ardupilot/libraries/AP_Proximity/AP_Proximity_Backend.cpp

/*
   This program 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 3 of the License, or
   (at your option) any later version.

   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <AP_Common/AP_Common.h>
#include <AP_HAL/AP_HAL.h>
#include "AP_Proximity.h"
#include "AP_Proximity_Backend.h"

/*
  base class constructor. 
  This incorporates initialisation as well.
*/
AP_Proximity_Backend::AP_Proximity_Backend(AP_Proximity &_frontend, AP_Proximity::Proximity_State &_state) :
        frontend(_frontend),
        state(_state)
{
}

// get distance in meters in a particular direction in degrees (0 is forward, angles increase in the clockwise direction)
bool AP_Proximity_Backend::get_horizontal_distance(float angle_deg, float &distance) const
{
    uint8_t sector;
    if (convert_angle_to_sector(angle_deg, sector)) {
        if (_distance_valid[sector]) {
            distance = _distance[sector];
            return true;
        }
    }
    return false;
}

// set status and update valid count
void AP_Proximity_Backend::set_status(AP_Proximity::Proximity_Status status)
{
    state.status = status;
}

bool AP_Proximity_Backend::convert_angle_to_sector(float angle_degrees, uint8_t &sector) const
{
    // sanity check angle
    if (angle_degrees > 360.0f || angle_degrees < -180.0f) {
        return false;
    }

    // convert to 0 ~ 360
    if (angle_degrees < 0.0f) {
        angle_degrees += 360.0f;
    }

    bool closest_found = false;
    uint8_t closest_sector;
    float closest_angle;

    // search for which sector angle_degrees falls into
    for (uint8_t i = 0; i < _num_sectors; i++) {
        float angle_diff = fabsf(wrap_180(_sector_middle_deg[i] - angle_degrees));

        // record if closest
        if (!closest_found || angle_diff < closest_angle) {
            closest_found = true;
            closest_sector = i;
            closest_angle = angle_diff;
        }

        if (fabsf(angle_diff) <= _sector_width_deg[i] / 2.0f) {
            sector = i;
            return true;
        }
    }

    // angle_degrees might have been within a gap between sectors
    if (closest_found) {
        sector = closest_sector;
        return true;
    }

    return false;
}