urg_c_wrapper.cpp

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/*
 * Copyright (c) 2013, Willow Garage, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the Willow Garage, Inc. nor the names of its
 *       contributors may be used to endorse or promote products derived from
 *       this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Author: Chad Rockey, Mike O'Driscoll
 */

#include "ros/ros.h"
#include <urg_node/urg_c_wrapper.h>
#include <limits>
#include <string>
#include <vector>
#include <boost/crc.hpp>

namespace urg_node
{

URGCWrapper::URGCWrapper(const std::string& ip_address, const int ip_port, bool& using_intensity, bool& using_multiecho)
{
  // Store for comprehensive diagnostics
  ip_address_ = ip_address;
  ip_port_ = ip_port;
  serial_port_ = "";
  serial_baud_ = 0;


  long baudrate_or_port = (long)ip_port;
  const char *device = ip_address.c_str();

  int result = urg_open(&urg_, URG_ETHERNET, device, baudrate_or_port);
  if (result < 0)
  {
    std::stringstream ss;
    ss << "Could not open network Hokuyo:\n";
    ss << ip_address << ":" << ip_port << "\n";
    ss << urg_error(&urg_);
    throw std::runtime_error(ss.str());
  }

  initialize(using_intensity, using_multiecho);
}

URGCWrapper::URGCWrapper(const int serial_baud, const std::string& serial_port,
    bool& using_intensity, bool& using_multiecho)
{
  // Store for comprehensive diagnostics
  serial_baud_ = serial_baud;
  serial_port_ = serial_port;
  ip_address_ = "";
  ip_port_ = 0;

  long baudrate_or_port = (long)serial_baud;
  const char *device = serial_port.c_str();

  int result = urg_open(&urg_, URG_SERIAL, device, baudrate_or_port);
  if (result < 0)
  {
    std::stringstream ss;
    ss << "Could not open serial Hokuyo:\n";
    ss << serial_port << " @ " << serial_baud << "\n";
    ss << urg_error(&urg_);
    stop();
    urg_close(&urg_);
    throw std::runtime_error(ss.str());
  }

  initialize(using_intensity, using_multiecho);
}

void URGCWrapper::initialize(bool& using_intensity, bool& using_multiecho)
{
  int urg_data_size = urg_max_data_size(&urg_);
  // urg_max_data_size can return a negative, error code value. Resizing based on this value will fail.
  if (urg_data_size < 0)
  {
    urg_.last_errno = urg_data_size;
    std::stringstream ss;
    ss << "Could not initialize Hokuyo:\n";
    ss << urg_error(&urg_);
    stop();
    urg_close(&urg_);
    throw std::runtime_error(ss.str());
  }
  // Ocassionally urg_max_data_size returns a string pointer, make sure we don't allocate too much space,
  // the current known max is 1440 steps
  if (urg_data_size  > 5000)
  {
    urg_data_size = 5000;
  }
  data_.resize(urg_data_size * URG_MAX_ECHO);
  intensity_.resize(urg_data_size * URG_MAX_ECHO);

  started_ = false;
  frame_id_ = "";
  first_step_ = 0;
  last_step_ = 0;
  cluster_ = 1;
  skip_ = 0;

  if (using_intensity)
  {
    using_intensity = isIntensitySupported();
  }

  if (using_multiecho)
  {
    using_multiecho = isMultiEchoSupported();
  }

  use_intensity_ = using_intensity;
  use_multiecho_ = using_multiecho;

  measurement_type_ = URG_DISTANCE;
  if (use_intensity_ && use_multiecho_)
  {
    measurement_type_ = URG_MULTIECHO_INTENSITY;
  }
  else if (use_intensity_)
  {
    measurement_type_ = URG_DISTANCE_INTENSITY;
  }
  else if (use_multiecho_)
  {
    measurement_type_ = URG_MULTIECHO;
  }
}

void URGCWrapper::start()
{
  if (!started_)
  {
    int result = urg_start_measurement(&urg_, measurement_type_, 0, skip_);
    if (result < 0)
    {
      std::stringstream ss;
      ss << "Could not start Hokuyo measurement:\n";
      if (use_intensity_)
      {
        ss << "With Intensity" << "\n";
      }
      if (use_multiecho_)
      {
        ss << "With MultiEcho" << "\n";
      }
      ss << urg_error(&urg_);
      throw std::runtime_error(ss.str());
    }
  }
  started_ = true;
}

