px4flow.c

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/*
 * Copyright (C) 2013 Gautier Hattenberger
 * 2016 Michal Podhradsky <michal.podhradsky@aggiemail.usu.edu>
 *
 * This file is part of paparazzi.
 *
 * paparazzi is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * paparazzi is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with paparazzi; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 */
 
#include "modules/optical_flow/px4flow.h"
#include "modules/datalink/mavlink_decoder.h"
#include "subsystems/abi.h"
 
// State interface for rotation compensation
#include "state.h"
 
// Messages
#include "mcu_periph/uart.h"
#include "pprzlink/messages.h"
#include "subsystems/datalink/downlink.h"
 
struct mavlink_heartbeat heartbeat;
struct mavlink_optical_flow optical_flow;
struct mavlink_optical_flow_rad optical_flow_rad;
 
// message ID in Mavlink (v1.0)
#define MAVLINK_OPTICAL_HEARTBEAT_MSG_ID 0
#define MAVLINK_OPTICAL_FLOW_MSG_ID 100
#define MAVLINK_OPTICAL_FLOW_RAD_MSG_ID 106
 
/*
 * acceptable quality of optical flow (0-min,1-max)
 * higher threshold means fewer measurements will be available
 * but they will be more precise. Generally it is probably a better
 * idea to have lower threshold, and propagate the noise (1-quality)
 * to the INS
 */
#ifndef PX4FLOW_QUALITY_THRESHOLD
#define PX4FLOW_QUALITY_THRESHOLD 0.1
#endif
 
// request structs for mavlink decoder
struct mavlink_msg_req req_flow;
struct mavlink_msg_req req_flow_rad;
struct mavlink_msg_req req_heartbeat;
 
// enable/disable AGL updates
bool px4flow_update_agl;
 
// compensate AGL for body rotation
bool px4flow_compensate_rotation;
 
// standard deviation of the measurement
float px4flow_stddev;
 
 
// callback function on message reception
static void decode_optical_flow_msg(struct mavlink_message *msg __attribute__((unused)))
{
  static float quality = 0;
  static float noise = 0;
  uint32_t now_ts = get_sys_time_usec();
  quality = ((float)optical_flow.quality) / 255.0;
  noise = px4flow_stddev + (1 - quality) * px4flow_stddev * 10;
  noise = noise * noise; // square the noise to get variance of the measurement
 
  if (quality > PX4FLOW_QUALITY_THRESHOLD) {
    // flip the axis (if the PX4FLOW is mounted as shown in
    // https://pixhawk.org/modules/px4flow
    AbiSendMsgVELOCITY_ESTIMATE(VEL_PX4FLOW_ID,
                                optical_flow.time_usec,
                                optical_flow.flow_comp_m_y,
                                optical_flow.flow_comp_m_x,
                                0.0f,
                                noise,
                                noise,
                                -1.f);
  }
 
  // compensate AGL measurement for body rotation
  if (px4flow_compensate_rotation) {
      float phi = stateGetNedToBodyEulers_f()->phi;
      float theta = stateGetNedToBodyEulers_f()->theta;
      float gain = (float)fabs( (double) (cosf(phi) * cosf(theta)));
      optical_flow.ground_distance = optical_flow.ground_distance / gain;
  }
 
  if (px4flow_update_agl) {
    // positive distance means it's known/valid
    if (optical_flow.ground_distance > 0) {
      AbiSendMsgAGL(AGL_SONAR_PX4FLOW_ID, now_ts, optical_flow.ground_distance);
    }
  }
}
 
static void decode_optical_flow_rad_msg(struct mavlink_message *msg __attribute__((unused)))
{
  // TODO: do something useful with the data here
}
 
static void decode_heartbeat_msg(struct mavlink_message *msg __attribute__((unused)))
{
  //TODO: Check whether we have a right version of firmware etc? i.e. heartbeat.autopilot=MAV_AUTOPILOT_PX4
}
 
void px4flow_init(void)
{
  // register mavlink messages
  req_flow.msg_id = MAVLINK_OPTICAL_FLOW_MSG_ID;
  req_flow.callback = decode_optical_flow_msg;
  req_flow.msg.payload = (uint8_t *)(&optical_flow);
  mavlink_register_msg(&mavlink_tp, &req_flow);
 
  req_flow_rad.msg_id = MAVLINK_OPTICAL_FLOW_RAD_MSG_ID;
  req_flow_rad.callback = decode_optical_flow_rad_msg;
  req_flow_rad.msg.payload = (uint8_t *)(&optical_flow_rad);
  mavlink_register_msg(&mavlink_tp, &req_flow_rad);
 
  req_heartbeat.msg_id = MAVLINK_OPTICAL_HEARTBEAT_MSG_ID;
  req_heartbeat.callback = decode_heartbeat_msg;
  req_heartbeat.msg.payload = (uint8_t *)(&heartbeat);
  mavlink_register_msg(&mavlink_tp, &req_heartbeat);
 
  px4flow_update_agl = USE_PX4FLOW_AGL;
  px4flow_compensate_rotation = PX4FLOW_COMPENSATE_ROTATION;
  px4flow_stddev = PX4FLOW_NOISE_STDDEV;
}
 
 
void px4flow_downlink(void)
{
  static float timestamp = 0;
  static uint8_t distance_quality = 0;
  timestamp = ((float)optical_flow.time_usec) * 0.000001;
  DOWNLINK_SEND_OPTICAL_FLOW(DefaultChannel, DefaultDevice,
                            &timestamp,
                            &optical_flow.sensor_id,
                            &optical_flow.flow_x,
                            &optical_flow.flow_y,
                            &optical_flow.flow_comp_m_x,
                            &optical_flow.flow_comp_m_y,
                            &optical_flow.quality,
                            &optical_flow.ground_distance,
                            &distance_quality);
}