owlps/owlps-positioner/src/measurement.cc

/*
 * This file is part of the Owl Positioning System (OwlPS).
 * OwlPS is a project of the University of Franche-Comté
 * (Université de Franche-Comté), France.
 */


#include "measurement.hh"
#include "posexcept.hh"
#include "configuration.hh"

#include <iostream>
#include <sstream>

using namespace std ;



/* *** Constructors *** */


/**
 * Note that values pointed by #ap are not deleted.
 */
Measurement::~Measurement()
{
  ss_list.clear() ;
}



/* *** Read accessors *** */


/**
 * @returns The SS of the packet number \em pkt_id.
 * @returns 0 if the packet ID does not exist in the SS list.
 */
ss_t Measurement::get_ss(pkt_id_t pkt_id) const
{
  std::map<pkt_id_t, ss_t>::const_iterator ss = ss_list.find(pkt_id) ;
  if (ss == ss_list.end())
    return 0 ;
  return ss->second ;
}



/* *** Write accessors *** */


/**
 * @param packet_id The sequence number of the packet in the request,
 * as sent by the mobile.
 * @param ss_dbm The signal strength to add to #ss_list (in dBm).
 */
void Measurement::
add_ss(const pkt_id_t packet_id, const ss_t ss_dbm)
{
  // Add the new value (in dBm) along with the packet identifier:
  pair<pkt_id_t, ss_t> packet(make_pair(packet_id, ss_dbm)) ;
  if (! ss_list.insert(packet).second)
    {
      cerr
          << "Cannot insert the packet (#" << packet_id << ", "
          << static_cast<int_fast16_t>(ss_dbm) << " dBm)\n" ;
      return ;
    }

  // Update the average & variance with the new value:
  update_average(ss_dbm) ;
}


/**
 * Add an SS list to the current Measurement's SS list.
 * If the new SS list contains a packet with the same ID, the old one
 * is overwritten.
 */
void Measurement::
add_ss_list(const map<pkt_id_t, ss_t> &_ss_list)
{
  // We cannot use insert() here because we want to overwrite the
  // previous values with the same ID, if any.
  for (map<pkt_id_t, ss_t>::const_iterator
       i = _ss_list.begin() ; i != _ss_list.end() ; ++i)
    ss_list[i->first] = i->second ;

  recalculate_average() ;
}


/**
 * Merge consists of adding the SS values of \em source to #ss_list. It
 * is possible only if the #ap of the two Measurement are identical.
 * @throw cannot_merge if the AP of the two Measurement are different.
 */
void Measurement::merge(const Measurement &source)
{
  if (ap != source.ap)
    throw cannot_merge(
      "error when trying to merge measurements, APs are different") ;

  add_ss_list(source.ss_list) ;
}


/**
 * - #ap is not deleted, only initialised to NULL.
 * - #ss_list is cleared.
 * - #average_dbm, #average_mw and #variance are reset to 0.
 */
void Measurement::clear()
{
  ss_list.clear() ;
  average_dbm = 0 ;
  average_mw = 0 ;
  variance = 0 ;
  variance_m2 = 0 ;
  ap = NULL ;
}



/* *** Operations *** */


float Measurement::similarity(const Measurement &source) const
{
  string algorithm(
    Configuration::string_value("positioning.ss-similarity")) ;

  if (algorithm == "mean")
    return ss_square_distance(source) ;

  if (algorithm == "interval")
    {
      float
      interval_min = average_dbm - get_std_deviation(),
      interval_max = average_dbm + get_std_deviation() ;

      // Count the number of SS of source that are within the interval
      unsigned int nb_values = 0 ;
      for (map<pkt_id_t, ss_t>::const_iterator ss =
             source.ss_list.begin() ; ss != source.ss_list.end() ; ++ss)
        if (interval_min < ss->second && ss->second < interval_max)
          ++nb_values ;

      return 1 / nb_values ;
    }

  throw bad_configuration(
    "Bad SS similarity algorithm name \""+ algorithm +"\"!") ;
}


void Measurement::recalculate_average()
{
  average_dbm = 0 ;
  average_mw = 0 ;
  variance = 0 ;
  variance_m2 = 0 ;

  for (map<pkt_id_t, ss_t>::const_iterator
       i = ss_list.begin() ; i != ss_list.end() ; ++i)
    update_average(i->second) ;
}


void Measurement::update_average(ss_t ss_dbm)
{
  // Convert the new SS in mW:
  float ss_mw = pow(10, static_cast<float>(ss_dbm) / 10.0) ;

  // Update the average:
  float delta = ss_mw - average_mw ;
  average_mw += delta / ss_list.size() ;
  average_dbm = 10.0 * log10(average_mw) ;

  // Update the variance:
  variance_m2 += delta * (ss_mw - average_mw) ;
  if (ss_list.size() > 1)
    variance = variance_m2 / (ss_list.size() - 1) ;
}



/* *** Operators *** */


Measurement& Measurement::operator=(const Measurement &m)
{
  if (this == &m)
    return *this ;

  ap = m.ap ;
  ss_list = m.ss_list ;
  average_dbm = m.average_dbm ;
  average_mw = m.average_mw ;
  variance = m.variance ;
  variance_m2 = m.variance_m2 ;

  return *this ;
}


bool Measurement::operator==(const Measurement &m) const
{
  if (this == &m)
    return true ;

  return
    ap == m.ap &&
    ss_list == m.ss_list ;
}



const string Measurement::to_csv() const
{
  ostringstream csv_line ;

  if (ss_list.empty())
    return "" ;

  string mac_ap("") ;
  if (ap)
    mac_ap = ap->get_mac_addr() ;

  for (map<pkt_id_t, ss_t>::const_iterator
       i = ss_list.begin() ; i != ss_list.end() ; ++i)
    {
      if (i != ss_list.begin())
        csv_line << ';' ;
      csv_line
          << mac_ap << ';'
          << i->first << ';'
          << static_cast<int_fast16_t>(i->second) ;
    }

  return csv_line.str() ;
}



ostream &operator<<(ostream &os, const Measurement &m)
{
  // MAC address
  os
      << "AP: " << (m.ap ? m.ap->get_mac_addr() : "Unknown_AP")
      << ": " ;

  // List of SS
  if (m.ss_list.empty())
    os << "No values" ;
  else
    for (map<pkt_id_t, ss_t>::const_iterator
         i = m.ss_list.begin() ; i != m.ss_list.end() ; ++i)
      {
        if (i != m.ss_list.begin())
          os << ';' ;
        os << static_cast<int_fast16_t>(i->second)
           << '(' << i->first << ')' ;
      }
  os << " [AVG=" << m.average_dbm << "]" ;

  return os ;
}