ms_intro.3

C编写的格式转换程序

.IP numsamples:
The number of samples pointed to by the 'datasamples' pointer.

.IP sampletype:
The type of samples pointed to by the 'datasamples' pointer.
Supported types are 'a' (ASCII), 'i' (integer), 'f' (float) and 'd'
(double).  The size of each sample type in bytes is returned
by the get_samplesize(3) lookup routine.

.IP prvtptr:
A private pointer for general use.  This pointer is not used by
libmseed and can safely be used by the calling program.

.IP ststate:
Pointer to a StreamState struct used internally to track stream
oriented state variables.  Memory for this only allocated when needed.

.IP next:
A pointer to the next MSTrace structure.  The value will be 0 for the
last link in a chain of MSTrace structures.

.SH LOG MESSAGES

All of the log and diagnostic messages emitted by the library
functions use the same interface.  The output from this interface can
be controlled.  This is useful when the library will be embedded in a
larger system with a custom logging facility.  See the man page for
more details.

.nf
  ms_log() : the central logging facility.  Behavior is controlled by
        the settings specified with ms_loginit().

  ms_loginit() : set the functions and prefixes used for log,
        diagnostic and error messages.
.fi

The default destination for log messages is standard output (stdout),
while all diagnostic (including error) messages go to standard error
(stderr).  Most of the internal messages emmited by the library are
considered diagnostic and will, by default, go to standard error.

The default prefix for log and diagnostic messages is nothing. The
default prefix for diagnostic error messages is "Error: ".

There are reentrant versions of these functions that operate directly
on a logging parameter MSLogParam struct.  These are intended for use
in threaded programs or where a complex logging scheme is desired.
See the man pages for more details.


.SH WAVEFORM DATA

Waveform data samples are managed by libmseed in a couple of different
formats depending on how they are unpacked or will be packed.  An
array of samples is completely represented by an array of sample
values, the number of samples and a sample type.  The number of
samples is always the actual number of sample values, not the number
of bytes needed for storing the values.  Samples can be either ASCII,
32-bit integer, 32-bit floats or 64-bit double precision floats.

Sample types are identified by a single ASCII type character:
.nf
"a" - ASCII (8 bits)
"i" - integer (32 bits)
"f" - float (32 bits)
"d" - double (64 bits)
.fi

The size of each sample type in bytes is returned by the
get_samplesize(3) lookup routine.

.SH BYTE ORDER

The SEED 2.4 standard allows data only SEED (Mini-SEED) to be either
in big (most significant byte first) or little (least significant byte
first) endian byte order.  Unfortunately it is not well defined what
little endian Mini-SEED really means.  While libmseed supports all
four combinations of big and little endian header and data the surest
way to avoid compatibility problems is to always create big endian
Mini-SEED records (header and data).

.B Reading MiniSEED - how libmseed determines the byte order of a record:

The byte order of a record header is determined by checking if the
record start year is a sane value (e.g. between 1920 and 2020).  The
byte order of (compressed) data samples is determined by the byte
order flag in the Blockette 1000, if a Blockette 1000 is not present
the byte order is assumed to be the same as the header.  To force the
byte order determination of either the header or data section of a
record the following environment variables can be set:

.nf
UNPACK_HEADER_BYTEORDER
UNPACK_DATA_BYTEORDER
.fi

These variables should be set to either 0 (little endian) or 1 (big
endian).  A programmatic equivalent of setting these environment
variables is provided via the following macros:

.nf
MS_UNPACKHEADERBYTEORDER(X)
MS_UNPACKDATABYTEORDER(X)
.fi

.B Writing MiniSEED - in what byte order libmseed creates records:

Normally the byte order of MiniSEED created by libmseed is controlled
via a flag in the API.  This byte order flag determines the ordering
for both the header and data sections of a record.  To force the byte
order of either the header or data section of a record the following
environment variables can be set:

.nf
PACK_HEADER_BYTEORDER
PACK_DATA_BYTEORDER
.fi

These variables should be set to either 0 (little endian) or 1 (big
endian).  A programmatic equivalent of setting these environment
variables is provided via the following macros:

.nf
MS_PACKHEADERBYTEORDER(X)
MS_PACKDATABYTEORDER(X)
.fi

Note that some interpretations of the SEED 2.4 format imply that
so-called little endian MiniSEED means that the record header is
little endian but that the data section is big endian (as the only
defined data encodings must be based on the SEED DDL which, in turn,
must be defined in terms of big endian).  Libmseed will not create
MiniSEED of this flavor by default but can be configured to do so by
setting the environment variables described above approriately.

.SH COMMON USAGE

Example programs using libmseed are provided in the 'examples'
directory of the source code distribution.

One of the most common tasks is to read a file of Mini-SEED records
and either perform some action based on the header values or apply
some process to the data samples.  This task is greatly simplified by
using the library functions ms_readmsr(3) and ms_readtraces(3).  The
ms_readmsr(3) routine will open a specified file and return MSRecord
structures for each Mini-SEED record it reads from the file.  The
ms_readtraces(3) routine will do the same except add all the data read
to a MSTraceGroup, this is ideal for quickly reading data for
processing.  Both of these routines are able to automatically detect
record length.

Skeleton code for reading a file with ms_readmsr(3):

.nf
main() {
  MSRecord *msr = NULL;
  int retcode;

  while ( (retcode = ms_readmsr (&msr, filename, 0, NULL, NULL, 1, 0, verbose)) == MS_NOERROR )
    {
       /* Do something with the record here, e.g. print */
       msr_print (msr, verbose);
    }

  if ( retcode != MS_ENDOFFILE )
    ms_log (2, "Cannot read %s: %s\n", filename, ms_errorstr(retcode));

  /* Cleanup memory and close file */
  ms_readmsr (&msr, NULL, 0, NULL, NULL, 0, 0);
}

.fi
For reading two files with ms_readtraces(3):
.nf

main() {
  MSTraceGroup *mstg = NULL;
  int retcode;

  retcode = ms_readtraces (&mstg, filename, 0, -1.0, -1.0, 0, 1, 0, verbose);

  if ( retcode != MS_ENDOFFILE )
    ms_log (2, "Cannot read %s: %s\n", filename, ms_errorstr(retcode));

  retcode = ms_readtraces (&mstg, filename2, 0, -1.0, -1.0, 0, 1, 0, verbose);

  if ( retcode != MS_ENDOFFILE )
    ms_log (2, "Cannot read %s: %s\n", filename2, ms_errorstr(retcode));

  if ( ! mstg )
    {
      fprintf (stderr, "Error reading file\\n");
      return -1;
    }

  /* Do something with the traces here, e.g. print */
  mst_printtracelist (mstg, 0, verbose, 0);

  mst_freegroup (&mstg);
}
.fi

Another common task is to create (pack) Mini-SEED records. The library
supports packing of Mini-SEED either from MSRecord structures, MSTrace
structures or MSTraceGroup collections using, respectively, msr_pack(3),
mst_pack(3) or mst_packgroup(3).  In each case the appropriate data
structure and parameters are provided to the routine along with a
function pointer to a routine that will be called each time a record
is complete and should be disposed of.

When packing Mini-SEED records the concept of a record header template
is used, the template is always in the form of a MSRecord structure.
This allows the calling program to dictate the contents, with a few
exceptions, of the header in the final data records.

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
\fBmsr_unpack(3)\fP, \fBms_time(3)\fP and \fBmsr_pack(3)\fP

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