Provided by: libmseed-doc_2.19.8-1_all bug

NAME

       ms_intro - Introduction to libmseed

INTRODUCTION

       The Mini-SEED library provides a framework for manipulation of SEED data records including
       the unpacking and packing of data records.  Functionality is also  included  for  managing
       waveform data as continuous traces.  All structures of SEED 2.4 data records are supported
       with the following exceptions: Blockette 2000  opaque  data  which  has  an  unknown  data
       structure  by definition and Blockette 405 which depends on full SEED (SEED including full
       ASCII headers) for a full data description.

       The primary purpose of the library is to hide the details of Mini-SEED in order  to  allow
       rapid  development of Mini-SEED reading/writing software.  The framework allows everything
       from manipulation of Mini-SEED on a record-by-record basis to reading  of  Mini-SEED  into
       continuous trace segments to packing of large continuous traces using a record template.

       Certain  common tasks have, through library design, been streamlined, for example: reading
       Mini-SEED records from a file, adding data from unpacked records to a group of  traces  or
       packing a group of continuous traces into Mini-SEED records.

       The  following  data encoding formats are supported for both unpacking and packing: ASCII,
       INT16, INT32, FLOAT32, FLOAT64, STEIM1 and STEIM2.  The INT and FLOAT encodings each  have
       two  versions for quantities with a different number of bits of representation.  The STEIM
       decompression produces 32-bit integers; likewise the compression routines  require  32-bit
       integers  as input.  The following data encoding formats are supported for unpacking only:
       GEOSCOPE (24-bit, 16/3 and 16/4 gain ranged), CDSN, SRO and DWWSSN.

DATA RECORDS

       A Mini-SEED record is represented in the library using the  data  structure  given  below.
       This  structure  is  used  for  both  unpacking  and  packing  of Mini-SEED records.  When
       unpacking with msr_unpack(3) this structure is populated.  When packing  with  msr_pack(3)
       this  structure  is  used  as a template for the resulting data records and as a source of
       samples to be packed.

       Blockettes following the fixed section of the header are contained in the blockette  chain
       of  BlktLink structures.  Shortcut pointers to commonly used blockettes are maintained for
       types 100, 1000 and 1001.

       Many common header fields which are not easily accessible/usable in  the  raw  header  are
       available directly from the structure.  When this structure is used as a packing template,
       these common header fields are packed into the appropriate place in the fixed  section  or
       blockette.   As  examples,  the  ASCII  stream identifiers (network, station, location and
       channel) are available as NULL terminated strings, the start time is available as  a  high
       precision  epoch  time  (see  ms_time(3))  and  the  sample  rate is available as a double
       precision floating point value.

       The MSRecord data structure:

       typedef struct MSRecord_s {
         char           *record;            /* Mini-SEED record */
         int32_t         reclen;            /* Length of Mini-SEED record */

         /* Pointers to SEED data record structures */
         struct fsdh_s      *fsdh;          /* Fixed Section of Data Header */
         struct BlktLink    *blkts;         /* Root of blockette chain */
         struct blkt_100_s  *Blkt100;       /* Blockette 100, if present */
         struct blkt_1000_s *Blkt1000;      /* Blockette 1000, if present */
         struct blkt_1001_s *Blkt1001;      /* Blockette 1001, if present */

         /* Common header fields in accessible form */
         int32_t         sequence_number;   /* SEED record sequence number */
         char            dataquality;       /* Data quality indicator */
         char            network[11];       /* Network designation */
         char            station[11];       /* Station designation */
         char            location[11];      /* Location designation */
         char            channel[11];       /* Channel designation */
         hptime_t        starttime;         /* Record start time */
         double          samprate;          /* Nominal sample rate (Hz) */
         int64_t         samplecnt;         /* Number of samples in record */
         int8_t          encoding;          /* Data encoding format */
         int8_t          byteorder;         /* Byte order of record */

         /* Data sample fields */
         void           *datasamples;       /* Data samples */
         int64_t         numsamples;        /* Number of data samples */
         char            sampletype;        /* Sample type code: a, i, f, d */

