrees		, $
	    rectangular     = rectangular	, $

	    euler_angles    = euler_angles	, $
	    euler_info	    = euler_info	, $
	    silent	    = silent
 INPUTS:
	UT		array; type: standard time structure
			    times (UT); Note that if /rectangular is set then UT
			    can only be an array[1]
			    (i.e. a single time must be specified)
	fromvectors	array;
 OPTIONAL INPUTS:
	from_ecliptic	= from_ecliptic
	from_centered_ecliptic = from_centered_ecliptic
	from_heliographic= from_heliographic
	from_centered_heliographic= from_centered_heliographic
	from_geographic = from_geographic
	from_equatorial = from_equatorial
	from_rtn	= from_rtn
	from_gse	= from_gse
	from_gsm	= from_gsm
	from_ihg	= from_ihg
			array [2,n] or array[3,n]
			    /rectangular NOT set: In[0,*] is longitude, In[1,*] is latitude;
						In[2,*] (optional?) is radial distance
			    /rectangular set: rectangular (x,y,z) coordinates

			Alternatively, fromvectors contains the input vectors and the
			appropriate keyword /from* is SET.

	/to_ecliptic	    conversion to ecliptic coordinates
	/to_centered_ecliptic
			    conversion to sun-centered ecliptic coordinates
			    (/heliocentric NOT set) or earth-centered ecliptic
			    coordinates (/heliocentric SET)
	/to_heliographic    conversion to heliographic coordinates
	/to_centered_heliographic
			    conversion to earth-centered heliographic coordinates
	/to_geographic	    conversion to geographic coordinates
	/to_equatorial	    conversion to equatorial ccordinates
	/to_rtn 	    conversion to magnetic RTN coordinates
	/to_gse 	    conversion to magnetic GSE coordinates
	/to_gsm 	    conversion to magnetic GSM coordinates
	/to_ihg 	    conversion to inertial heliographic coordinates

	/heliocentric	    used in conjunction with from_centered_ecliptic and
			    to_centered_ecliptic keywords: sun-centered if /heliocentric
			    is NOT set; earth-centered if /heliocentric SET

	/degrees	    input and output angles are in degrees
	/rectangular	    input and output is in rectangular coordinates

	silent=silent	    suppresses information messages
 INPUTS/OUTPUTS:
	Result		array[2,*] or array[3,*]; type: double
			    output array according to selected /to... keyword
			    if /rectangular is set then the output array will be
			    in rectangular (x,y,z) coordinates; otherwise spherical
			    coordinates (longitude, latitude, and (optional) radial
			    distance is returned
 OPTIONAL OUTPUTS:
	euler_angles=euler_angles
			array[3,*]; type: double
			    Euler angles applied to input coordinates.
	euler_info=euler_info
			scalar; type: string
			    descriptive string describing the transformation
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	CombineRotations, CvSky_Equatorial, CvSky_GSE, CvSky_GSM, CvSky_Galactic
	CvSky_Geographic, CvSky_Heliographic, CvSky_IHG, CvSky_RTN, EulerRotate, InitVar
	IsType, REVERSE, SuperArray, big_eph, destroyvar, jpl_body, who_am_i
 CALLED BY:
	Carrington, CvPrecess, CvSky_GSM, EarthSky3DLoc, EarthTransit3DLoc
	InsituTimeSeries [1], InsituTimeSeries [2], PlotCoronagraph, PlotEarthSkymap
	PlotEloTimeMap, PlotPolarSkymap, RemoteView, RemoteView_BodyLoc
	RemoteView_Display2D, RemoteView_FovTilt, RemoteView_Init_View
	RemoteView_ZEclipticPlane, RotationMeasure, ScEarth, big_eph, big_orbit, cvsmei
	jpl_eph, jpl_test, mpc_eph, mpc_orbit_eph, smei_frm_where, smei_sky
	smei_sky_getmask, smei_zld_model, smei_zld_remove [1], smei_zld_remove [2]
	usno_eph, vu_coronagraph, vu_elotime, vu_extract, vu_linecut, vu_planarcut
	vu_point_source, vu_spherecut, vu_timeseries, vu_vox_drawelatitude
	vu_vox_drawelongitude, vu_vox_draworbit, vu_vox_write
 PROCEDURE:
	For the regular celestial coordinate frames see e.g.
	R. Green, Spherical Astronomy, Cambridge UP, 1985, Section 17.7, p. 430.

