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Last modified: Wed Aug 13 22:06:15 2008.
NAME:
FINDCLIP
DESCRIPTION:
This function estimates how to scale a first moment map of a data
cube such that regions of interest will show a maximal velocity
range. The idea is to calculate lower and upper bounds to the
velocities in the first moment map. Pixels outside these boundaries
should be set to these boundaries, effectively compressing the range of
values to display on a screen. This is accomplished by finding whch
range of velocities cover a set of pixels in a first moment map
whose values in the zeroth moment map occupy most of the total flux
in that map. This is meant to mimic what the IDL astronomy routine
SIGRANGE does for a single image.
CALLING SEQUENCE:
result=FINDCLIP(inmom0, inmom1, [FRACTION=fraction, /NOZERO])
INPUTS:
inmom0: A 2d image giving the zeroth moment of some data cube
inmom1: A 2d image giving the first moment of the same data cube
KEYWORD PARAMETERS:
FRACTION: Set this keyword to be what fraction of the mom0 map flux
is contained within pixels which fall inbetween the output
velocity boundaries in the mom1 map. If not set, 0.9 is used.
NOZERO: If set, treat zeroes in the input maps as missing data.
OUTPUT:
A 2 element vector giving two velocities. The pixels falling
between the range of these two values in inmom1 have values in
inmom0 which together comprise 0.9 (or FRACTION) of the total flux
in inmom0.
MODIFICATION HISTORY:
August 13, 2008: Written by Chris Beaumont
(See findclip.pro)
NAME: GCROT PURPOSE: This function computes, as a function of galactic coordinates, the angle between a vector pointing towards the galactic north pole and a vector pointing towards the North Celestial Pole. This can be used to commonly orient images aligned to ecliptic and galactic coordinate systems. CALLING SEQUENCE: result=GCROT(L,B,/DEGREE,/RADIAN) INPUTS: L: Galactic longitude. Radians are assumed unless /DEGREE is set. B: Galactic latitude. Radians are assumed unless /DEGREE is set. KEYWORD PARAMETERS: /DEGREE: If set, the input and output are given in degrees. OUTPUT: The clockwise rotation that aligns the galactic north pole with the NCP (in J2000 coordinates). In radians by default. RESTRICTIONS: This has not been tested for accuracy higher than roughly .5 degrees. I wouldn't use this to determine the orientation of spectra slits or other high precision tasks without testing first. MODIFICATION HISTORY: Written by: Chris Beaumont, May 2008. June 2008 Chris Beaumont- Added /degree keyword. cnb
(See gcrot.pro)
NAME: KDIST PURPOSE: This function calculates the near and far kinematic distances for a given galactic longitude and radial velocity. The calculation uses the Galactic rotaion model of Brand and Blitz 1993, A&A, 275 : 67. CALLING SEQUENCE: result=KDIST( Latitude, Velocity, [/RADIANS]) INPUTS: Latitude: Galactic Latitude. Currently must be in the range [-180, 180] in degrees. Velocity: Radial velocity in km/s KEYWORD PARAMETERS: /RADIANS: If set, input Latitude is in radians OUTPUT: The two element vector [near_distance, far_distance] in kpc. RESTRICTIONS: Currently only computes distances for objects in the inner galaxy. MODIFICATION HISTORY: Written by: Chris Beaumont, June 2008. June 23, 2008: Changed name from kinematic_distance to kdist. cnb June 23, 2008: Fixed bug in modding l with 2 pi. cnb July 17, 2008: Removed degrees keyword. Added radians. cnb July 17, 2008: Changed things so that, if l is a variable, it isn't modified
(See kdist.pro)
NAME:
KDISTERR
DESCRIPTION:
This function calculates the two kinematic distances, with errors,
for a given object whose velocity is known to some precision.
CALLING SEQUENCE:
result=KDISTERR( l, vlow, vhigh, [/RADIANS, /SILENT])
INPUTS:
l: The galactic longitude of the source given in degrees (or
radians, if /RADIANS is set)
vlow: The lower bound for the radial velocity estimate, in km/s
vhigh: The uppper bound for the radial velocity estimate, in km/s
OPTIONAL KEYWORDS:
RADIANS: If set, l is given in radians
SILENT: If set, textual summary of the results are suppressed
OUTPUT:
A 4 element vector. The first and third elements give the near and
far kinematic distances in kpc, while the second and fourth give
error estimates.
RESTRICTIONS:
This only works for objects with latitudes between 270 degrees and
90 degrees, for which there are two possible kinematic distances
FUNCTIONS CALLED:
kdist
MODIFICATION HISTORY:
June 2008: Written by Chris Beaumont
(See kdisterr.pro)
NAME:
NEXTAST
PURPOSE:
This function returns a structure of astrometry parameters parsed
from a FITS header. It is meant to mimic the IDL Astronomy User's
Library routine 'EXTAST', but is generalized to handing
N-dimensional data files (e.g. spectral data cubes). Note, however,
that EXTAST handles a wider variety of astrometry parameters and,
I'm sure, is much more robust for 2D FITS files
CALLING SEQUENCE:
result=EXTAST(header)
INPUTS:
header: A string array containing a fits header (ie, the output
from mrdfits)
OUTPUTS;
An anonymous structure with the following tags:
.NAXIS- the number of axes in the file
.SZ - An NAXIS element array containing NAXIS1...NAXIS[N]
.CD - An NAXIS x NAXIS array holding the CD/cdelt keywords.
