mst_pack.3

C编写的格式转换程序

.TH MST_PACK 3 2007/08/16 "Libmseed API"
.SH DESCRIPTION
Packing of Mini-SEED records from MSTrace segments.

.SH SYNOPSIS
.nf
.B #include <libmseed.h>

.BI "int  \fBmst_pack\fP ( MSTrace *" mst ","
.BI "                void (*" record_handler ") (char *, int, void *),"
.BI "                void *" handlerdata ", int " reclen ", flag " encoding ","
.BI "                flag " byteorder ", int *" packedsamples ", flag " flush ","
.BI "                flag " verbose ", MSRecord *" mstemplate " );"

.BI "int  \fBmsr_packgroup\fP ( MSTraceGroup *" mstg ","
.BI "                     void (*" record_handler ") (char *, int, void *),"
.BI "                     void *" handlerdata ", int " reclen ", flag " encoding ","
.BI "                     flag " byteorder ", int *" packedsamples ", flag " flush ","
.BI "                     flag " verbose ", MSRecord *" mstemplate " );"
.fi

.SH DESCRIPTION
\fBmst_pack\fP creates (packs) Mini-SEED data records from a MSTrace
segment using the specified record length (\fIreclen\fP), Mini-SEED
\fIencoding\fP and \fIbyteorder\fP.  Using \fImstemplate\fP as a
template, the common header fields and blockettes are packed into a
record header.  If no template will be used \fImstemplate\fP should be
set to NULL.  A Blockette 1000 will be added if one is not present in
the template.  The MSTrace.datasamples array and MSTrace.numsamples value
will be adjusted (reduced) as samples are packed into data records.
This routine will modify the record length, encoding format, byte
order and sequence number of the MSRecord template.  The start time,
sample rate, data array, number of samples and sample type of the
MSRecord template are preserved.

Default values will be used for any of the key characteristics of
record length, encoding format and byte order that are -1.  The
default values are: reclen = 4096 bytes, encoding = 11 (Steim2) and
byteorder = 1 (MSBF or big-endian).

\fIreclen\fP should be set to the desired data record length in bytes
which must be expressible as 2 raised to the power of X where X is
between (and including) 8 to 20.

\fIencoding\fP should be set to one of the following supported
Mini-SEED data encoding formats: DE_ASCII (0), DE_INT16 (1), DE_INT32
(3), DE_FLOAT32 (4), DE_FLOAT64 (5), DE_STEIM1 (10) and DE_STEIM2
(11).  The encoding aliases are defined in libmseed.h.
MSTrace.sampletype should indicated the sample type as either 'a'
(ASCII), 'i' (32-bit integers), 'f' (32-bit floats) or 'd' (64-bit
doubles).

The encoding format must be appropriate for the sample type of the
MSTrace samples.  For example, Steim compression and integer encoding
formats require integer samples and float encoding formats require the
appropriate size floats as input.  As a counter example, float samples
cannot be packed using Steim compression or integer encoding formats.

\fIbyteorder\fP must be either 0 (LSBF or little-endian) or 1 (MBF or
big-endian).

Each time a complete record is packed it will be passed to the
\fIrecord_handler()\fP function which expects three arguments: 1) a
char * to the record buffer, 2) the length of the record in bytes and
3) a void pointer supplied by the caller.  It is the responsibility of
\fIrecord_handler()\fP to process the record, the memory will be
re-used or freed when \fIrecord_handler()\fP returns.  This function
pointer is required, there is no other way to access the packed
records.

The \fIhandlerdata\fP pointer will be passed as the 3rd argument to
\fIrecord_handler()\fP.  This allows the caller to optionally pass
data directly to the \fIrecord_handler()\fP.

The integer pointed to by \fIpackedsamples\fP will be set to the total
number of samples packed.

If the \fIflush\fP flag is not zero all of the data will be packed
into records, otherwise records will only be packed while there are
enough data samples to completely fill a record.

The \fIverbose\fP flag controls verbosity, a value of zero will result
in no diagnostic output.

\fBmst_packgroup\fP simply calls \fBmst_pack\fP for each MSTrace in the
specified MSTraceGroup.  The integer pointed to by \fIpackedsamples\fP
will be set to the total number of samples packed.

.SH COMPRESSION HISTORY
When the encoding format is Steim 1 or 2 compression contiguous
records will be created including compression history.  Put simply,
this means that the first difference in the compression series will be
the difference between the first sample of the current record and the
last sample of the previous record.  For the first record in a series
(no previous record), a so-called cold start, the first difference
will be zero.

The compression history can be seeded by allocating the StreamState
struct for the MSTrace and setting the \fBlastintsample\fP member to
the integer sample value that preceded the first sample in the current
series and setting the \fBcomphistory\fP flag to true (1).

.SH RETURN VALUES
\fBmst_pack\fP returns the number records created on success and -1 on
error.

\fBmst_packgroup\fP returns the total (for all MSTraces) number of
record created on success and -1 on error.

.SH CAVEATS
When using a MSRecord template (\fImstemplate\fP) the dataquality
member must be set to a valid value.  It is also advisable to set the
network, station, location and channel indicators to appropriate
values.  Unless these source indicators need to change they can simply
be copied from the matching MSTrace members.

.SH EXAMPLE
Skeleton code for creating (packing) Mini-SEED records with
mst_pack(3):

.nf
static void record_handler (char *record, int reclen, void *srcname) {
  if ( fwrite(record, reclen, 1, outfile) != 1 )
    {
      ms_log (2, "Error writing %s to output file\n", (char *)srcname);
    }
}

main() {
  int psamples;
  int precords;
  MSTrace *mst;
  char srcname[50];

  mst = mst_init (NULL);

  /* Populate MSTrace values */
  strcpy (mst->network, "XX");
  strcpy (mst->station, "TEST");
  strcpy (mst->channel, "BHE");
  mst->starttime = ms_seedtimestr2hptime ("2004,350,00:00:00.000000");
  mst->samprate = 40.0;

  /* The datasamples pointer and numsamples counter will be adjusted by
     the packing routine, the datasamples array must be dynamic memory
     allocated by the malloc() family of routines. */
  mst->datasamples = dataptr; /* pointer to 32-bit integer data samples */  
  mst->numsamples = 1234;
  mst->sampletype = 'i';      /* declare type to be 32-bit integers */

  mst_srcname (mst, srcname, 0);

  /* Pack 4096 byte, big-endian records, using Steim-2 compression */
  precords = mst_pack (mst, &record_handler, srcname, 4096, DE_STEIM2,
                       1, &psamples, 1, verbose, NULL);

  ms_log (0, "Packed %d samples into %d records\n", psamples, precords);

  mst_free (&mst);
}
.fi

.SH SEE ALSO
\fBms_intro(3)\fP and \fBmsr_pack(3)\fP.

.SH AUTHOR
.nf
Chad Trabant
IRIS Data Management Center
.fi