title: Read a binary file using Numpy fromfile and a given offset
body: <p>I have a binary file which contains records of position of a plane.
  Each record look like:</p>
  
  <pre><code>0x00: Time, float32
  0x04: X, float32 // X axis position
  0x08: Y, float32 // Y axis position
  0x0C: Elevation, float32
  0x10: float32*4 = Quaternion (x,y,z axis and w scalar)
  0x20: Distance, float32 (unused)
  </code></pre>
  
  <p>So each record is 32 bytes long.</p>
  
  <p>I would like to get a Numpy array.</p>
  
  <p>At offset 1859 there is an unsigned int 32 (4 bytes) which indicates the number of elements of the array. 12019 in my case.</p>
  
  <p>I don't care (for now) header data (before offset 1859)</p>
  
  <p>Array only start at offset 1863 (=1859+4).</p>
  
  <p>I defined my own Numpy dtype like</p>
  
  <pre><code>dtype = np.dtype([
      ("time", np.float32),
      ("PosX", np.float32),
      ("PosY", np.float32),
      ("Alt", np.float32),
      ("Qx", np.float32),
      ("Qy", np.float32),
      ("Qz", np.float32),
      ("Qw", np.float32),
      ("dist", np.float32),
  ])
  </code></pre>
  
  <p>And I'm reading file using <code>fromfile</code>:</p>
  
  <pre><code>a_bytes = np.fromfile(filename, dtype=dtype)
  </code></pre>
  
  <p>But I don't see any parameter to provide to <code>fromfile</code> to pass offset.</p>