void URGCWrapper::stop()
{
  urg_stop_measurement(&urg_);
  started_ = false;
}

URGCWrapper::~URGCWrapper()
{
  stop();
  urg_close(&urg_);
}

bool URGCWrapper::grabScan(const sensor_msgs::LaserScanPtr& msg)
{
  msg->header.frame_id = frame_id_;
  msg->angle_min = getAngleMin();
  msg->angle_max = getAngleMax();
  msg->angle_increment = getAngleIncrement();
  msg->scan_time = getScanPeriod();
  msg->time_increment = getTimeIncrement();
  msg->range_min = getRangeMin();
  msg->range_max = getRangeMax();

  // Grab scan
  int num_beams = 0;
  long time_stamp = 0;
  unsigned long long system_time_stamp = 0;

  if (use_intensity_)
  {
    num_beams = urg_get_distance_intensity(&urg_, &data_[0], &intensity_[0], &time_stamp, &system_time_stamp);
  }
  else
  {
    num_beams = urg_get_distance(&urg_, &data_[0], &time_stamp, &system_time_stamp);
  }
  if (num_beams <= 0)
  {
    return false;
  }

  // Fill scan
  msg->header.stamp.fromNSec((uint64_t)system_time_stamp);
  msg->header.stamp = msg->header.stamp + system_latency_ + user_latency_ + getAngularTimeOffset();
  msg->ranges.resize(num_beams);
  if (use_intensity_)
  {
    msg->intensities.resize(num_beams);
  }

  for (int i = 0; i < num_beams; i++)
  {
    if (data_[(i) + 0] != 0)
    {
      msg->ranges[i] = static_cast<float>(data_[i]) / 1000.0;
      if (use_intensity_)
      {
        msg->intensities[i] = intensity_[i];
      }
    }
    else
    {
      msg->ranges[i] = std::numeric_limits<float>::quiet_NaN();
      continue;
    }
  }
  return true;
}

bool URGCWrapper::grabScan(const sensor_msgs::MultiEchoLaserScanPtr& msg)
{
  msg->header.frame_id = frame_id_;
  msg->angle_min = getAngleMin();
  msg->angle_max = getAngleMax();
  msg->angle_increment = getAngleIncrement();
  msg->scan_time = getScanPeriod();
  msg->time_increment = getTimeIncrement();
  msg->range_min = getRangeMin();
  msg->range_max = getRangeMax();

  // Grab scan
  int num_beams = 0;
  long time_stamp = 0;
  unsigned long long system_time_stamp;

  if (use_intensity_)
  {
    num_beams = urg_get_multiecho_intensity(&urg_, &data_[0], &intensity_[0], &time_stamp, &system_time_stamp);
  }
  else
  {
    num_beams = urg_get_multiecho(&urg_, &data_[0], &time_stamp, &system_time_stamp);
  }
  if (num_beams <= 0)
  {
    return false;
  }

  // Fill scan (uses vector.reserve wherever possible to avoid initalization and unecessary memory expansion)
  msg->header.stamp.fromNSec((uint64_t)system_time_stamp);
  msg->header.stamp = msg->header.stamp + system_latency_ + user_latency_ + getAngularTimeOffset();
  msg->ranges.reserve(num_beams);
  if (use_intensity_)
  {
    msg->intensities.reserve(num_beams);
  }

  for (size_t i = 0; i < num_beams; i++)
  {
    sensor_msgs::LaserEcho range_echo;
    range_echo.echoes.reserve(URG_MAX_ECHO);
    sensor_msgs::LaserEcho intensity_echo;
    if (use_intensity_)
    {
      intensity_echo.echoes.reserve(URG_MAX_ECHO);
    }
    for (size_t j = 0; j < URG_MAX_ECHO; j++)
    {
      if (data_[(URG_MAX_ECHO * i) + j] != 0)
      {
        range_echo.echoes.push_back(static_cast<float>(data_[(URG_MAX_ECHO * i) + j]) / 1000.0f);
        if (use_intensity_)
        {
          intensity_echo.echoes.push_back(intensity_[(URG_MAX_ECHO * i) + j]);
        }
      }
      else
      {
        break;
      }
    }
    msg->ranges.push_back(range_echo);
    if (use_intensity_)
    {
      msg->intensities.push_back(intensity_echo);
    }
  }

