ELLFOU

Ellipse fitting galaxy profiles using contour analysis

Description:

Performs the calculations to fit galaxy profiles using ellipses. The method used involves fitting an ellipse to the shape of the isophote contour.

The output includes the ellipse parameters, the azimuthally-averaged intensity around them, and the Fourier descriptors. The position of the centre of the galaxy (and a number of other parameters) must be specified interactively (using cursor or keyboard) by the user.

If MODE is false, a list containing the location of galaxies within an image, is obtained from an ASCII file. profiles are generated for all these objects.

If MODE is true, a value for the parameter CURSOR is required. If CURSOR is true, then a cursor/mouse is used (in conjunction with the most recent image displayed) to determine information such as proposed galaxy centre and the largest ellipse radius to be used. If CURSOR is false, a keyboard is used for all input required by the application.

Usage:

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

Parameters:

Allows the user to elect to repeat the profiling operation on the current input image. Profiling is repeated if AGAIN=TRUE.
Position angle convention. TRUE=clockwise positive
Positive angle offset. Units degrees.
The name of an ARD file to be used to mask out regions of the image that are not to be used.
Is a better estimate of the galaxy centre position to be obtained? If AUTOL=FALSE the user estimate is employed, otherwise the application examines the area of the image near the user defined co-ordinates for a better estimate.
The type of centroiding method used. N=centroid, Y=weighted mean
The background count value for the image. Units counts.
Colour of the pen used to mark the position of the galaxy centre.
Whether the galaxy locations are to be identified using the graphics cursor or the keyboard. Cursor/mouse is used if CURSOR=TRUE.
The name of the graphics device on which the graph of results should be displayed.
Fraction of pixels that must be present for a fit to be okay.
A factor modifying the default separation of isophotal separation of the pixels used to create ellipses. The default value is 1. Decreasing this value increases the number of profiles generated for a given object. Must be issued from the command line.
Allows the origin given (or the values determined via AUTOL) to remain unchanged throughout the current profiling operation. The origin is free to move if FRZORI=FALSE.
Name of the graphics device displaying the current image.
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 co-ordinate frame of the WCS component of IN. The file may also contain a third column containing the background count value. If this is found to be absent the global background count value (BACK) is substituted.
The name of the source NDF data structure/file.
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 ratio is exceeded, the profiling operation stops. Must be issued from the command line.
The lower limit for mean profile count value. If the mean count value for the current profile drops below this value the profiling operation stops. Must be issued from the command line.
Whether the application is to run in file input mode or interactively. Interactive MODE=TRUE. File mode=FALSE.
Image co-ordinates for the galaxy origin point to be used. To be given in the Current coordinate system of the source NDF.
File name for the output text file containing the profile data.
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.
The size of each pixel in arc seconds. If the image contains a SKY co-ordinate frame this value will be determined automatically.
Radius at which the profiling will be stopped. Units pixels.
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.
The standard deviation of the background count value. Units counts.
Zero point of the scale for surface brightness plots. Units magnitudes per arc seconds.

Examples:

ellfou mode=true back=6200. sigma=390. psize=1.
zerop=27.5 ardfil=^ardfile.dat device=xwindow out=elf autol=true frzori=true cursor=true same=true

Profiles are obtained for the image co-ordinates determined using the cursor/mouse on the DATA image currently displayed on device XWINDOW. The background count value of that image is 6200 with an associated standard deviation of 390. The magnitude scale assumed has a zero point of 27.5, all profiles will be output to text file ELF, the final results will also be plotted on the XWINDOW device and the galaxy centre co-ordinates are allowed to vary.

ellfou mode=true back=1267. sigma=45. psize=2.
zerop=26.2 ardfil=^ardfile.dat device=xwindow out=elf2 autol=true frzori=true cursor=true same=false imgdev=x2windows

Profiles are obtained for the current data image on device XWINDOW. The results are output onto device X2WINDOWS. An ARD file definition in ARDFILE.DAT is used to identify parts of the image that may be used in the profiling operation. An attempt will be made to improve the co-ordinates indicated via the cursor/mouse but the galaxy centre co-ordinates will not be allowed to vary from one profile to the next.

ellfou mode=true back=6200 sigma=390. zerop=27.5
ardfil=^ardfile.dat out=elf autol=true frzori=true cursor=false in=p2 origin="12:36:53.42 62:12:21.8" rlim=10. imgdev=x2windows

Profiles for the object at the co-ordinates indicated on image P2 are obtained out to a radius of 10 pixels. The Current co-ordinate frame of P2 is in the ’SKY’ domain. Pixel size in arcseconds is determined automatically from the SKY co-ordinates. The results are output to device X2WINDOWS and to a file text file ELF. The background count is 6200 with an associated standard deviation of 390.

ellfou mode=false infile=coords ardfil=^ardfile.dat in=jet
frzori=false back=3713 sigma=23 rlim=20 psize=0.5 zerop=26.2 autol=false

The program is operated in file mode where co-ordinates of the galaxies to be profiled are read from file COORDS. An ARD file ARDFILE.DAT is used to identify parts of the image that can be used. The global value for the background count value is input in case the COORDS file does not contain a third column with local background values in. The image used as the source is JET. During profiling the galaxy centre is allowed to vary from that originally provided in the file. The profiling operation ceases if the ellipse radius reaches 20 pixels.

Notes:

The parameters surrounded by curved brackets may only be changed from the command line.