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<H2><A NAME="SECTION002242000000000000000">
Classification of images</A>
</H2>
The classification process (command CLASSIFY/IMAGE) tags each frame with
one or more character strings
supplied by the user that classify the image in a unique way and will be
stored into columns
of the OST. For instance scientific exposures observed
in SUSI using the filter number 639 may be described`
with the two strings ``SCI" and ``FILT_639".
The practical problem is however that the very large number of different
possible optical elements mounted on
instruments like
EMMI/SUSI is not fixed in advance; for example, filters may be
added or changed. Clearly, one do not want to write classification
rules for all filter numbers or all combinations of grisms and gratings.
<BR>
We have for those reasons introduced the concept of ``<I>Wild Card Replacement
Character</I>";
This character & may be used to build the output classification string in
the following way:
<I>substring</I>&<I>n</I> will be built by finding the <I>n-th</I> occurrence of
the
<IMG
WIDTH="40" HEIGHT="54" ALIGN="BOTTOM" BORDER="0"
SRC="img897.gif"
ALT="$\ast$">
character in the classification rule, reading the content of the
corresponding column and appending it to <I>substring</I>.
<BR>
<DIV ALIGN="CENTER"><A NAME="17428"> </A>
<TABLE>
<CAPTION><STRONG>Table 15.5:</STRONG>
MIDAS session for classifying SUSI exposures</CAPTION>
<TR><TD>
<DIV ALIGN="CENTER">
<TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="LEFT">Midas 001> CREATE/CRULE susi_ost BIAS</TD>
</TR>
<TR><TD ALIGN="LEFT"><TT> <FONT SIZE="-2">.. The Table Editor is invoked .. </TT></FONT></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 002> READ/DESCR susi_ost.tbl BIAS</TD>
</TR>
<TR><TD ALIGN="LEFT"><B><FONT SIZE="-2"> :IDENT.EQ."*BIAS*".AND.:EXPTIME.LE.1</FONT></B></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 003> CREATE/CRULE susi_ost FF</TD>
</TR>
<TR><TD ALIGN="LEFT"><TT> <FONT SIZE="-2">.. The Table Editor is invoked .. </TT></FONT></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 004> READ/DESCR susi_ost.tbl FF</TD>
</TR>
<TR><TD ALIGN="LEFT"><B> <FONT SIZE="-2">:IDENT.EQ."FF*"</B> </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 005> CREATE/CRULE susi_ost SCI</TD>
</TR>
<TR><TD ALIGN="LEFT"><TT> <FONT SIZE="-2">.. The Table Editor is invoked .. </TT></FONT></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 006> READ/DESCR susi_ost.tbl SCI</TD>
</TR>
<TR><TD ALIGN="LEFT"><B> <FONT SIZE="-2">:IDENT.NE."*BIAS*".AND.:IDENT.NE."*FF*"</B> </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 007> CLASSIFY/IMAGE susi_ost BIAS EXPTYPE BIAS</TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 008> CLASSIFY/IMAGE susi_ost FF EXPTYPE FF</TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 009> CLASSIFY/IMAGE susi_ost SCI EXPTYPE SCI</TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 010> CREATE/CRULE susi_ost OPATH</TD>
</TR>
<TR><TD ALIGN="LEFT"><TT> <FONT SIZE="-2">.. The Table Editor is invoked .. </TT></FONT></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 011> READ/DESCR susi_ost.tbl OPATH</TD>
</TR>
<TR><TD ALIGN="LEFT"><B> <FONT SIZE="-2">:FILTER_NO.EQ."#*".AND.:FILTER_TYPE.EQ."FILTER*"</B> </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT">Midas 012> CLASSIFY/IMAGE susi_ost OPATH OPATH FILT_&1</TD>
</TR>
</TABLE></DIV>
<A NAME="midasproc"> </A></TD></TR>
</TABLE>
</DIV>
<BR>
<P>
Suppose you have created the classification rule WFIB for flagging all
exposures obtained in the blue arm of EMMI using the wide-field imaging mode.
Now you want to flag these exposures with a character string containing the
filter number that has been used.
<BR>
The corresponding descriptor WFIB of the OST may in natural language be:
``frame exposed in the blue arm using any filter and no grating"
The translated selected criterion looks as follows:
<BR><BLOCKQUOTE>
<TT>:FILTB_ID.EQ."*".AND.:FILTB_TYP.EQ."FILTER*".AND.:GRATB_ID.EQ.""</TT></BLOCKQUOTE>
<P>
The command <BLOCKQUOTE>
<TT>CLASSIFY/IMAGE ntt WFIB :OPATH FB&1</TT></BLOCKQUOTE>will flag all files in the OST ntt which satisfy this
selection criterion and will store in the column :OPATH the
character string obtained by appending
the contents of column :FILTB_ID to the string FB. The
classification given in the column :OPATH is obviously more convenient to use
than the original selection criteria.
<BR>
<TT>Note: <BR>
This implementation of the sofware expects, for the association
process, that the type of the exposures is stored in a column labeled :EXPTYPE
and that frames classified as scientific exposures are flagged with the string
SCI.</TT>
<P>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-15</I>
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