  return true;
}

bool URGCWrapper::getAR00Status(URGStatus& status)
{
  // Construct and write AR00 command.
  std::string str_cmd;
  str_cmd += 0x02;  // STX
  str_cmd.append("000EAR00A012");  // AR00 cmd with length and checksum.
  str_cmd += 0x03;  // ETX

  // Get the response
  std::string response = sendCommand(str_cmd);

  ROS_DEBUG_STREAM("Full response: " << response);

  // Strip STX and ETX before calculating the CRC.
  response.erase(0, 1);
  response.erase(response.size() - 1, 1);

  // Get the CRC, it's the last 4 chars.
  std::stringstream ss;
  ss << response.substr(response.size() - 4, 4);
  uint16_t crc;
  ss >> std::hex >> crc;

  // Remove the CRC from the check.
  std::string msg = response.substr(0, response.size() - 4);
  // Check the checksum.
  uint16_t checksum_result = checkCRC(msg.data(), msg.size());

  if (checksum_result != crc)
  {
    ROS_WARN("Received bad frame, incorrect checksum");
    return false;
  }

  // Debug output reponse up to scan data.
  ROS_DEBUG_STREAM("Response: " << response.substr(0, 41));
  // Decode the result if crc checks out.
  // Grab the status
  ss.clear();
  ROS_DEBUG_STREAM("Status " << response.substr(8, 2));
  ss << response.substr(8, 2);  // Status is 8th position 2 chars.
  ss >> std::hex >> status.status;

  if (status.status != 0)
  {
    ROS_WARN("Received bad status");
    return false;
  }

  // Grab the operating mode
  ss.clear();
  ROS_DEBUG_STREAM("Operating mode " << response.substr(10, 1););
  ss << response.substr(10, 1);
  ss >> std::hex >> status.operating_mode;

  // Grab the area number
  ss.clear();
  ss << response.substr(11, 2);
  ROS_DEBUG_STREAM("Area Number " << response.substr(11, 2));
  ss >> std::hex >> status.area_number;
  // Per documentation add 1 to offset area number
  status.area_number++;

  // Grab the Error Status
  ss.clear();
  ss << response.substr(13, 1);
  ROS_DEBUG_STREAM("Error status " << response.substr(13, 1));
  ss >> std::hex >> status.error_status;


  // Grab the error code
  ss.clear();
  ss << response.substr(14, 2);
  ROS_DEBUG_STREAM("Error code " << std::hex << response.substr(14, 2));
  ss >> std::hex >> status.error_code;
  // Offset by 0x40 is non-zero as per documentation
  if (status.error_code != 0)
  {
     status.error_code += 0x40;
  }

  // Get the lockout status
  ss.clear();
  ss << response.substr(16, 1);
  ROS_DEBUG_STREAM("Lockout " << response.substr(16, 1));
  ss >> std::hex >> status.lockout_status;

  return true;
}

bool URGCWrapper::getDL00Status(UrgDetectionReport& report)
{
  // Construct and write DL00 command.
  std::string str_cmd;
  str_cmd += 0x02;  // STX
  str_cmd.append("000EDL005BCB");  // DL00 cmd with length and checksum.
  str_cmd += 0x03;  // ETX

  // Get the response
  std::string response = sendCommand(str_cmd);

  ROS_DEBUG_STREAM("Full response: " << response);

  // Strip STX and ETX before calculating the CRC.
  response.erase(0, 1);
  response.erase(response.size() - 1, 1);

  // Get the CRC, it's the last 4 chars.
  std::stringstream ss;
  ss << response.substr(response.size() - 4, 4);
  uint16_t crc;
  ss >> std::hex >> crc;

  // Remove the CRC from the check.
  std::string msg = response.substr(0, response.size() - 4);
  // Check the checksum.
  uint16_t checksum_result = checkCRC(msg.data(), msg.size());

  if (checksum_result != crc)
  {
    ROS_WARN("Received bad frame, incorrect checksum");
    return false;
  }

