If BACKOFF is FALSE, a clump that sits on a high background level will have a larger reported width than an identical clump sitting on a lower background level. The position of the centroid may also be affected by the background level. This is usually undesirable, and so the default value for BACKOFF is usually TRUE. The main reason you may want to set BACKOFF to FALSE is if you want to compare clump properties found by FINDCLUMPS with those found by the IDL version of CLUMPFIND (which includes the background in its calculations). For this reason, the dynamic default value got BACKOFF is TRUE, unless METHOD is "ClumpFind" and the ClumpFind.IDLAlg configuration parameter is non-zero, in which case the dynamic default for BACKOFF is FALSE.
Note, the other reported clump properties such as total data value, peak data value, etc, are always based on the full clump data values, including background. 
The supplied value should be either a comma-separated list of strings or the name of a text file preceded by an up-arrow character "", containing one or more comma-separated list of strings. Each string is either a "keyword=value" setting, or the name of a text file preceded by an up-arrow character "". Such text files should contain further comma-separated lists which will be read and interpreted in the same manner (any blank lines or lines beginning with "#" are ignored). Within a text file, newlines can be used as delimiters as well as commas. Settings are applied in the order in which they occur within the list, with later settings over-riding any earlier settings given for the same keyword.
Each individual setting should be of the form:
where keyword has the form "algorithm.param"; that is, the name of the algorithm, followed by a dot, followed by the name of the parameter to be set. If the algorithm name is omitted, the current algorithm given by parameter METHOD is assumed. The parameters available for each algorithm are listed in the "Configuration Parameters" sections below. Default values will be used for any unspecified parameters. Assigning the value "def" (case insensitive) to a keyword has the effect of reseting it to its default value. Unrecognised options are ignored (that is, no error is reported). [current value]
The coordinate system used to describe the peak and centroid positions is determined by the value supplied for parameter WCSPAR. If WCSPAR is FALSE, then positions are specified in the pixel coordinate system of the input NDF. 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 WCSPAR is TRUE, then positions are specified in the current coordinate system of the input 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 input NDF.
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 corresponding pixel data value. For a Gaussian profile, this "size" value is equal to the standard deviation of the Gaussian. Optionally, the weights can be be based on the pixel data value after removal of the background - see parameter BACKOFF). If parameter DECONV is set TRUE, the values stored for "Size..." and "Peak" are corrected to take account of the smoothing introduced by the instrumental beam. These corrections reduced the "size..." values and increase the peak value. Beam sizes are specified by configuration parameters FWHMBeam and VeloRes.
For the GaussClump algorithm, the Sum and Volume values refer to the part of the Gaussian within the level defined by the GaussClump.ModelLim configuration parameter.
The values used for configuration parameters and ADAM parameters are written to the history information of the output catalogue.
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). [!]