	For magnetic RTN,GSE and GSM coordinate frames, see
	    ???

	GSE used for magnetic measurements near Earth
	    x-axis towards Sun, z-axis towards ecliptic North pole
	GSM variation on GSE
	    x-axis towards Sun, z-axis along projection of Earth's magnetic
	    dipole in plane perpendicular  to x-axis. The y-z plane is the
	    same for GSE and GSM.
	RTN used for magnetic field measurements in a heliographic reference
	    frame. x-axis (R-axis) points radially away from the Sun
	    The y-axis (T-axis) is the cross product of solar north (solar
	    rotations axis) and R-axis. The z-axis (N-axis) is the cross product
	    of R and T-axis.
	    For an observer in the solar equator the N-axis points toward solar North.
	    For an observer at Earth x(RTN) = - x(GSE) = -x(GSM), and
	    three magnetic coordinate frames share the same y-z plane)
	IHG used for outer-heliospheric studies. z-axis is toward solar North.
	    x-axis is towards ascending node of solar equator on ecliptic.
 MODIFICATION HISTORY:
	MAR-1997, Paul Hick (UCSD/CASS)
	    adapted from FORTRAN version
	MAR-1998, Paul Hick (UCSD/CASS)
	    now accepts multi-dim arrays
	JAN-2001, Paul Hick (UCSD/CASS)
	    added /rectangular keyword
	SEP-2001, Tamsen Dunn, Paul Hick (UCSD/CASS)
	    added transformations from/to magnetic frames RTN, GSE and GSM
	SEP-2006, Paul Hick (UCSD/CASS)
	    Added fromvectors argument
	    Added from_centered_ecliptic and to_centered_ecliptic keywords
	    Added euler_angles and euler_info keywords
	    Added silent keyword
	    Added underscores to to* and from* keywords
	OCT-2006, Paul Hick (UCSD/CASS)
	    Now accumulates all Euler angles and calls EulerRotate only once
	    to perform the coordinate transformation.
	JUN-2008, Paul Hick (UCSD/CASS)
	    Added /to_ihg and from_ihg=from_ihg keywords.
	DEC-2009, Paul Hick (UCSD/CASS)
	    Bugfix. If fromvectors is used, in combination with more than one
	    of the from_* keywords, routine would abort.
	JUL-2012, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Added from_centered_heliographic and to_centered_heliographic

 NAME:
	CvSky_Equatorial
 PURPOSE:
	Euler angles for Ecliptic --> Equatorial conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	abc = CvSky_Equatorial(UT [, /degrees)
 INPUTS:
	UT	    array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set, all angles are in degrees (default: radians)
 OUTPUTS:
	abc	    array[3,n]; type: double
			Euler angles for converting from
			ecliptic to equatorial coordinates
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	SubArray, SuperArray, TimeGet, ToDegrees
 CALLED BY:
	CvSky, CvSky_Galactic
 PROCEDURE:
	Angle ecliptic-equator as in:
	Spherical Astronomy, R.M. Green, Cambridge UP, p. 220, eq 9.25
 MODIFICATION HISTORY:
	AUG-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CvSky_Galactic
 PURPOSE:
	Euler angles for Ecliptic --> Galactic conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_Galactic, UT, degrees=Degrees
 INPUTS:
	UT	    array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees	if set, all angles are in degrees (default: radians)
 OUTPUTS:
	abc	    array[3,n]; Euler angles for converting from
			ecliptic to heliographic coordinates
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	CombineRotations, CvRotation, CvSky_Equatorial, CvSky_Precess, REVERSE, TimeSet
 CALLED BY:
	CvSky
 PROCEDURE:
	Angle ecliptic-equator as in:
	Spherical Astronomy, R.M. Green, Cambridge UP, p. 41, eq 2.31
 MODIFICATION HISTORY:
	SEP-2003, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CvSky_Geographic
 PURPOSE:
	Euler angles for Ecliptic to Geographic conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_Geographic, UT, degrees=Degrees
 INPUTS:
	UT  array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set all angles are in degrees (default: radians)
 OUTPUTS:
	abc array[3,n]; type: float
	    Euler angles
 INCLUDE:
	@compile_opt.pro		; On error, return to caller
 CALLS: ***
	SubArray, SuperArray, TimeGet, ToDegrees
 CALLED BY:
	CvSky
 PROCEDURE:
 MODIFICATION HISTORY:
	AUG-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CvSky_GSE
 PURPOSE:
	Euler angles for Ecliptic to GSE conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_GSE, UT, degrees=degrees
 INPUTS:
	UT  array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set all angles are in degrees (default: radians)
 OUTPUTS:
	Result	    array[3,n]; type: float
			Euler angles
 INCLUDE:
	@compile_opt.pro		; On error, return to caller
 CALLS: ***
	SubArray, big_eph, jpl_body
 CALLED BY:
	CvSky
 PROCEDURE:
	Geocentric Solar Ecliptic (GSE) coordinates:
	x-axis points from Earth to Sun
	y-axis is in the ecliptic plane opposing orbital motion
	z-axis	points to ecliptic north
 MODIFICATION HISTORY:
	AUG-2002, Paul Hick (UCSD/CASS)
	OCT-2006, Pual Hick (UCSD/CASS; pphick@ucsd.edu)
	    Replaced NewcombSun by big_eph

