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public:documents:raw_olap_data_formats [2010-10-26 13:25] – Jan David Molpublic:documents:raw_olap_data_formats [2017-03-08 15:27] (current) – external edit 127.0.0.1
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-==== Raw OLAP data formats ====+===== Raw OLAP data formats (obsolete) ====
  
-OLAP produces several data formats, which are intended to be replaced by their final format, such as HDF5. The formats below are not officially supported and subject to change without notice.+OLAP produces several data formats, which are intended to be replaced by their final format, such as HDF5. 
 + 
 +===== After 2011-10-24 ===== 
 + 
 +Files adhere to the following naming scheme: ''Liiiii_SAPsssss_Bbbb_Sz_bf.raw'', with: 
 + 
 +  - ''iiiii'' = SAS observation ID 
 +  - ''sssss'' = Station beam number (SAP) 
 +  - ''bbb'' = Tied-array beam number (TAB) 
 +  - ''z'' = Stokes number 
 + 
 +The stokes numbers are to be interpreted as follows: 
 + 
 +  - Complex Voltages: 
 +     - z = 0 -> Xr (X polarisation, real part) 
 +     - z = 1 -> Xi (X polarisation, imaginary part) 
 +     - z = 2 -> Yr (Y polarisation, real part) 
 +     - z = 3 -> Yi (Y polarisation, imaginary part) 
 +  - Coherent/incoherent Stokes: 
 +     - z = 0 -> I 
 +     - z = 1 -> Q 
 +     - z = 2 -> U 
 +     - z = 3 -> V 
 + 
 +The data is encoded as follows. Each .raw file is a multiple of the following structure. All data is written as big-endian 32-bit IEEE floats. 
 + 
 +<code> 
 +struct block { 
 +  float sample[SUBBANDS][CHANNELS]; 
 +}; 
 +</code> 
 + 
 +The constants used can be derived from the parset: 
 + 
 +<code> 
 +  SUBBANDS = len(parset["Observation.subbandList"]) 
 + 
 +  if (complex voltages || coherent stokes) { 
 + 
 +    CHANNELS = parset["OLAP.CNProc_CoherentStokes.channelsPerSubband"] 
 +    if (CHANNELS == 0) CHANNELS = parset["Observation.channelsPerSubband"] 
 + 
 +  } elif (incoherent stokes) { 
 + 
 +    CHANNELS = parset["OLAP.CNProc_IncoherentStokes.channelsPerSubband"] 
 +    if (CHANNELS == 0) CHANNELS = parset["Observation.channelsPerSubband"] 
 + 
 +  } 
 +</code> 
 + 
 +The sampling rate can be derived as follows: 
 + 
 +<code> 
 +  # clock frequency (f.e. 200 MHz) 
 +  clock_hz = parset["Observation.sampleClock"] * 1.0e6 
 + 
 +  # subband frequency (f.e. 195 kHz) 
 +  base_subband_hz = clock_hz / 1024 
 + 
 +  # channel frequency (f.e. 763 Hz) 
 +  base_nrchannels = parset["Observation.channelsPerSubband"] 
 +  base_channel_hz = base_subband_hz / base_nrchannels 
 + 
 +  if(complex voltages || coherent stokes) { 
 +    cs_temporalintegration = parset["OLAP.CNProc_CoherentStokes.timeIntegrationFactor"] 
 + 
 +    sample_hz = base_channel_hz / cs_temporalintegration 
 + 
 +  } elif(incoherent stokes) { 
 + 
 +    is_temporalintegration = parset["OLAP.CNProc_IncoherentStokes.timeIntegrationFactor"] 
 + 
 +    sample_hz = base_channel_hz / is_temporalintegration 
 +  } 
 +     
 +</code> 
 + 
 +===== Before 2011-10-24 =====
  
 Data can be recorded as either complex voltages (yielding X and Y polarisations) or one or more stokes. In either case, a sequence of blocks will be stored, each of which consists of a header and data. The header is defined as: Data can be recorded as either complex voltages (yielding X and Y polarisations) or one or more stokes. In either case, a sequence of blocks will be stored, each of which consists of a header and data. The header is defined as:
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 in which sequence_number starts at 0, and is increased by 1 for every block. Missing sequence numbers implies missing data. The padding can have any value and is to be ignored. in which sequence_number starts at 0, and is increased by 1 for every block. Missing sequence numbers implies missing data. The padding can have any value and is to be ignored.
  
