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The task parameter, region
, which gives the region-of-interest
consists of a combination of subcommands. Each subcommand
specifies either a subregion or the units of the coordinates used in subsequent
sub-commands.
The subregions selected by multiple subcommands are effectively `OR-ed' together to form the overall region. That is, the overall region selected is the `union' (not intersection) of the subregions.
For comparatively simple regions, combining subcommands is quite adequate. However for complex regions, a cursor-based program, cgcurs, may be the most convenient for generating the subcommands.
Region specification is composed of one or more of the following subcommands. Each subcommand can be abbreviated to uniqueness, and subcommands are separated by a comma.
box(xmin,ymin,xmax,ymax)is equivalent to
poly(xmin,ymin,xmax,ymin,xmax,ymax,xmin,ymax).z1 and z2 are the same as with the images and boxes subcommands.
The units used for the coordinates are controlled by the following subcommands:
For example, to specify a 21 by 21 region, centred on the reference pixel, use:
region=relpix,box(-10,-10,10,10)or to give a 10 by 10 region in the lower left corner of the image, use
region=box(1,1,10,10)If there are multiple maps in the file, use
region=box(1,1,10,10)(1,2)to select the first 2 maps.
The region-of-interest specifications can become
rather involved, when complex regions are used. As with visibility data selection,
@
files (see Section 2.5)
are a convenient way to store these.
There are some warnings for those accustomed to the select visibility data selection method:
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