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The two sets of selection criteria (``first choice'' and ``second choice'') have
to be entered in a table containing four columns:
- :FUNCTION -character column (max 256 char)

This column defines the different selection criteria and shall contain
mathematical expressions in which the variables may be the columns of the OST. The expression may contain arithmetic as well as
mathematical functions. On top of the operators and functions supported
by the SELECT/TABLE command, a new function REFVAL is available.
REFVAL(:col) will return the value of the column 'col' at the row corresponding
at the scientific exposure that is being processed. Suppose you try,
for instance, to associate exposures to the image susi0006.mt (Table 15.3), REFVAL(:MJD_LOC) will be 0.4582.
- :RANGE_1 -character column (max 256 char)

Contains the ranges defining the "first choice" selection
criteria.
- :RANGE_2 -character column (max 256 char)

Contains the ranges defining the second choice selection
criteria.
- :WEIGHT -real column

Defines the weighting factors for the different selection criteria.
These weights are used to rank the frames that satisfy the selection
criteria.

** Next:** An example of selection
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*Petra Nass*

*1999-06-15*