-== Complex Voltages ==+==== Complex Voltages ====
  
 Each (pencil) beam produces two files: one containing the X polarisation, and one containing the Y polarisation. The names of these files adhere to the following scheme: Each (pencil) beam produces two files: one containing the X polarisation, and one containing the Y polarisation. The names of these files adhere to the following scheme:
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 |Lxxxxx_Byyy_S0_bf.raw|X polarisations of beam yyy of observation xxxxx| |Lxxxxx_Byyy_S0_bf.raw|X polarisations of beam yyy of observation xxxxx|
 |Lxxxxx_Byyy_S1_bf.raw|Y polarisations of beam yyy of observation xxxxx| |Lxxxxx_Byyy_S1_bf.raw|Y polarisations of beam yyy of observation xxxxx|
 +
 +Proposed is the following scheme:
 +
 +|Lxxxxx_Byyy_S0_bf.raw|X polarisation (real part) of beam yyy of observation xxxxx|
 +|Lxxxxx_Byyy_S1_bf.raw|X polarisation (imaginary part) of beam yyy of observation xxxxx|
 +|Lxxxxx_Byyy_S2_bf.raw|Y polarisation (real part) of beam yyy of observation xxxxx|
 +|Lxxxxx_Byyy_S3_bf.raw|Y polarisation (imaginary part) of beam yyy of observation xxxxx|
  
 Each file is a sequence of blocks of the following structure: Each file is a sequence of blocks of the following structure:
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 struct block { struct block {
   struct header header;   struct header header;
 +
 +  /* each block contains SAMPLES samples. The data structure is two samples larger (|2) for
 +     technical reasons, but those two samples do not actually exist, and thus should be read
 +     and immediately discarded. Time should just be incremented SAMPLES samples per block. */
  
   /* big endian */   /* big endian */
 +  // 2010-09-20 release and later:
   fcomplex voltages[SAMPLES|2][SUBBANDS][CHANNELS];   fcomplex voltages[SAMPLES|2][SUBBANDS][CHANNELS];
 +
 +  /*
 +  // 2010-06-29 release and earlier stored data per subband instead of per beam:
 +  fcomplex voltages[BEAMS][CHANNELS][SAMPLES|2][POLARIZATIONS];
 +  */
 }; };
 </code> </code>
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   - filenames ended in -bf.raw instead of _bf.raw   - filenames ended in -bf.raw instead of _bf.raw
  
-== Coherent Stokes ==+==== Coherent Stokes ====
  
 Each (pencil) beam produces one or four files: one containing the Stokes I (power) values, and optionally three files for Stokes Q, U, and V, respectively. The names of these files adhere to the following scheme: Each (pencil) beam produces one or four files: one containing the Stokes I (power) values, and optionally three files for Stokes Q, U, and V, respectively. The names of these files adhere to the following scheme:
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 <code C> <code C>
 +// Since 2011-10-24, Stokes are just a continuous stream of samples:
 +struct block {
 +  float stokes[SAMPLES][SUBBANDS][CHANNELS];
 +};
 +
 +// Before 2011-10-24:
 struct block { struct block {
   struct header header;   struct header header;
 +
 +  /* each block contains SAMPLES samples. The data structure is two samples larger (|2) for
 +     technical reasons, but those two samples do not actually exist, and thus should be read
 +     and immediately discarded. Time should just be incremented SAMPLES samples per block. */
  
   /* big endian */   /* big endian */
 +  // 2010-09-20 release and later:
   float stokes[SAMPLES|2][SUBBANDS][CHANNELS];   float stokes[SAMPLES|2][SUBBANDS][CHANNELS];
 +
 +  /*
 +  // 2010-06-29 release and earlier stored data per subband instead of per beam:
 +  fcomplex voltages[BEAMS][CHANNELS][SAMPLES|2][STOKES];
 +  */ 
 }; };
 </code> </code>
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   - filenames ended in -bf.raw instead of _bf.raw   - filenames ended in -bf.raw instead of _bf.raw
  
-== Incoherent Stokes ==+==== Incoherent Stokes ====
  
 Incoherent stokes are stored per subband, with one or four stokes per file, using the following naming convention: Incoherent stokes are stored per subband, with one or four stokes per file, using the following naming convention:
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 struct block { struct block {
   struct header header;   struct header header;
 +
 +  /* each block contains SAMPLES samples. The data structure is two samples larger (|2) for
 +     technical reasons, but those two samples do not actually exist, and thus should be read
 +     and immediately discarded. Time should just be incremented SAMPLES samples per block. */\
  
