msr_pack man page

msr_pack — Packing of Mini-SEED records.

Synopsis

#include <libmseed.h>

int       msr_pack ( MSRecord *msr,
                     void (*record_handler) (char *, int, void *),
                     void *handlerdata, int64_t *packedsamples,
                     flag flush, flag verbose );

int       msr_pack_header ( MSRecord *msr, flag normalize,
                            flag verbose );

Description

msr_pack creates (packs) Mini-SEED data records.  Using the record header values in a MSRecord data structure, msr, as a template, the common header fields and blockettes are packed into a record header.  A Blockette 1000 will be added if one is not present in the template.  The data samples at MSRecord.datasamples are packed in the encoding format indicated by the MSRecord.encoding field.  The MSRecord.datasamples array and MSRecord.numsamples value will not be changed by this routine.  It is the responsibility of the calling routine to adjust the data buffer if desired.  This routine will modify the start time and sequence number of the MSRecord template as it packs records.

The key characteristics of data record & quality indicator, record length, encoding format and byte order of packed records are taken from MSRecord.dataquality, MSRecord.reclen, MSRecord.encoding and MSRecord.byteorder respectively. Default values for these quantities will be used when the indicator is 0 or the reclen, encoding or byteorder are -1 respectively.  The default values are: dataquality = 'D', reclen = 4096 bytes, encoding = 11 (Steim2) and byteorder = 1 (MSBF or big-endian).

MSRecord.dataquality should be either 'D', 'R', 'Q' or 'M'.

MSRecord.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.

MSRecord.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.

MSRecord.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.  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.

MSRecord.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 not NULL.

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.

msr_pack_header packs header information, fixed section and blockettes, in a MSRecord structure into the Mini-SEED record at MSRecord.record.  This is useful for re-packing record headers after modification.  The normalize flag controls whether msr_normalize_header() is called before the header is packed. Normalizing updates the SEED structures associated with the MSRecord with values using the MSRecord base members (e.g. MSRecord.network, MSRecord.samplerate, etc.).  Normally this should be set to true (1) unless the associated SEED structures have been directly modified. The verbose flag controls verbosity, a value of zero will result in no diagnostic output.

Packing Overrides

The following macros and environment variables effect the packing of Mini-SEED:

Macros:
MS_PACKHEADERBYTEORDER(X)
MS_PACKDATABYTEORDER(X)

Environment variables:
PACK_HEADER_BYTEORDER
PACK_DATA_BYTEORDER

These macros and environment variables force the byte order of the header and data respectively.  They could be set to either 0 (little endian) or 1 (big endian).  Normally the byte order of the header and data is determined by the byteorder flag of the MSRecord, this capability is included to support any combination of byte orders in a generalized way.

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 MSRecord 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

msr_pack returns the number records created on success and -1 on error.

msr_pack_header returns the header length in bytes on success and -1 on error.

Example

Skeleton code for creating (packing) Mini-SEED records with msr_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 file0, (char *)srcname);
    }
}

main() {
  int64_t psamples;
  int precords;
  MSRecord *msr;
  char srcname[50];

  msr = msr_init (NULL);

  /* Populate MSRecord values */
  strcpy (msr->network, "XX");
  strcpy (msr->station, "TEST");
  strcpy (msr->channel, "BHE");
  msr->starttime = ms_seedtimestr2hptime ("2004,350,00:00:00.00");
  msr->samprate = 40.0;
  msr->reclen = 4096;         /* 4096 byte record length */
  msr->encoding = DE_STEIM2;  /* Steim 2 compression */
  msr->byteorder = 1;         /* big endian byte order */

  msr->datasamples = dataptr; /* pointer to 32-bit integer data samples */  
  msr->numsamples = 1234;
  msr->sampletype = 'i';      /* declare type to be 32-bit integers */

  msr_srcname (msr, srcname, 0);

  /* Pack the record(s) */
  precords = msr_pack (msr, &record_handler, srcname, &psamples, 1, verbose);

  ms_log (0, "Packed %"PRId64" samples into %d records0,
             psamples, precords);

  msr_free (&msr);
}

See Also

ms_intro(3), mst_pack(3), mst_packgroup(3), msr_normalize_header(3) and msr_unpack(3).

Author

Chad Trabant
IRIS Data Management Center

Referenced By

ms_intro(3), msr_addblockette(3), msr_init(3), msr_normalize_header(3), msr_unpack(3), mst_pack(3), ms_writemseed(3).

2013/05/17 Libmseed API