ELLPRO-Performs an ellipse fitting galaxy profile using simple intensity analysis

Description:

Performs an ellipse fitting galaxy profile using simple intensity analysis. The position of the centre of the galaxy (and a number of other parameters) may be specified interactively (using cursor or keyboard) or the location within the image of several galaxies may be specified using an ASCII text file.

A number of options allow the user to determine criteria for; when profiling should end, whether an ARD file is to be used to mask out bad areas of the image, whether the initial galaxy centre value is to be fixed throughout profiling and also whether or not the initial galaxy centre co-ordinates provided by the user may be refined by the application before the first profile is generated.

The position of the centre of the galaxy in question may be input interactively, MODE=TRUE), or (if there are many galaxies to be considered) may be read in from a text file (MODE=FALSE). In addition, when in MODE=TRUE the galaxy can be identified using a cursor (CURSOR=TRUE) as opposed to a keyboard entry of its co-ordinates.

Usage:

ELLPRO MODE BACK SIGMA PSIZE ZEROP ARDFIL DEVICE OUT (OUTCAT)
     AUTOL AUTOLT FRZORI [CURSOR] [IN] [ORIGIN] (FAST)
     (FINE) [RLIM] (LIM1) (LIM2) (LIM3) (FRACT) [SAME]
     [AGAIN] [INFILE) [IMGDEV] (COLOUR) (ANGCON) (ANGOFF)

Parameters:

AGAIN=_LOGICAL (Read)

Allows the user to elect to repeat the profiling operation on the current input image.

ANGCON=_LOGICAL (Read)

Angle rotation convention. Defines if clockwise or anticlockwise is considered positive. TRUE=Clockwise.

ANGOFF=_REAL (Read)

Angular offset for position angles generated. Units degrees.

ARDFIL=_CHAR (Read)

The name of an ARD file to be used to mask out regions of the image that are not to be used.

AUTOL=_LOGICAL (Read)

If true, then the application attempts to find a better initial estimate of the galaxy centre. See also the AUTOLT parameter for further control of this, and contrast the FRZORI parameter.

AUTOLT=_LOGICAL (Read)

Controls the method used when improving the estimate of the galaxy centre (see parameter AUTOL). If autolt=true, the application refines the initial galaxy centre by taking the centroid of the points in a small region around the given location. If autolt=false, it uses an alternative weighted-mean method.

BACK=_REAL (Read)

The background count value for the image. Units counts.

COLOUR = _INTEGER (Given)

Colour of the pen used to mark galaxy centres.

CURSOR=_LOGICAL (Read)

Whether the galaxy locations are to be identified using the graphics cursor or the keyboard. True=cursor. False=keyboard.

DEVICE=_DEVICE (Read)

Name of the graphics device on which the results graph should be displayed.

FAST=_LOGICAL (Read)

Is the faster method of profiling to be used? Default value is true. The slower version should yield better values at low radii values since surface interpolation (rather than bi-linear) is used. The surface generated by the slow method to model the galaxy near its centre is a 8x8 bi-cubic spline, so considerable calculation is involved.

FINE=_REAL (Read)

A factor modifying the default separation of ellipses profiled. The default value is 1. Decreasing this value increases the number of profiles generated for a given object. Increasing this value above 2.0 is not recommended.

FRACT=_REAL (Read)

The minimum fraction of the points round the ellipse for which no value was available due to either image pixels set to the bad value or parts of the ellipse being beyond the bounds of the image. If the fraction of points available for a given ellipse drops below this value the results for that radius are not kept.

FRZORI=_LOGICAL (Read)

If FRZORI is true, then the initial galaxy position, after any initial refinement if the AUTOL parameter is true, will be frozen for the rest of the calculation. If FRZORI is false, then the initial estimate will be allowed to drift if that improves an ellipse fit.

IMGDEV=_DEVICE (Read)

Name of the graphics device displaying an image.

INFILE=_CHAR (Read)

Name of a text file containing the co-ordinates of galaxies to be profiled. (Only used in file mode i.e. MODE=FALSE) Co-ordinates are in the Current coordinate system of the WCS component of IN.

IN=_NDF (Read)

The name of the source NDF data structure/file.