   /* big endian */   /* big endian */
 +  // 2010-10-25 release and later:
   float stokes[STOKES][CHANNELS][SAMPLES|2];   float stokes[STOKES][CHANNELS][SAMPLES|2];
  
-  /* 2010-09-20 and earlier:+  /* 
 +  // 2010-09-20 release:
   float stokes[STOKES][SAMPLES|2][CHANNELS];   float stokes[STOKES][SAMPLES|2][CHANNELS];
 +
 +  // 2010-06-29 release and earlier:
 +  float stokes[CHANNELS][SAMPLES|2][STOKES];
   */   */
 }; };
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   - data order changed   - data order changed
  
 +==== BFRaw format ====
 +
 +Raw station data can be stored in a format called BFRaw. This format is used for debugging purposes and is not a regular observation mode, it takes more manpower to record it. The BFRaw format is recorded below for those who need to access it.
 +
 +A BFRaw file starts with a file header containing the configuration:
 +
 +<code C>
 +struct file_header
 +{
 +  // 0x3F8304EC, also determines endianness
 +  uint32_t    magic;
 +  // The number of bits per sample (16)
 +  uint8_t     bitsPerSample;
 +  // The number of polarizations (2)
 +  uint8_t     nrPolarizations;
 +  // Number of subbands, maximum of 62
 +  uint16_t    nrSubbands;
 +  // 155648 (160Mhz) or 196608 (200Mhz)
 +  uint32_t    nrSamplesPerSubband;
 +  // Name of the station
 +  char      station[20];
 +  // The sample rate: 156250.0 or 195312.5 .. double (number of samples per second for each subband)
 +  double   sampleRate;
 +  // The frequencies within a subband
 +  double   subbandFrequencies[62];
 +  // The beam pointing directions (RA, DEC in J2000)
 +  double   beamDirections[8][2];
 +  // mapping from subbands to beams (SAPs)
 +  int16_t     subbandToSAPmapping[62];
 +  // Padding to circumvent 8-byte alignment
 +  uint32_t    padding;
 +};
 +</code>
 +
 +After the file header, there is a series of blocks until the end of file, configured using values from the file header:
 +
 +<code C>
 +struct block
 +  // 0x2913D852
 +  uint32_t      magic;
 +
 +  // per-SAP information (up to 8 SAPs can be defined, but typically only 1 is used)
 +
 +  // number of samples the signal is shifted to align the station beam to the reference
 +  // phase center (=Observation.referencePhaseCenter in the parset)
 +  int32_t       coarseDelayApplied[8]; 
 +  // Padding to circumvent 8-byte alignment
 +  uint8_t       padding[4];
 +
 +  // the sub-sample delay which still has to be compensated for (in seconds),
 +  // at the beginning and at the end of the block
 +  double     fineDelayRemainingAtBegin[8];
 +  double     fineDelayRemainingAfterEnd[8];
 +  // Compatible with TimeStamp class (see below)
 +  int64_t      time[8];
 +
 +  struct marshalledFlags
 +  {
 +    // up to 16 ranges of flagged samples within this block
 +    uint32_t      nrFlagsRanges;
 +    struct range
 +    {
 +      uint32_t    begin; // inclusive
 +      uint32_t    end;   // exclusive
 +    } flagsRanges[16];
 +  } flags[8];
 +
 +  std::complex<int16_t>
 +    samples[fileHeader.nrSubbands][fileHeader.nrSamplesPerSubband][fileHeader.nrPolarizations];
 +};
 +</code>
 +
 +To convert a TimeStamp-compatible int64_t to a C-readable timestamp, use
 +<code C>
 +/* clockspeed is in Hz */
 +int64 nanoseconds = (int64) (timestamp * 1024 * 1e9 / clockspeed);
 +
 +struct timespec ts;
 +ts.tv_sec  = nanoseconds / 1000000000ULL;
 +ts.tv_nsec = nanoseconds % 1000000000ULL;
 +</code>
  
 ==== Types and constants ==== ==== Types and constants ====
  • Last modified: 2010-10-26 13:25
  • by Jan David Mol