         /* Stream oriented state information */
         StreamState    *ststate;           /* Stream processing state information */
       }
       MSRecord;

   Explanation of fields
       record:
              Pointer to the Mini-SEED record which was unpacked into the MSRecord.

       reclen:
              When unpacking this is the record length in bytes of the record pointed to  by  the
              'record' pointer.  When packing this is the length of records to pack.

       fsdh:  A  pointer  to  the  Fixed  Section  of the Data Header, all appropriate multi-byte
              quantities are in host byte order.

       blkts: The root of the blockette chain.  The chain is  constructed  from  linked  BlktLink
              structures.   All  appropriate  multi-byte quantities in the blockettes are in host
              byte order.  The msr_addblockette(3) routine can be used to add blockettes to  this
              chain.   The  BlktLink  structure  and  SEED  blockette  structures  are defined in
              libmseed.h.

       Blkt100:

       Blkt1000:

       Blkt1001:
              Shortcut pointers to  common  blockettes  in  the  blockette  chain.   If  a  given
              blockette does not exist in the blockette chain the shortcut pointer will be 0.  If
              more than one of these blockette types exist in the chain this pointer  will  point
              to the last one.

       sequence_number:
              SEED record sequence number, should be between 0 and 999999.

       dataquality:
              Data record and quality indicator, should be 'D', 'R', 'Q' or 'M'.

       network:

       station:

       location:

       channel:
              SEED stream identifiers as a NULL terminated strings.

       starttime:
              Record  start  time,  the  time of the first sample, as a high precision epoch time
              (see ms_time(3)).  This time can  be  converted  using  the  various  ms_hptime2<X>
              functions.

       samprate:
              The  sample  rate in samples per second in double precision.  During unpacking this
              value will be set to the sample rate given in the 100 blockette if it  is  present,
              otherwise  the  sample  rate  derived  from  the factor and multiplier in the fixed
              section of the header.  In a packing template this value will be used to  derive  a
              factor  and multiplier for the fixed section of the header and will be written into
              100 blockettes if any are in the blockette chain.

       samplecnt:
              The sample count, i.e. number of data samples in the record.

       encoding:
              The SEED data sample encoding format.  During packing  this  dictates  what  format
              will be used to pack the data samples.  Supported packing formats are 0 (DE_ASCII),
              1 (DE_INT16), 3 (DE_INT32), 4 (DE_FLOAT32), 5 (DE_FLOAT64), 10 (DE_STEIM1)  and  11
              (DE_STEIM2).

       byteorder:
              Byte  order  of multi-byte quantities in the record.  A value of 0 indicates little
              endian and a value of 1 indicates big endian.  During  packing  this  dictates  the
              byte order of the final records.

       datasamples:
              A pointer to the unpacked data samples.  If no data samples were unpacked this will
              be 0.  The 'numsamples' field indicates how many samples are in this array and  the
              'sampletype' field indicates what type of samples they are.

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

       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.

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

TRACES

       The library includes two facilities to manage collections of  continuous  trace  segments,
       each  represented  by  their  top  most  structure:  MSTraceGroup  and  MSTraceList.   The
       MSTraceList facility is a next generation version of the MSTraceGroup  facility.   Whereas
       the  MSTraceGroup  facility  uses  a  single  linked list of time segments the MSTraceList
       facility is slightly more complex with two  levels  of  linked  lists  and  common  access
       pointers.   The  advantages  are  that  the  MSTraceList  structure is faster to populate,
       especially when there are many segments (gappy data), and the list is always maintained in
       a sorted order.

TRACE LISTS

       MSTraceList  data  structures  allow  the  grouping  of  MSTraceID  structures  which  are
       themselves the root of MSTraceSeg structures, see  libmseed.h  as  a  reference  to  these
       structures.

TRACE GROUPS

       MSTraceGroup  data  structures  allow the grouping of MSTrace structures.  While a MSTrace
       structure is normally used to hold trace information and associated data  samples  it  can
       also be used without data samples as a means to keep trace of data coverage without actual
       samples.