CD[i,j]=CD[I]_J. If the header uses CDELT keywords
instead, they are converted to matrix form (CDELT1 =
CD1_1)
.CRPIX - An NAXIS element array containing the CRPIX keywords
.CRVAL - An NAXIS element array containing the CRVAl keywords
.CTYPE - An NAXIS element array containing the CTYPE keywords
RESTRICTIONS:
Error checking is limited. This was developed and tested for fits
files using cdelt or cdi_j keywords, with no distortion or other
fancy features.
FUNCTIONS CALLED:
SXPAR
CATEGORY:
FITS manipulation, Astrometry
MODIFICATION HISTORY:
July 27, 2008: Written by Chris Beaumont
(See nextast.pro)
NAME:
NICER
DESCRIPTION:
This function estimates the reddening to a star based on its JHK
colors. Based on the NICER algorithm (Lombardi and Alves, 2001).
CALLING SEQUENCE:
result=NICER(j,dj,h,dh,k,dk)
INPUTS:
J,H,K: scalar or n-element vectors of a set of J,H,K magnitudes of a
star. If any data are missing, insert fake data and see next
sentnce.
dH,dJ,dK: scalar or n-element vectors of the errors in the JHK
colors. If any JHK data are unknown, insert fake data for
those entries, and make the corresponding error entry
extremely large. This will cause the algorithm to ignore
the fake data point during fitting.
OUTPUT:
A 2 x n element array giving nth row gives the magnitudes of
visual extinction, with associated error, estimated for star n.
CATEGORIES:
Photometry, Interstellar extinction
MODIFICATION HISTORY:
July 2008: Written by Chris Beaumont
(See nicer.pro)
NAME:
POSTAGESTAMP
DESCRIPTION:
This function extracts a subregion from a 2 or 3-dimensional FITS
image. It uses a nearest-neighbor regridding scheme.
CALLING SEQUENCE:
result=POSTAGESTAMP(im, head, cen, wid, scale, [/NAN])
INPUTS:
IM: A 2- or 3-dimensional image array
HEAD: The FITS header corresponding to IM (as is generated by
MRDFITS, for example)
CEN: A 2 or 3 element array giving the center of the desired
subfield in 'real sky units' (i.e. whatever real sky units are
assumed within the CRVAL keywords of HEAD)
WID: A 2 or 3 element array giving the size of the extracted
subfield in 'real sky units' (see note for CEN)
SCALE: A 2 or 3 element array giving the size of the output pixels
in real sky units (whatever real sky units are assumed in
the CD or CDELT keywords of HEAD)
KEYWORD PARAMETERS:
NAN: If set and nonzero, regions of the subimage which lie outside
the boundaries of the input image are output as NaN. Otherwise,
they are output as zero.
EXAMPLE:
Given im and head, extract a .25 x .25 degree field centered at
(a,d)=(10.,20.) where each pixel is .002 degrees
result=postagestamp(in,head,[10.,20.],[.25,.25],.[.002,.002])
Repeat, but this time preserve the convention that RA increases to
the left in sky images:
result=postagestamp(in,head,[10.,20.],[.25,.25],[-.002,.002])
SIDE EFFECTS:
The coordinates of CEN will always be the exact center of the
output image, and the pixels will always be exactly the size given
by scale. However, the output images have an odd number of pixels
along each axis, and thus may be a pixel or two different from the
size requested by WID.
This function uses SKY2PIX, which provides rather limited
astrometry capabilities (e.g. no corrections for field curvature or
other higher order distortion terms).
FUNCTIONS CALLED:
NEXTAST, SKY2PIX, SXPAR
CATEGORY:
FITS image manipulation, astrometry
MODIFICATION HISTORY:
August 9, 2008: Written by Chris Beaumont
(See postagestamp.pro)
NAME:
SKY2PIX
PURPOSE:
This function translates between 'real' coordinates (eg, ra dec) to
pixel coordinates in a fits file. Pixel co-ordinates are given as
zero-indexed values (IDL convention) as opposed to 1-indexed (FITS
convention). This was designed as a substute for ad2xy for
multi-dimensional fits files (eg spectral data cubes, where extast
chokes)
CALLING SEQUENCE:
result=sky2pix(header,coords,/backwards)
INPUTS:
header: A string array containing a fits header (eg, from mrdfits)
Coords: An n by m array containing the n-dimensional coordinates of
m datapoints. These are 'real sky' coordinates, unless the
backwards keyword is set. If some of the higher dimensional
coordinates are not needed for conversion, they may be
omitted. If this is the case, however, only the first n
dimensions will be given on output.
OPTIONAL KEYWORDS:
backwards: coords are given in pixel coordinates, and the output is
given in sky coordinates
OUTPUT:
result: An array contining the pixel coordinates of the real coordinates
given by coords. This array is the same size as coords.
result [i,j] contains the coordinate component of the jth data point
along the ith pixel dimension.
result[*,j] contains the coordinate of the jth data point.
EXAMPLES:
find the pixel location of (ra,dec,vel)=(5,6,7) in header h
IDL> result=sky2pix(h,[5,6,7])
find the pixel location of (ra,dec)=(5,6) in a data cube with
header h, but whose third dimension (velocity) is not needed for
the converstion
IDL> result=sky2pix(h,[5,6])
Note: result has only 2 dimensions, corresponding to the images
x,y coords. The Z coordinate (velocity) is not used or returned
RESTRICTIONS:
The program relies upon NEXTAST, and thus isn't robust to unusual
FITS files. This is meant to correctly convert coordinates using
headers with crpix,crval,and cdelt or cd. If the header has extra
information (distortion terms, projection terms) necessary for
proper astrometry calculations, sky2pix will not give correct
answers.
FUNCTIONS CALLED:
NEXTAST
CATEGORY:
astrometry, coordinate conversion
MODIFICATION HISTORY:
July 27 2008: Written by Chris Beaumont
(See sky2pix.pro)