MAKECLUMPS

Create simulated data containing clumps and noise

Description:

This application creates a new 1-, 2- or 3-dimensional NDF containing a collection of clumps with background noise. It also creates a catalogue containing the clump parameters.

The clumps profiles are Gaussian, with elliptical isophotes. The values of each parameter defining the clump shape can be either fixed at a constant value or selected from a given probability distribution. The clump positions can be distributed randomly, or may be on a regular grid (see parameter GRID).

Usage:

makeclumps out outcat

Parameters:

ANGLE( 2 ) = _REAL (Read)
Defines the distribution from which the spatial position angle of the major axis of the elliptical clump is chosen. Values should be supplied in units of degrees. See parameter PARDIST for additional information. Note, angles are always taken from a uniform distribution, irrespective of the setting of PARDIST. [current value]
BEAMFWHM = _REAL (Read)
The spatial FHWM (Full Width at Half Max) of the instrumental beam, in pixels. The generated clumps are smoothed with a Gaussian beam of this FWHM, before noise is added. No spatial smoothing is performed if BEAMFWHM is zero. See also parameter PRECAT. [current value]
DECONV = _LOGICAL (Read)
If TRUE, the clump properties stored in the output catalogue will be modified to take account of the smoothing caused by the instrumental beam width. Note, if parameter PRECAT is TRUE, then this deconvolution has no effect since no smoothing has been applied to the clumps at the time when the catalogue is created. [TRUE]
FWHM1( 2 ) = _REAL (Read)
Defines the distribution from which the FWHM (Full Width at Half Max) for pixel axis 1 of each clump is chosen. Values should be supplied in units of pixel. See parameter PARDIST for additional information. [current value]
FWHM2( 2 ) = _REAL (Read)
Defines the distribution from which the FWHM (Full Width at Half Max) for pixel axis 2 of each clump is chosen. Values should be supplied in units of pixel. See parameter PARDIST for additional information. [current value]
FWHM3( 2 ) = _REAL (Read)
Defines the distribution from which the FWHM (Full Width at Half Max) for pixel axis 3 of each clump is chosen. Values should be supplied in units of pixel. See parameter PARDIST for additional information. [current value]
GRID = _INTEGER (Read)
If null (!), the clump centres are distributed randomly over the array. If not null, the clump centres are positioned on a regular grid with dimensions specified by parameter NCLUMPS. The grid occupies the entire output array, excluding a border of width equal to the integer value supplied for parameter GRID (in pixels). [!]
LBND() = _INTEGER (Read)
The lower pixel bounds of the output NDF. The number of values supplied (1, 2 or 3) defines the number of pixel axes in the output NDF (an error is reported if the number of values supplied for LBND and UBND differ). If an NDF is supplied for parameter LIKE, the suggested defaults for this parameter will be the lower pixel bounds of the supplied NDF.
LIKE = NDF (Read)
An NDF from which to inherited WCS information. If a null (!) value is supplied, the output catalogue will hold values in pixel coordinates, and there will be no WCS in any of the output NDFs. [!]
MODEL = NDF (Write)
The NDF to receive the simulated data, excluding noise. A CUPID extension is added to this NDF, containing information about each clump in the same format as produced by the FINDCLUMPS command. This includes an NDF holding an of the individual clump.
NCLUMP() = _INTEGER (Read)
The number of clumps to create. If parameter GRID is null (!), a single value should be supplied, and the specified number of clumps are positioned randomly over the output array. If parameter GRID is not null, the number of values supplied should match the number of pixel axes in the output array, and each value is then the number of clumps along the corresponding pixel axis. Note, any clumps that touch an edge of the aray will be excluded from the output array.
OUT = NDF (Write)
The NDF to receive the simulated data, including instrumental blurring and noise.
OUTCAT = FILENAME (Write)
The output catalogue in which to store the clump parameters. There will be one row per clump, with the following columns:

  • Peak1: The position of the clump peak value on axis 1.

  • Peak2: The position of the clump peak value on axis 2.

  • Peak3: The position of the clump peak value on axis 3.

  • Cen1: The position of the clump centroid on axis 1.

  • Cen2: The position of the clump centroid on axis 2.

  • Cen3: The position of the clump centroid on axis 3.

  • Size1: The size of the clump along pixel axis 1.

  • Size2: The size of the clump along pixel axis 2.

  • Size3: The size of the clump along pixel axis 3.

  • Sum: The total data sum in the clump.

  • Peak: The peak value in the clump.

  • Volume: The total number of pixels falling within the clump.

There is also an optional column called " Shape" containing an STC-S description of the spatial coverage of each clump. See parameter SHAPE.

The coordinate system used to describe the peak and centroid positions is determined by the value supplied for parameter LIKE. If LIKE is null (!), then positions are specified in the pixel coordinate system. In addition, the clump sizes are specified in units of pixels, and the clump volume is specified in units of cubic pixels (square pixels for 2D data). If an NDF is supplied for LIKE, then positions are specified in the current coordinate system of the specified NDF. In addition, the clump sizes and volumes are specified in WCS units. Note, the sizes are still measured parallel to the pixel axes, but are recorded in WCS units rather than pixel units. Celestial coordinate positions are units of degrees, sizes are in units are arc-seconds, and areas in square arc-seconds. Spectral coordinates are in the units displayed by the KAPPA command " ndftrace" .

If the data has less than 3 pixel axes, then the columns describing the missing axes will not be present in the catalogue.