  // Decode the result if crc checks out.
  // Grab the status
  uint16_t status = 0;
  ss.clear();
  ROS_DEBUG_STREAM("Status " << response.substr(8, 2));
  ss << response.substr(8, 2);  // Status is 8th position 2 chars.
  ss >> std::hex >> status;

  if (status != 0)
  {
    ROS_WARN("Received bad status");
    return false;
  }

  std::vector<UrgDetectionReport> reports;
  msg = msg.substr(10);  // remove the header.
  // Process the message, there are 29 reports.
  // The 30th report is a circular buff marker of area with 0xFF
  // denoting the "last" report being the previous one.
  for (int i = 0; i < 30; i++)
  {
    uint16_t area = 0;
    uint16_t distance = 0;
    uint16_t step = 0;
    ss.clear();

    // Each msg is 64 chars long, offset which
    // report is being read in.
    uint16_t offset_pos = i * 64;
    ss << msg.substr(offset_pos, 2);  // Area is 2 chars long
    ss >> std::hex >> area;


    ss.clear();
    ss << msg.substr(offset_pos + 4, 4);  // Distance is offset 4 from beginning, 4 chars long.
    ss >> std::hex >> distance;

    ss.clear();
    ss << msg.substr(offset_pos + 8, 4);  // "Step" is offset 8 from beginning 4 chars long.
    ss >> std::hex >> step;
    ROS_DEBUG_STREAM(i << " Area: " << area << " Distance: " << distance << " Step: " << step);

    UrgDetectionReport r;
    r.area = area;
    r.distance = distance;
    // From read value to angle of report is a value/8.
    r.angle = static_cast<float>(step) / 8.0;

    reports.push_back(r);
  }

  for (auto iter = reports.begin(); iter != reports.end(); ++iter)
  {
    // Check if value retrieved for area is FF.
    // if it is this is the last element lasers circular buffer.
    if (iter->area == 0xFF)
    {
      // Try and read the previous item.
      // if it's the beginning, then all reports
      // are empty.
      if (iter - 1 == reports.begin())
      {
        ROS_WARN("All reports are empty, no detections available.");
        report.status = status;
        return false;
      }
      if (iter - 1 != reports.begin())
      {
        report = *(iter-1);
        report.area += 1;  // Final area is offset by 1.
        report.status = status;
        break;
      }
    }
  }

  return true;
}


uint16_t URGCWrapper::checkCRC(const char* bytes, const uint32_t size)
{
  boost::crc_optimal<16, 0x1021, 0, 0, true, true>  crc_kermit_type;
  crc_kermit_type.process_bytes(bytes, size);
  return crc_kermit_type.checksum();
}

std::string URGCWrapper::sendCommand(std::string cmd)
{
  std::string result;
  bool restart = false;

  if (isStarted())
  {
    restart = true;
    // Scan must stop before sending a command
    stop();
  }

  // Get the socket reference and send
  int sock = urg_.connection.tcpclient.sock_desc;
  write(sock, cmd.c_str(), cmd.size());

  // All serial command structures start with STX + LEN as
  // the first 5 bytes, read those in.
  size_t total_read_len = 0;
  size_t read_len = 0;
  // Read in the header, make sure we get all 5 bytes expcted
  char recvb[5] = {0};
  ssize_t expected_read = 5;
  while (total_read_len < expected_read)
  {
    read_len = read(sock, recvb + total_read_len, expected_read - total_read_len);  // READ STX
    total_read_len += read_len;
    if (read_len <= 0)
    {
      ROS_ERROR("Read socket failed: %s", strerror(errno));
      result.clear();
      return result;
    }
  }

  std::string recv_header(recvb, read_len);
  // Convert the read len from hex chars to int.
  std::stringstream ss;
  ss << recv_header.substr(1, 4);
  ss >> std::hex >> expected_read;
  ROS_DEBUG_STREAM("Read len " << expected_read);

  // Already read len of 5, take that out.
  uint32_t arr_size = expected_read - 5;
  // Bounds check the size, we really shouldn't exceed 8703 bytes
  // based on the currently known messages on the hokuyo documentations
  if (arr_size > 10000)
  {
    ROS_ERROR("Buffer creation bounds exceeded, shouldn't allocate: %u bytes", arr_size);
    result.clear();
    return result;
  }

