This tool generates a filter file by collating information from a number of different tables. Such a file may be used by the maketime FTOOL to produce good time intervals (GTIs), which may be used to filter event lists using the extractor or some other tool.
The input files must be in the "expanded HK" format, meaning that each quantity must be stored in a separate column, and there must be a column named "TIME", which gives the time stamp for each value. The rows must be sorted in TIME order, but do not have to be evenly spaced in TIME. Makefilter ignores rows with null TIME values.
Generally, the input files are spacecraft Housekeeping (HK) files, however they may contain any values as long as they have the correct format. For example, the "prefilter" HEAdas tool calculates a set of values derived from attitude and orbit data, which can be used as input to this tool.
The output filter file will be in the same "expanded HK" format as the input files - i.e. one column per filtering quantity and one TIME column. The rows of the filter file will not in general be evenly spaced. A value should be interpreted as being "in effect" from the time in its row, until the time of the following row. This means that the makefilter FTOOL should have the hidden parameters prefr=0.0 and postfr=1.0. As of LHEASOFT 5.3.1 the default for these parameters is 0.5. The columns will be in the same order as they are listed in the configuration file (see below). Any valid FITS column may be included in a filter file, including arrays and strings.
Makefilter examines each input column, and discards rows with null TIME values or with redundant column values. The filter file will contain all the undiscarded time values in all the input columns. If makefilter needs to write a column value for which there is no time in the input file, then it will interpolate using the method specified in the configuration file (see below). The first row in the filter file will always be equal to or before the first TSTART value in the input tables. Likewise, makefilter will write a row at the last TSTOP value in the input files, unless there is an input row later that this time.
The output columns will have the same TFORM, TSCALE, TZERO, and TNULL as the input column. Makefilter often needs to write null values for rows which come before or after an input file. So for integer columns, makefilter will arbitrarily choose a value for TNULL if one is not present in the input file. Note that makefilter does not check whether this value conflicts with legitimate data values in the input file. Bit field columns (TFORM "X") do not have a standard way to represent null values, so makefilter sets all bits to zero if a value is null.
Makefilter represents data internally using the data type which best matches the TFORM for the column. This could affect the interpolation accuracy, or the ability to use certain interpolation methods (see below). Step function interpolation will work with all column data types. Columns with TSCALE not equal to 1.0, or TZERO not equal to 0.0 are represented internally as floating point numbers.
The input files and columns are specified in a configuration file, formatted in either FITS or ASCII. The FITS format has a number of string-valued columns in the first extension of the file. The following columns must be present:
INCOL - the name of the column in the input file. If the column name begins with a "%", then this is interpreted as an expression calculated using the CFITSIO extended file name syntax. Note that only the expression should be given in the configuration file (no brackets). If a column does not exist, then makefilter aborts.
FILE - the name of the input FITS file. This should be just the name of the file, without extension or filtering specifications attached. Note that this file name will be prefixed with the value in the infileroot parameter. For many missions, the beginning of a file name indicates the mission and observation, while the end of the file indicates the file type. This way the same configuration file can be used for different observations by using a different infileroot parameter. If a file does not exist, makefilter issues a warning to stdout but continues to write a filter file without this column.
EXTENSION - The value of the EXTNAME keyword in the FITS extension containing the column you wish to read. Alternately this may be the number of the extension in the file, where the first extension is "1".
INTERP - The interpolation method applied to the input column. The currently available options are:
D - Indicates discrete, step function interpolation. A value in the input file is assumed to apply until the the time of the next row. There is no extrapolation, values before the first row or at or after the last row are set to null. This method should be used for quantities like flags which change instantaneously between discrete values.
I- Indicates linear interpolation. This method may give more accurate results for smoothly varying quantities. However, the output filter file is not interpolated, so the input file should already have sufficient rows to accurately represent the quantity using a step function. This method does not extrapolate.
OUTCOL - The name of the column in the output filter file. This is useful if the column names in the input files are not unique. If you specify "%", then the output column will have the same name as the input column.
COMMENT - This is the comment supplied for the TTYPE keyword for in the output filter file. If you specify "%", then makefilter will copy the comment from the input file. It is good form to provide a descriptive comment for each column, including a list of meanings for flag values if appropriate. Note however, that the number of characters in this comment is limited.
Any other columns will be ignored. Additional columns are discouraged, because they might conflict with future expansions of the configuration file format. There are no restrictions on the header keywords, other than those dictated by the FITS standard.
The ASCII configuration file has a set of whitespace delimited columns corresponding to the FITS columns as follows: "INCOL FILE EXTENSION INTERP % OUTCOL / COMMENT". Note the "%" is a mandatory, but currently unused column. The "/" indicates the beginning of the comment. Only the COMMENT value may contan whitespace.
The ASCII format is convenient if you need to create a configuration file on-the-fly in a script or if you will need to modify the configuration file frequently. However, the FITS configuration file allows you to provide additional metadata (e.g. CALDB keywords) in the FITS header.
The name of the configuration file describing the columns to copy into the filter file. The format of the configuration file is described above.
The prefix to prepend to all the file names in the configuration file. This allows you to use one configuration file for different datasets, if the dataset is identified by the beginning of the file name and the file type is identified by the end of the file name. If the configuration file contains complete file names, then this should be set to "".
The name of the output filter file which makefilter will create.
Verbosity of the tool
Overwrite exising output file?
Record parameters in filter file?
The value written to the TELESCOP keyword in the filter file. If this parameter is set to "", then makefilter will not write a TELESCOP keyword.