MST_PACK(3)

NAME
mst_pack - Packing of Mini-SEED records from MSTrace segments.

SYNOPSIS
#include <libmseed.h>

int  mst_pack ( MSTrace *mst,
                void (*record_handler) (char *, int, void *),
                void *handlerdata, int reclen, flag encoding,
                flag byteorder, int64_t *packedsamples, flag flush,
                flag verbose, MSRecord *mstemplate );

int  msr_packgroup ( MSTraceGroup *mstg,
                     void (*record_handler) (char *, int, void *),
                     void *handlerdata, int reclen, flag encoding,
                     flag byteorder, int64_t *packedsamples, flag flush,
                     flag verbose, MSRecord *mstemplate );

DESCRIPTION
mst_pack creates (packs) Mini-SEED data records from a MSTrace segment using the specified record length (reclen), Mini-SEED encoding and byteorder. Using mstemplate as a template, the common header fields and blockettes are packed into a record header. If no template will be used mstemplate 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).

reclen 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.

encoding 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.

byteorder 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 record_handler() 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 record_handler() to process the record, the memory will be re-used or freed when record_handler() returns. This function pointer is required, there is no other way to access the packed records.

The handlerdata pointer will be passed as the 3rd argument to record_handler(). This allows the caller to optionally pass data directly to the record_handler().

The integer pointed to by packedsamples will be set to the total number of samples packed.

If the flush 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 verbose flag controls verbosity, a value of zero will result in no diagnostic output.

mst_packgroup simply calls mst_pack for each MSTrace in the specified MSTraceGroup. The integer pointed to by packedsamples will be set to the total number of samples packed.

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 lastintsample member to the integer sample value that preceded the first sample in the current series and setting the comphistory flag to true (1).

RETURN VALUES
mst_pack returns the number records created on success and -1 on error.

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

CAVEATS
When using a MSRecord template (mstemplate) 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.

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

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, (char *)srcname);
    }
}

main() {
  int64_t 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 %"PRId64" samples into %d records,
             psamples, precords);

  mst_free (&mst);
}

SEE ALSO
ms_intro(3) and msr_pack(3).

AUTHOR
Chad Trabant
IRIS Data Management Center