mb56 test data about mb-system

[schwehr]

I ended up using this script to filter the data for #322:

#!/usr/bin/env python2

import collections
import glob
import mmap
import os
import struct
import sys


class SimradFile(object):

    def __init__(self,filename):
        self.filename = filename
        tmp_file = open(filename, 'r+')
        self.size = os.path.getsize(filename)
        self.data = mmap.mmap(tmp_file.fileno(), self.size, access=mmap.ACCESS_READ)
    def __iter__(self):
        iter = SimradIterator(self)
        return iter

class SimradIterator(object):

    def __init__(self,simrad):
        self.data = simrad.data
        self.offset = 0
        self.file_size = simrad.size

    def __iter__(self):
        return self

    def next(self):
      return self.__next__()

    def __next__(self):
        if self.offset >= self.file_size:
            raise StopIteration
        dg_length = struct.unpack('I',self.data[self.offset:self.offset+4])[0]
        dg_id = self.data[self.offset+5]
        data = self.data[self.offset:self.offset + dg_length + 4]
        self.offset += 4 + dg_length
        return dg_id, data

c = collections.Counter()

with open('out.mb56', 'wb') as out:
  datagrams = 0
  for filenum, filename in enumerate(glob.glob(sys.argv[1])):
    print(filenum, filename)
    src = SimradFile(filename)
    for dg_id, data in src:
      datagrams += 1
      c[dg_id] += 1
      if c[dg_id] > 3:
        continue
      out.write(data)