Content-type: text/html Manpage of contsub


Section: User Commands (1)
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contsub - Subtract continuum from a datacube  




map manipulation  


CONTSUB is used to subtract the continuum from a datacube, which can be arbitrarily oriented. Several subtraction algorithms are possible, selected using the mode keyword. The maximum length of the frequency axis is 8192 pixels.  


This is the standard name for an input dataset -- usually an image, though sometimes either an image or visibility dataset or some foreign dataset format. Some tasks support multiple input datasets at a time (with wildcard supported) whereas others can handle only a single one at a time. There is generally no default input name.
This selects a subregion of an image. Multiple subregions can be selected, which are "ored" together. The following subcommands are recognized (each of which can be abbreviated to uniqueness).

Select image planes z1 to z2 inclusive. z2 defaults to z1.

Select the inner quarter of the image planes z1 to z2 inclusive. If both z1 and z2 are missing, then all planes are selected. If only z2 is omitted, z2 defaults to z1.

Select the pixels within a box with corners xmin,ymin,xmax,ymax. z1 and z2 are the same as in the "image" subcommand. If z1 and z2 are omitted, all planes are selected.

Select the pixels within the polygon defined by the list of vertices. z1 and z2 are the same as in the "image" subcommand. If z1 and z2 are missing, all planes are selected. If only z2 is omitted, it defaults to z1.

Select pixels according to the mask given in the file.

The units of the numbers given in the above commands are, in general, absolute pixels. But this can be changed (and rechanged) by using one of the following subcommands.

Coordinates are interpreted as absolute pixel values, the default.
Coordinates are relative to the reference pixel of the map.
Coordinates are relative to the central pixel of the map, (defined as (naxis1/2+1,naxis2/2+1)).
Coordinates are in arcseconds, relative to the reference pixel.
Coordinates in the third dimension are in km/s. Anything outside the region is untouched. (for the moment only rectangular boxes are recognized by contsub).
The name of the output dataset, either image or visibility. There is generally no default (although some tasks simply do not produce an output if this is not set). For modes poly, mean and avgs either this keyword or cont= must be specified, for mode subtr it must always be given. This output dataset will contain only those channels from the input dataset selected by the 'region' keyword.
An optional output dataset which will be one plane deep and contain the continuum map. For mode=poly, this is the interpolated map at the channel halfway between the first and last line channel selected. For mode=mean, it is the averaged image that was subtracted from the channel maps. For mode=avgs it is the average of the two average images that are calculated (see description of mode keyword). For mode=subtr this is an input set, which will be subtracted from each plane of the input dataset. For modes poly, mean and avgs either this keyword or out= must be specified, while for mode subtr it must always be given.
Select channels that supposedly contain continuum signal only. A selection is a list of ranges. A range is specified as (z1,z2), meaning channels z1 through z2, or as (z3) for a single channel. Ranges are separated by commas. E.g.: (z1,z2),(z3),(z4,z5). For options 'poly' (or 'mean'), the fit (or average), is done using all selected continuum channels. For option 'avgs', the selection of continuum channels must consist of two ranges. The 'contchan' keyword always refers to frequency channels, independent of whether the frequency axis is the 'z'-axis, the (Not used for mode='subtr').
Selects the continuum-determination algorithm. In each case the operation is done separately for each image pixel. May be abbreviated. The default is 'poly,1'.

continuum channels. The interpolated continuum intensity is subtracted from each separate channels. The maximum order is 8.

calculated and the average is subtracted from each channel. (equivalent to 'poly,0').

channels is calculated and a linear interpolation between the two averages is subtracted from each channel.

by cont= from the profile at the same position in the input dataset.

Select which output to write with the cont keyword. By default the continuum is written. If options=coeff,# one of the coefficients of the polynomial fit is written instead. '#' gives the order for which the coefficient is written (e.g. if cont=a+bx: 0='a', 1='b', etc).
verbose=true makes contsub print out some info every now and then.
For datacubes where the 'VELO' axis-identification does not occur in the header, this can be used to indicate which direction is the velocity (channel) axis. The value given must be one of 'x', 'y', not present, contsub assumes 'z'.




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Time: 18:35:38 GMT, July 05, 2011