       Numerous routines are provided for basic management of MSTrace structures,  including  the
       creation  of new MSTrace structures, adding data from Mini-SEED data structures to MSTrace
       structures, printing trace information, etc.

       The MSTraceGroup data structure acts as a very simple place to begin a  chain  of  MSTrace
       structures and keep track of the number of traces.

       The MSTrace and MSTraceGroup data structures:

       typedef struct MSTrace_s {
         char            network[11];     /* Network designation */
         char            station[11];     /* Station designation */
         char            location[11];    /* Location designation */
         char            channel[11];     /* Channel designation */
         char            dataquality;     /* Data quality indicator */
         char            type;            /* MSTrace type code */
         hptime_t        starttime;       /* Time of first sample */
         hptime_t        endtime;         /* Time of last sample */
         double          samprate;        /* Nominal sample rate (Hz) */
         int64_t         samplecnt;       /* Num. in trace coverage */
         void           *datasamples;     /* Data samples */
         int64_t         numsamples;      /* Num. samples in datasamples */
         char            sampletype;      /* Sample type code: a, i, f, d */
         void           *prvtptr          /* Private pointer for general use */
         struct MSTrace_s *next;          /* Pointer to next trace */
       }
       MSTrace;

       typedef struct MSTraceGroup_s {
         int32_t           numtraces;     /* Number of MSTraces in trace chain */
         struct MSTrace_s *traces;        /* Root of the trace chain */
       }
       MSTraceGroup;

   Explanation of fields
       dataquality:

              SEED  data  quality  indicator,  either  'D',  'R', 'Q' or 'M'.  This value will be
              (binary) 0 when the quality is unknown or mixed.

       network:

       station:

       location:

       channel:
              MSTrace identifiers as a NULL terminated strings.

       type:  A single character trace type indicator.  This field is not used  by  libmseed  but
              could be used for application specific trace identification.

       starttime:
              MSTrace  start  time,  the time of the first sample, as a high precision epoch time
              (see ms_time(3)).  This time can  be  converted  using  the  various  ms_hptime2<X>
              functions.

       endtime:
              MSTrace  end time, the time of the last sample, as a high precision epoch time (see
              ms_time(3)).  This time can be converted using the various ms_hptime2<X> functions.

       samprate:
              The sample rate in samples per second in double precision.

       samplecnt:
              The sample count, i.e. number of data samples in the trace.

       datasamples:
              A pointer to the data samples.  If no data samples are included  this  will  be  0.
              The  'numsamples'  field  indicates  how  many  samples  are  in this array and the
              'sampletype' field indicates what type of samples they are.

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

       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.

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

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

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

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.

         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.

       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.

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:
       "a" - ASCII (8 bits)
       "i" - integer (32 bits)
       "f" - float (32 bits)
       "d" - double (64 bits)

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

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).

       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:

       UNPACK_HEADER_BYTEORDER
       UNPACK_DATA_BYTEORDER

       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:

       MS_UNPACKHEADERBYTEORDER(X)
       MS_UNPACKDATABYTEORDER(X)

       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:

       PACK_HEADER_BYTEORDER
       PACK_DATA_BYTEORDER

       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:

       MS_PACKHEADERBYTEORDER(X)
       MS_PACKDATABYTEORDER(X)

       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 appropriately.

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.

       If your application is not designed to read Mini-SEED from files the library also provides
       functions to detect and parse Mini-SEED records in memory buffers.  For  more  information
       see ms_detect(3) and msr_parse(3).

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

       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: %s0, filename, ms_errorstr(retcode));

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

       For reading two files with ms_readtraces(3):

       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: %s0, 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: %s0, 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);
       }

       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):

       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;
         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; /* number of samples in array at dataptr */
         mst->samplecnt = mst->numsamples;
         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 records0,
                    psamples, precords);

         /* Disconnect datasamples pointer, otherwise mst_free() will free it */
         mst->datasamples = NULL;

         mst_free (&mst);
       }

SEE ALSO

       msr_unpack(3), ms_time(3) and msr_pack(3)

AUTHOR

       Chad Trabant
       IRIS Data Management Center

                                            2013/07/17                                MS_INTRO(3)