 NAME:
	CvSky_GSEQ
 PURPOSE:
	Euler angles for Ecliptic to GSEQ conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_GSEQ, UT, degrees=degrees
 INPUTS:
	UT  array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set all angles are in degrees (default: radians)
 OUTPUTS:
	Result	    array[3,n]; type: float
			Euler angles
 INCLUDE:
	@compile_opt.pro		; On error, return to caller
 CALLS: ***
	SubArray, SuperArray, big_eph, jpl_body
 PROCEDURE:
	Geocentric Solar Equatorial (GSEQ) coordinates:
	x-axis points from Earth to Sun
	y-axis is parallel to Sun's equatorial plane pointing
	    east of the Sun
	z-axis is pointing north and completes righthanded
	    coordinate frame

	The Sun's rotation axis lies in the x-z plane.
 MODIFICATION HISTORY:
	OCT-2006, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CvSky_GSM
 PURPOSE:
	Euler angles for Ecliptic to GSM conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_GSM, UT, degrees=degrees
 INPUTS:
	UT  array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set all angles are in degrees (default: radians)
 OUTPUTS:
	Result	array[3,n]; type: float
	    Euler angles
 INCLUDE:
	@compile_opt.pro			    ; On error, return to caller
 CALLS: ***
	CvSky, SubArray, SuperArray, TimeGet, ToDegrees, ToRadians, big_eph, jpl_body
 CALLED BY:
	CvSky
 PROCEDURE:
	Geocentric Solar Magnetospheric (GSM) coordinates
	x-axis points from Earth to Sun
	z-axis is the northern magnetic pole, projected in plane perp to x-axis.
	The difference between the GSM system and the GSE
	and GSEQ is a rotation about the X-axis.
 MODIFICATION HISTORY:
	AUG-2002, Paul Hick (UCSD/CASS)
	JUN-2007, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Bugfix. The conversion of UT to years since 2000 somehow
	    lost the subtraction of 2000.

 NAME:
	CvSky_Heliographic
 PURPOSE:
	Euler angles for Ecliptic to Heliographic conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_Heliographic, UT, degrees=degrees, longitude=longitude
 INPUTS:
	UT	array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	longitude   array[n] or scalar; type: float; default: 0
		    heliographic longitude(s). See PROCEDURE.
	/degrees    if set all angles are in degrees (default: radians)
 OUTPUTS:
	abc	array[3,n]; type: float
		Euler angles for rotation from ecliptic to heliographic
		coordinate frame
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	AngleRange, IsType, SubArray, SuperArray, TimeGet, TimeUnit, ToDegrees
 CALLED BY:
	CvSky, vu_solardisk
 SEE ALSO:
	CvSky_IHG
 PROCEDURE:
	The ecliptic longitude for the ascending node and the inclination of
	equator to ecliptic are from R. Green, "Spherical astronomy", p. 431