LIM1=_REAL (Read)

The maximum ratio that is permitted between the average mean count value of the two preceeding radii profiled and that of the current radius. If this value is exceeded, the profiling operation stops.

LIM2=_REAL (Read)

The lower limit for mean profile count value (above sky). If the mean count value for the current profile drops below this value the profiling operation stops. Units are standard deviations.

LIM3=_REAL (Read)

The distance from the galaxy origin at which the profile is assumed to maintain a constant position angle, origin and ellipticity. At radii beyond these, parameters are no longer modified. The position angle, origin and ellipticity are not frozen if a value of zero or less than zero is suggested. Units are pixels

MINMOD=_INTEGER (Read)

Which type of ellipse-residual minimisation is to be used.

The type of residual to be calculated is specified as 0, 1 or 2. This also controls which type of statistic is returned in the final column of the ELLPRO output file. It's not completely clear what is the best type of residual to use. The original one - a weighted standard error, selected by giving this parameter the option$\sim$0 - is rational, but not obviously ideal. I've added here the range and the squared-differences as alternatives, selectable by options$\sim$1 and$\sim$2 respectively.

I don't really recommend you play with this unless you wish to experiment. If this parameter makes much of a difference, the ESP maintainer would be interested to hear about it.

MODE=_LOGICAL (Read)

Whether the application is to run in file input mode or interactively. Interactive MODE=TRUE. File mode=FALSE.

ORIGIN=_REAL (Read)

Image co-ordinates for the origin point to be used. Co-ordinates are in the Current co-ordinate system of the WCS component of IN.

OUT=_CHAR (Read)

File name for the output text file containing the profile data.

OUTCAT=_CHAR (Read)

File name for an output file which is written using the CAT library. See SUN/181. The type of catalogue which is written depends on the file extension to the filename presented here. A file ending .txt will be written as a STL (Small Text List) file, and one ending .fits will be written as a FITS file.

PSIZE=_REAL (Read)

The size of each pixel in arc seconds. If the image contains a SKY co-ordinate frame this value will be determined automatically.

RLIM=_REAL (Read)

Radius at which the profiling will be stopped. Units pixels.

SAME=_LOGICAL (Read)

Is the results graph to be displayed on the device currently displaying the input image? Only valid if CURSOR is true. If SAME is set to true then the user is prompted to identify the quadrant of the input device in which graph will be displayed.

SIGMA=_REAL (Read)

The standard deviation of the background value. Units counts.

ZEROP=_REAL (Read)

Zero point of the scale for surface brightness plots. Units magnitudes per arc seconds.

Examples:

ellpro mode=true back=6200 sigma=390

zerop=27.5 ardfil=$\wedge$ardfile.dat device=xwindows
     out=elp1.dat autol=true frzori=false cursor=false
     in=p2 rlim=10 origin="12:36:53.42 62:12:21.8"

Performs profiling on an object positioned at the co-ordinates indicated on image P2; the Current co-ordinate system of P2 is in the SKY domain. Pixel size in arcseconds will be determined automatically from the SKY co-ordinates. The profile determined will be output to a graphical display on device XWINDOWS and to text file ELP1.DAT. The galaxy centre provided will be refined by the application and during profiling the galaxy centre will be allowed to change. The profiling will be stopped at a radius of 10 pixels.

ellpro mode=true back=6200 sigma=390 psize=1. zerop=27.5

ardfil=$\wedge$ardfile.dat device=xwindows out=elp1.dat
     autol=false frzori=true cursor=true

Performs profiling on a galaxy identified using a cursor/mouse and the most recently displayed image. The ARD area definition contained in the file ARDFILE.DAT is used to mask out bad parts of the image. The galaxy centre identified by the user is not refined by the software and is not allowed to change during profiling. The galaxy location is defined using a cursor/mouse on the most recently displayed image.

ellpro mode=false back=760 sigma=12 psize=0.44 zerop=27.5

ardfil=$\wedge$arddef.dat in=p2 infile=p2log.dat
     out=output.dat autol=true frzori=false

The appliication reads the object locations in file P2LOG.DAT (in the Current co-ordinates of P2) and performs profiling on those locations on image P2. The profiling output is displayed on the text screen and is also placed in file OUTPUT.DAT.

Notes:

Parameters surrounded by curved brackets may only be modified via the command line.