Classification of images

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.
We have for those reasons introduced the concept of ``Wild Card Replacement Character"; This character & may be used to build the output classification string in the following way: substring&n will be built by finding the n-th occurrence of the $\ast$ character in the classification rule, reading the content of the corresponding column and appending it to substring.

 

Table 15.5: MIDAS session for classifying SUSI exposures

Midas 001> CREATE/CRULE susi_ost BIAS

.. The Table Editor is invoked ..

Midas 002> READ/DESCR susi_ost.tbl BIAS

:IDENT.EQ."*BIAS*".AND.:EXPTIME.LE.1

Midas 003> CREATE/CRULE susi_ost FF

.. The Table Editor is invoked ..

Midas 004> READ/DESCR susi_ost.tbl FF

:IDENT.EQ."FF*"

Midas 005> CREATE/CRULE susi_ost SCI

.. The Table Editor is invoked ..

Midas 006> READ/DESCR susi_ost.tbl SCI

:IDENT.NE."*BIAS*".AND.:IDENT.NE."*FF*"

Midas 007> CLASSIFY/IMAGE susi_ost BIAS EXPTYPE BIAS

Midas 008> CLASSIFY/IMAGE susi_ost FF EXPTYPE FF

Midas 009> CLASSIFY/IMAGE susi_ost SCI EXPTYPE SCI

Midas 010> CREATE/CRULE susi_ost OPATH

.. The Table Editor is invoked ..

Midas 011> READ/DESCR susi_ost.tbl OPATH

:FILTER_NO.EQ."#*".AND.:FILTER_TYPE.EQ."FILTER*"

Midas 012> CLASSIFY/IMAGE susi_ost OPATH OPATH FILT_&1

 

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.
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:

:FILTB_ID.EQ."*".AND.:FILTB_TYP.EQ."FILTER*".AND.:GRATB_ID.EQ.""

The command

CLASSIFY/IMAGE ntt WFIB :OPATH FB&1

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.
Note:
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.