	If keyword 'longitude' is specified than the Euler angles refer
	to a rotation from an ecliptic reference frame to a
	heliographic reference frame with longitude measured from the
	heliographic meridian through 'longitude', instead of the
	heliographic prime meridian (i.e. heliographic longitude zero).
	This is useful, for instance, to set up 'earth-centered'
	heliographic coordinates with heliographic longitude measured
	from the heliographic longitude of Earth.
 MODIFICATION HISTORY:
	AUG-2002, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CvSky_IHG
 PURPOSE:
	Euler angles for Ecliptic to IHG conversion
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_IHG, UT, degrees=degrees
 INPUTS:
	UT	array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set all angles are in degrees (default: radians)
 OUTPUTS:
	abc	array[3,n]; type: float
		Euler angles
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	SubArray, SuperArray, TimeGet, TimeUnit, ToDegrees
 CALLED BY:
	CvSky
 SEE ALSO:
	CvSky_Heliographic
 PROCEDURE:
	The IHG z-axis is along the solar rotation axis (solar north).
	The x-axis is toward the ascending node of the solar equator
	on the ecliptic. See
	http://nssdcftp.gsfc.nasa.gov/miscellaneous/documents/b46547.txt
	and Burlaga, "MHD Processes in the Outer Heliosphere",
	    Space Sci. Rev. 39, 255-316, 1984.
	Note that the nssdc website says:
	"The X(IHG) axis drifts slowly with time, approximately one
	degree per 72 years", while the Burlaga paper says (p. 260)
	".. we shall take the X(IHG) axis along the direction of the
	ascending node in 1900". I.e. the Burlaga paper seems to want
	the X(IHG) axis fixed at epoch 1900.
	Here we follow the description of the website.
	The ecliptic longitude for the ascending node and the
	inclination of equator to ecliptic are from
	R. Green, "Spherical astronomy", p. 431
 MODIFICATION HISTORY:
	JUN-2008, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CvSky_Precess
 PURPOSE:
	Euler angles for precesion of equatorial coordinates from epoch UT to J2000
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	abc = CvSky_Precess(UT [, /degrees)
 INPUTS:
	UT	    array[n]; type: time structure
 OPTIONAL INPUT PARAMETERS:
	/degrees	if set, all angles are in degrees (default: radians)
 OUTPUTS:
	abc	    array[3,n]; Euler angles for precession from epoch UT to J2000
 INCLUDE:
	@compile_opt.pro	; On error, return to caller
 CALLS: ***
	SubArray, SuperArray, TimeGet, ToDegrees
 CALLED BY:
	CvPrecess, CvSky_Galactic
 PROCEDURE:
	Precession angles from:
	Spherical Astronomy, R.M. Green, Cambridge UP, p. 219, eq 9.23
 MODIFICATION HISTORY:
	DEC-2003, Paul Hick (UCSD/CASS; pphick@ucsd.edu)

 NAME:
	CvSky_RTN
 PURPOSE:
	Euler angles for Heliographic to RTN conversion at Earth
 CATEGORY:
	smei/gen/idl/ephem
 CALLING SEQUENCE:
	FUNCTION CvSky_RTN, UT_or_LOC, degrees=degrees
 INPUTS:
	UT_or_LOC	array[3,n]; type: float
			    heliocentric locations in heliographic
			    coordinates (heliographic longitude, latitude and
			    distance)
			array[n]; type: time structure
			    UT times; in this case the heliocentric locations
			    is assumed to be at Earth at the specified times
 OPTIONAL INPUT PARAMETERS:
	/degrees    if set all angles are in degrees (default: radians)
 OUTPUTS:
	Result	    array[3,n]; type: float
			Euler angles to rotate from heliographic
			coordinates to RTN coordinates
 INCLUDE:
	@compile_opt.pro	    ; On error, return to caller
 CALLS: ***
	IsTime, SubArray, big_eph, jpl_body
 CALLED BY:
	CvSky, RotationMeasure
 PROCEDURE:
	RTN (Radial, Tangential, Normal) coordinates at point P:
	x-axis = radial direction
	y-axis = in tangent plane, parallel to solar equator
	z-axis = in tangent plane, pointing toward the solar north pole
 MODIFICATION HISTORY:
	AUG-2002, Paul Hick (UCSD/CASS)
	OCT-2006, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
	    Added option to directly enter heliocentric locations
	    in addition to always using Earth's location.