  ROS_DEBUG_STREAM("Creating buffer read of arr_Size: " << arr_size);
  // Create buffer space for read.
  boost::shared_array<char> data;
  data.reset(new char[arr_size]);

  // Read the remaining command
  total_read_len = 0;
  read_len = 0;
  expected_read = arr_size;

  ROS_DEBUG_STREAM("Expected body size: " << expected_read);
  while (total_read_len < expected_read)
  {
    read_len = read(sock, data.get()+total_read_len, expected_read - total_read_len);
    total_read_len += read_len;
    ROS_DEBUG_STREAM("Read in after header " << read_len);
    if (read_len <= 0)
    {
      ROS_ERROR("Read socket failed: %s", strerror(errno));
      result.clear();
      return result;
    }
  }

  // Combine the read portions to return for processing.
  result += recv_header;
  result += std::string(data.get(), expected_read);

  // Resume scan after sending.
  if (restart)
  {
    start();
  }

  return result;
}

bool URGCWrapper::isStarted() const
{
  return started_;
}

double URGCWrapper::getRangeMin() const
{
  long minr;
  long maxr;
  urg_distance_min_max(&urg_, &minr, &maxr);
  return static_cast<double>(minr) / 1000.0;
}

double URGCWrapper::getRangeMax() const
{
  long minr;
  long maxr;
  urg_distance_min_max(&urg_, &minr, &maxr);
  return static_cast<double>(maxr) / 1000.0;
}

double URGCWrapper::getAngleMin() const
{
  return urg_step2rad(&urg_, first_step_);
}

double URGCWrapper::getAngleMax() const
{
  return urg_step2rad(&urg_, last_step_);
}

double URGCWrapper::getAngleMinLimit() const
{
  int min_step;
  int max_step;
  urg_step_min_max(&urg_, &min_step, &max_step);
  return urg_step2rad(&urg_, min_step);
}

double URGCWrapper::getAngleMaxLimit() const
{
  int min_step;
  int max_step;
  urg_step_min_max(&urg_, &min_step, &max_step);
  return urg_step2rad(&urg_, max_step);
}

double URGCWrapper::getAngleIncrement() const
{
  double angle_min = getAngleMin();
  double angle_max = getAngleMax();
  return cluster_ * (angle_max - angle_min) / static_cast<double>(last_step_ - first_step_);
}

double URGCWrapper::getScanPeriod() const
{
  long scan_usec = urg_scan_usec(&urg_);
  return 1.e-6 * static_cast<double>(scan_usec);
}

double URGCWrapper::getTimeIncrement() const
{
  int min_step;
  int max_step;
  urg_step_min_max(&urg_, &min_step, &max_step);
  double scan_period = getScanPeriod();
  double circle_fraction = (getAngleMaxLimit() - getAngleMinLimit()) / (2.0 * 3.141592);
  return cluster_ * circle_fraction * scan_period / static_cast<double>(max_step - min_step);
}


std::string URGCWrapper::getIPAddress() const
{
  return ip_address_;
}

int URGCWrapper::getIPPort() const
{
  return ip_port_;
}

std::string URGCWrapper::getSerialPort() const
{
  return serial_port_;
}

int URGCWrapper::getSerialBaud() const
{
  return serial_baud_;
}

std::string URGCWrapper::getVendorName()
{
  return std::string(urg_sensor_vendor(&urg_));
}

std::string URGCWrapper::getProductName()
{
  return std::string(urg_sensor_product_type(&urg_));
}

std::string URGCWrapper::getFirmwareVersion()
{
  return std::string(urg_sensor_firmware_version(&urg_));
}

std::string URGCWrapper::getFirmwareDate()
{
  return std::string(urg_sensor_firmware_date(&urg_));
}

std::string URGCWrapper::getProtocolVersion()
{
  return std::string(urg_sensor_protocol_version(&urg_));
}

std::string URGCWrapper::getDeviceID()
{
  return std::string(urg_sensor_serial_id(&urg_));
}

ros::Duration URGCWrapper::getComputedLatency() const
{
  return system_latency_;
}

ros::Duration URGCWrapper::getUserTimeOffset() const
{
  return user_latency_;
}

std::string URGCWrapper::getSensorStatus()
{
  return std::string(urg_sensor_status(&urg_));
}

std::string URGCWrapper::getSensorState()
{
  return std::string(urg_sensor_state(&urg_));
}

void URGCWrapper::setFrameId(const std::string& frame_id)
{
  frame_id_ = frame_id;
}

void URGCWrapper::setUserLatency(const double latency)
{
  user_latency_.fromSec(latency);
}