The catalogue inherits any WCS information from the NDF supplied for parameter LIKE.

The " size" of the clump on an axis is the RMS deviation of each pixel centre from the clump centroid, where each pixel is weighted by the correspinding pixel data value. This excludes the instrumental smoothing specified by BEAMFWHM and VELFWHM.

The KAPPA command " listshow" can be used to draw markers at the central positions of the clumps described in a catalogue. For instance, the command " listshow fred plot=mark" will draw markers identifying the positions of the clumps described in file fred.FIT, overlaying the markers on top of the currently displayed image. Specifying " plot=STCS" instead of " plot=mark" will cause the spatial outline of the clump to be drawn if it is present in the catalogue (see parameter SHAPE).

PARDIST = LITERAL (Read)
The shape of the distribution from which clump parameter values are chosen. Can be " Normal" , " Uniform" or " Poisson" . The distribution for each clump parameter is specified by its own ADAM parameter containing two values; the mean and the width of the distribution. If PARDIST is " Normal" , the width is the standard deviation. If PARDIST is " Uniform" , the width is half the range between the maximum and minimum parameter values. In either of these two cases, if a width of zero is supplied, the relevant parameter is given a constant value equal to the specified mean. If PARDIST is " Poisson" , the width is ignored. [current value]
PEAK( 2 ) = _REAL (Read)
Defines the distribution from which the peak value (above the local background) of each clump is chosen. See parameter PARDIST for additional information. [current value]
PRECAT = _LOGICAL (Read)
If FALSE, the output catalogue is created from the clumps after the instrumental smoothing specified by parameters BEAMFWHM and VELFWHM has been applied. If TRUE, the catalogue is created from the data before the instrumental smoothing is applied (in which case parameter DECONV has no effect). [FALSE]
RMS = _REAL (Read)
The RMS (Gaussian) noise to be added to the output data. [current value]
SHAPE = LITERAL (Read)
Specifies the shape that should be used to describe the spatial coverage of each clump in the output catalogue. It can be set to any of the strings described below. If it is set to " None" , the spatial shape of each clump is not recorded in the output catalogue. Otherwise, the catalogue will have an extra column named " Shape" holding an STC-S description of the spatial coverage of each clump. " STC-S" is a textual format developed by the IVOA for describing regions within a WCS - see http://www.ivoa.net/Documents/latest/STC-S.html for details. These STC-S desriptions can be displayed by the KAPPA:LISTSHOW command, or using GAIA. Since STC-S cannot describe regions within a pixel array, it is necessary to provide an NDF to define the WCS (using parameter LIKE) if using this option. An error will be reported if the WCS in the NDF does not contain a pair of celestial sky axes.

  • Polygon: Each polygon will have, at most, 15 vertices. If the data is 2-dimensional, the polygon is a fit to the clump’ s outer boundary (the region containing all godo data values). If the data is 3-dimensional, the spatial footprint of each clump is determined by rejecting the least significant 10% of spatial pixels, where " significance" is measured by the number of spectral channels that contribute to the spatial pixel. The polygon is then a fit to the outer boundary of the remaining spatial pixels.

  • Ellipse: All data values in the clump are projected onto the spatial plane and " size" of the collapsed clump at four different position angles - all separated by 45 degrees - is found (see the OUTCAT parameter for a description of clump " size" ). The ellipse that generates the closest sizes at the four position angles is then found and used as the clump shape.

  • Ellipse2: The above method for determining ellipses works well for clumps that are in fact elliptical, but can generate extremely long thin ellipses for clumps are far from being ellitical. The " Ellipse2" option uses a different method for determining the best ellipse based on finding many marginal profiles at one degree intervals of azimuth, and using the longest marginal profile as the major axis. The ellipse is centred at the clump centroid.

  • Ellipse3: The same as " Ellipse2" except that the ellipse is centred at the clump peak, rather than the clump centroid, and the pixel data values are used as weights when forming the mean radial distance at each azimuth angle.

In general, ellipses will outline the brighter, inner regions of each clump, and polygons will include the fainter outer regions. [None]

TRUNC = _REAL (Read)
The level (above the local background) at which clumps should be truncated to zero, given as a fraction of the noise level specified by RMS. [current value]
UBND() = _INTEGER (Read)
The upper pixel bounds of the output NDF. The number of values supplied (1, 2 or 3) defines the number of pixel axes in the output NDF (an error is reported if the number of values supplied for LBND and UBND differ). If an NDF is supplied for parameter LIKE, the suggested defaults for this parameter will be the upper pixel bounds of the supplied NDF.
VELFWHM = _REAL (Read)
The FWHM of the Gaussian velocity resolution of the instrument, in pixels. The generated clumps are smoothed on the velocity axis with a Gaussian beam of this FWHM, before noise is added. No velocity smoothing is performed if VELFWHM is zero. See also parameter PRECAT. [current value]
VGRAD1( 2 ) = _REAL (Read)
Defines the distribution from which the projection of the internal velocity gradient vector onto pixel axis 1 of each clump is chosen. Values should be supplied in dimensionless units of " velocity pixels per spatial pixel" . See parameter PARDIST for additional information. [current value]
VGRAD2( 2 ) = _REAL (Read)
Defines the distribution from which the projection of the internal velocity gradient vector onto pixel axis 2 of each clump is chosen. Values should be supplied in dimensionless units of " velocity pixels per spatial pixel" . See parameter PARDIST for additional information. [current value]

Notes: