SNDALTIM -- Interpolate a sounding to standard aviation altimeter settings
   SNDALTIM sdataset ddataset.pos <keywords>
Parameters:
   sdataset     | ADDE source dataset name.  Dataset schemas currently
                  handled are RAOB, IRAB, GRET, RAWI, RSIG, and IRSG.
   ddataset.pos | Local destination dataset and position.  Position is
                  required since output must go to a single local point
                  data file.
Keywords:
   FORM=   (selects a type of output, given a source dataset)
         FILE     | Lists files and observations available in
                                                   the source dataset
         PARAM    | Lists dataset parameter names
                        (handy when setting up SELECT= values)
         SOUND    | Writes and/or displays interpolated soundings (default)
   NUM=  number   | Sets a limit on the number of soundings processed
                        and sent to output (default=1)
         ALL      | Output all soundings satisfying the SELECT= criteria
   SELECT= 'param val1 val2; param val1,val2,val3'
            Note that station, day, and time are now specified in the
            SELECT= parameters and are no longer positional parameters.
            Defaults for day and time are whatever station, day, or time
            are first encountered in the source dataset that match the
            SELECT= conditions.  More than one day will not be written
            to the destination file, which only contains eight 3-hour
            intervals.  Put a DAY value into the SELECT= conditions if
            more than one day's data exists in the source dataset.
            Example:
              SELECT= 'IDN 72645 72660; TIME 0; DAY 97220'
              SELECT= 'IDN 72645, 72649, 72660; DAY 97220'
              SELECT= 'TIME 12; DAY 96037; IDN 72645'
              SELECT= 'TIME 0; LAT=40 50; LON=80 100'
            Every atmospheric level satisfying the SELECT= parameters
            will be returned by the server.  The client then groups the
            levels by STATION, DAY, and TIME and assembles them into
            a list of raw sounding data.  Each sounding in that list
            is edited, smoothed, and missing data is interpolated,
            using OPT=, before being returned to the client for output.
   SIG= NONE  | Do not search for any related significant datasets
                  to add to the mandatory sounding data returned
   OPT=        (Processing options available for soundings from server)
        0     | Mandatory levels only - no interpolation
        1     | Significant temperature and mandatory levels
        3     | Mandatory, significant temperature and significant wind
                levels; recomputes heights; computes wind pressure;
        5     | Significant temperature and mandatory levels; interpolates
                wind at significant temperature levels
        7     | Mandatory, significant temperature and significant wind
                levels; recomputes heights; fully interpolates for missing
                data (default)
   OUT=      (Output options available for altimeter levels)
          H     | Display interpolated sounding at 1000 foot intervals
                     and select for possible writing to destination file
          P     | Display sounding interpolated to
                     standard pressures above 18,000 feet and
                     select for possible writing to destination file
          S     | Display sounding levels in OPT= processed form
                     as returned from source dataset
          N     | Do not display any sounding data, even
                     if H or P is selected for output to a file
                     (default is "HPS" -- displays everything but
                      doesn't write to a destination point data file)
          F     | Write output to an IHGT schema destination point data
                     file at the indicated ddataset.position
          Note that the output options may be combined, i.e.
          "OUTPUT=SHF", "OUTPUT=HNF", or  "OUTPUT=SP", but "HPF"
          or "NF" will not write to a file because it is not clear
          which of the two kinds of interpolations is to be saved, and
          only one kind can be written into the reserved file space.
          The IHGT schema must be registered for output file access
          to work properly.  (Use the "SCHE DCIHGT" command.)
          At least 3 mandatory levels and less than 200 total levels
          are required to define a sounding for output.
   DEL=  YES   | Deletes existing file at ddataset.pos
         NO    | Will not write over an existing file (default)
   TITLE= 'text'  |  Title of destination point data file
                     ( def= 'Altimeter Interpolation: YYYYDDDD', where the
                       YYYYDDD is the SELECT= date from the input file )
Examples:
   SNDALTIM  GROUP/DESCR  FORM=FILE
                 (describes data available in the source dataset)
   SNDALTIM  GROUP/DESCR  SELECT='IDN 72269;DAY 97233'
                 (displays soundings at station 72269 on Aug. 21, 1997)
   SNDALTIM  GROUP/DESCR  SELECT='TIME 12'
                 (displays up to 10 soundings from dataset at 12UTC)
   SNDALTIM  SGR/D  DGR/D.4  SELECT='TIME 12'  NUM=ALL  OUTPUT=HF
                 (displays all interpolated soundings for time 12Z and
                  writes them to a destination dataset at position 4)
   SNDALTIM  SGR/D  DGR/D.2  NUM=800  OUT=NHF  DEL=YES
                 (collects and interpolates up to 800 soundings
                  and writes them to a point dataset at position 2
                  after deleting the local file originally at that
                  position)
Remarks:
   The output dataset file is structured in a spreadsheet fashion, with
   positions reserved for 1300 stations at 8 different times.  In many
   cases, only one or two times will be needed, or only a few hundred
   stations are required.  This can waste up to 80-90% of the reserved
   file space.  Until the data specified in the SELECT= clause is actually
   returned for all the stations and times asked for, and the bad levels
   and rejected soundings are edited out, there is no way of determining
   how much of the reserved space will actually be used for output.  Thus,
   an output dataset file can end up being very sparsely populated.

   Use the PTCOPY command to copy the destination dataset after running
   SNDALTIM.  It looks at the size of the dataset and removes any empty
   rows and columns during the copy:

                   "PTCOPY  ddataset  compressed_dataset"

   While returning mandatory records is reasonably fast (only 15 levels
   per sounding), some soundings with significant levels added can have
   up to 50 or 60 levels.  This can double or triple the running time
   of the SNDALTIM command, as well as the network bandwidth used --
   perhaps too much of a resource penalty.  It is suggested that the
   amount of data returned by the servers may be substantially reduced
   by selecting on parameters such as LAT and LON bounds, or ST and CO
   lists.  With less data to process, the SNDALTIM program will run much
   faster.
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