// Must be called before urg_start
bool URGCWrapper::setAngleLimitsAndCluster(double& angle_min, double& angle_max, int cluster)
{
  if (started_)
  {
    return false;  // Must not be streaming
  }

  // Set step limits
  first_step_ = urg_rad2step(&urg_, angle_min);
  last_step_ = urg_rad2step(&urg_, angle_max);
  cluster_ = cluster;

  // Make sure step limits are not the same
  if (first_step_ == last_step_)
  {
    // Make sure we're not at a limit
    int min_step;
    int max_step;
    urg_step_min_max(&urg_, &min_step, &max_step);
    if (first_step_ == min_step)  // At beginning of range
    {
      last_step_ = first_step_ + 1;
    }
    else     // At end of range (or all other cases)
    {
      first_step_ = last_step_ - 1;
    }
  }

  // Make sure angle_max is greater than angle_min (should check this after end limits)
  if (last_step_ < first_step_)
  {
    double temp = first_step_;
    first_step_ = last_step_;
    last_step_ = temp;
  }

  angle_min = urg_step2rad(&urg_, first_step_);
  angle_max = urg_step2rad(&urg_, last_step_);
  int result = urg_set_scanning_parameter(&urg_, first_step_, last_step_, cluster);
  if (result < 0)
  {
    return false;
  }
  return true;
}

bool URGCWrapper::setSkip(int skip)
{
  skip_ = skip;
}

bool URGCWrapper::isIntensitySupported()
{
  if (started_)
  {
    return false;  // Must not be streaming
  }

  urg_start_measurement(&urg_, URG_DISTANCE_INTENSITY, 0, 0);
  int ret = urg_get_distance_intensity(&urg_, &data_[0], &intensity_[0], NULL, NULL);
  if (ret <= 0)
  {
    return false;  // Failed to start measurement with intensity: must not support it
  }
  urg_stop_measurement(&urg_);
  return true;
}

bool URGCWrapper::isMultiEchoSupported()
{
  if (started_)
  {
    return false;  // Must not be streaming
  }

  urg_start_measurement(&urg_, URG_MULTIECHO, 0, 0);
  int ret = urg_get_multiecho(&urg_, &data_[0], NULL, NULL);
  if (ret <= 0)
  {
    return false;  // Failed to start measurement with multiecho: must not support it
  }
  urg_stop_measurement(&urg_);
  return true;
}

ros::Duration URGCWrapper::getAngularTimeOffset() const
{
  // Adjust value for Hokuyo's timestamps
  // Hokuyo's timestamps start from the rear center of the device (at Pi according to ROS standards)
  double circle_fraction = 0.0;
  if (first_step_ == 0 && last_step_ == 0)
  {
    circle_fraction = (getAngleMinLimit() + 3.141592) / (2.0 * 3.141592);
  }
  else
  {
    circle_fraction = (getAngleMin() + 3.141592) / (2.0 * 3.141592);
  }
  return ros::Duration(circle_fraction * getScanPeriod());
}

ros::Duration URGCWrapper::computeLatency(size_t num_measurements)
{
  system_latency_.fromNSec(0);

  ros::Duration start_offset = getNativeClockOffset(1);
  ros::Duration previous_offset;

  std::vector<ros::Duration> time_offsets(num_measurements);
  for (size_t i = 0; i < num_measurements; i++)
  {
    ros::Duration scan_offset = getTimeStampOffset(1);
    ros::Duration post_offset = getNativeClockOffset(1);
    ros::Duration adjusted_scan_offset = scan_offset - start_offset;
    ros::Duration adjusted_post_offset = post_offset - start_offset;
    ros::Duration average_offset;
    average_offset.fromSec((adjusted_post_offset.toSec() + previous_offset.toSec()) / 2.0);

    time_offsets[i] = adjusted_scan_offset - average_offset;

    previous_offset = adjusted_post_offset;
  }

  // Get median value
  // Sort vector using nth_element (partially sorts up to the median index)
  std::nth_element(time_offsets.begin(), time_offsets.begin() + time_offsets.size() / 2, time_offsets.end());
  system_latency_ = time_offsets[time_offsets.size() / 2];
  // Angular time offset makes the output comparable to that of hokuyo_node
  return system_latency_ + getAngularTimeOffset();
}

ros::Duration URGCWrapper::getNativeClockOffset(size_t num_measurements)
{
  if (started_)
  {
    std::stringstream ss;
    ss << "Cannot get native clock offset while started.";
    throw std::runtime_error(ss.str());
  }

  if (urg_start_time_stamp_mode(&urg_) < 0)
  {
    std::stringstream ss;
    ss << "Cannot start time stamp mode.";
    throw std::runtime_error(ss.str());
  }

  std::vector<ros::Duration> time_offsets(num_measurements);
  for (size_t i = 0; i < num_measurements; i++)
  {
    ros::Time request_time = ros::Time::now();
    ros::Time laser_time;
    laser_time.fromNSec(1e6 * (uint64_t)urg_time_stamp(&urg_));  // 1e6 * milliseconds = nanoseconds
    ros::Time response_time = ros::Time::now();
    ros::Time average_time;
    average_time.fromSec((response_time.toSec() + request_time.toSec()) / 2.0);
    time_offsets[i] = laser_time - average_time;
  }

  if (urg_stop_time_stamp_mode(&urg_) < 0)
  {
    std::stringstream ss;
    ss << "Cannot stop time stamp mode.";
    throw std::runtime_error(ss.str());
  };

  // Return median value
  // Sort vector using nth_element (partially sorts up to the median index)
  std::nth_element(time_offsets.begin(), time_offsets.begin() + time_offsets.size() / 2, time_offsets.end());
  return time_offsets[time_offsets.size() / 2];
}

ros::Duration URGCWrapper::getTimeStampOffset(size_t num_measurements)
{
  if (started_)
  {
    std::stringstream ss;
    ss << "Cannot get time stamp offset while started.";
    throw std::runtime_error(ss.str());
  }

  start();

  std::vector<ros::Duration> time_offsets(num_measurements);
  for (size_t i = 0; i < num_measurements; i++)
  {
    long time_stamp;
    unsigned long long system_time_stamp;
    int ret = 0;

    if (measurement_type_ == URG_DISTANCE)
    {
      ret = urg_get_distance(&urg_, &data_[0], &time_stamp, &system_time_stamp);
    }
    else if (measurement_type_ == URG_DISTANCE_INTENSITY)
    {
      ret = urg_get_distance_intensity(&urg_, &data_[0], &intensity_[0], &time_stamp, &system_time_stamp);
    }
    else if (measurement_type_ == URG_MULTIECHO)
    {
      ret = urg_get_multiecho(&urg_, &data_[0], &time_stamp, &system_time_stamp);
    }
    else if (measurement_type_ == URG_MULTIECHO_INTENSITY)
    {
      ret = urg_get_multiecho_intensity(&urg_, &data_[0], &intensity_[0], &time_stamp, &system_time_stamp);
    }

    if (ret <= 0)
    {
      std::stringstream ss;
      ss << "Cannot get scan to measure time stamp offset.";
      throw std::runtime_error(ss.str());
    }

    ros::Time laser_timestamp;
    laser_timestamp.fromNSec(1e6 * (uint64_t)time_stamp);
    ros::Time system_time;
    system_time.fromNSec((uint64_t)system_time_stamp);

    time_offsets[i] = laser_timestamp - system_time;
  }

  stop();

  // Return median value
  // Sort vector using nth_element (partially sorts up to the median index)
  std::nth_element(time_offsets.begin(), time_offsets.begin() + time_offsets.size() / 2, time_offsets.end());
  return time_offsets[time_offsets.size() / 2];
}
}  // namespace urg_node