ardupilot/libraries/AP_Landing/AP_Landing_Slope.cpp

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/*
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/>.
*/
/*
* AP_Landing_Slope.cpp - Landing logic handler for ArduPlane for STANDARD_GLIDE_SLOPE
*/
#include "AP_Landing.h"
#include <GCS_MAVLink/GCS.h>
#include <AP_HAL/AP_HAL.h>
void AP_Landing::type_slope_do_land(const AP_Mission::Mission_Command& cmd, const float relative_altitude)
{
initial_slope = 0;
slope = 0;
// once landed, post some landing statistics to the GCS
type_slope_flags.post_stats = false;
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type_slope_stage = SLOPE_STAGE_NORMAL;
gcs().send_text(MAV_SEVERITY_INFO, "Landing approach start at %.1fm", (double)relative_altitude);
}
void AP_Landing::type_slope_verify_abort_landing(const Location &prev_WP_loc, Location &next_WP_loc, bool &throttle_suppressed)
{
// when aborting a landing, mimic the verify_takeoff with steering hold. Once
// the altitude has been reached, restart the landing sequence
throttle_suppressed = false;
nav_controller->update_heading_hold(get_bearing_cd(prev_WP_loc, next_WP_loc));
}
/*
update navigation for landing. Called when on landing approach or
final flare
*/
bool AP_Landing::type_slope_verify_land(const Location &prev_WP_loc, Location &next_WP_loc, const Location &current_loc,
const float height, const float sink_rate, const float wp_proportion, const uint32_t last_flying_ms, const bool is_armed, const bool is_flying, const bool rangefinder_state_in_range)
{
// we don't 'verify' landing in the sense that it never completes,
// so we don't verify command completion. Instead we use this to
// adjust final landing parameters
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// determine stage
if (type_slope_stage == SLOPE_STAGE_NORMAL) {
const bool heading_lined_up = abs(nav_controller->bearing_error_cd()) < 1000 && !nav_controller->data_is_stale();
const bool on_flight_line = fabsf(nav_controller->crosstrack_error()) < 5.0f && !nav_controller->data_is_stale();
const bool below_prev_WP = current_loc.alt < prev_WP_loc.alt;
if ((mission.get_prev_nav_cmd_id() == MAV_CMD_NAV_LOITER_TO_ALT) ||
(wp_proportion >= 0 && heading_lined_up && on_flight_line) ||
(wp_proportion > 0.15f && heading_lined_up && below_prev_WP) ||
(wp_proportion > 0.5f)) {
type_slope_stage = SLOPE_STAGE_APPROACH;
}
}
/* Set land_complete (which starts the flare) under 3 conditions:
1) we are within LAND_FLARE_ALT meters of the landing altitude
2) we are within LAND_FLARE_SEC of the landing point vertically
by the calculated sink rate (if LAND_FLARE_SEC != 0)
3) we have gone past the landing point and don't have
rangefinder data (to prevent us keeping throttle on
after landing if we've had positive baro drift)
*/
// flare check:
// 1) below flare alt/sec requires approach stage check because if sec/alt are set too
// large, and we're on a hard turn to line up for approach, we'll prematurely flare by
// skipping approach phase and the extreme roll limits will make it hard to line up with runway
// 2) passed land point and don't have an accurate AGL
// 3) probably crashed (ensures motor gets turned off)
const bool on_approach_stage = type_slope_is_on_approach();
const bool below_flare_alt = (height <= flare_alt);
const bool below_flare_sec = (flare_sec > 0 && height <= sink_rate * flare_sec);
const bool probably_crashed = (aparm.crash_detection_enable && fabsf(sink_rate) < 0.2f && !is_flying);
if ((on_approach_stage && below_flare_alt) ||
(on_approach_stage && below_flare_sec && (wp_proportion > 0.5)) ||
(!rangefinder_state_in_range && wp_proportion >= 1) ||
probably_crashed) {
if (type_slope_stage != SLOPE_STAGE_FINAL) {
type_slope_flags.post_stats = true;
if (is_flying && (AP_HAL::millis()-last_flying_ms) > 3000) {
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gcs().send_text(MAV_SEVERITY_CRITICAL, "Flare crash detected: speed=%.1f", (double)AP::gps().ground_speed());
} else {
gcs().send_text(MAV_SEVERITY_INFO, "Flare %.1fm sink=%.2f speed=%.1f dist=%.1f",
(double)height, (double)sink_rate,
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(double)AP::gps().ground_speed(),
(double)get_distance(current_loc, next_WP_loc));
}
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type_slope_stage = SLOPE_STAGE_FINAL;
}
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if (AP::gps().ground_speed() < 3) {
// reload any airspeed or groundspeed parameters that may have
// been set for landing. We don't do this till ground
// speed drops below 3.0 m/s as otherwise we will change
// target speeds too early.
aparm.airspeed_cruise_cm.load();
aparm.min_gndspeed_cm.load();
aparm.throttle_cruise.load();
}
} else if (type_slope_stage == SLOPE_STAGE_APPROACH && pre_flare_airspeed > 0) {
bool reached_pre_flare_alt = pre_flare_alt > 0 && (height <= pre_flare_alt);
bool reached_pre_flare_sec = pre_flare_sec > 0 && (height <= sink_rate * pre_flare_sec);
if (reached_pre_flare_alt || reached_pre_flare_sec) {
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type_slope_stage = SLOPE_STAGE_PREFLARE;
}
}
/*
when landing we keep the L1 navigation waypoint 200m ahead. This
prevents sudden turns if we overshoot the landing point
*/
struct Location land_WP_loc = next_WP_loc;
int32_t land_bearing_cd = get_bearing_cd(prev_WP_loc, next_WP_loc);
location_update(land_WP_loc,
land_bearing_cd*0.01f,
get_distance(prev_WP_loc, current_loc) + 200);
nav_controller->update_waypoint(prev_WP_loc, land_WP_loc);
// once landed and stationary, post some statistics
// this is done before disarm_if_autoland_complete() so that it happens on the next loop after the disarm
if (type_slope_flags.post_stats && !is_armed) {
type_slope_flags.post_stats = false;
gcs().send_text(MAV_SEVERITY_INFO, "Distance from LAND point=%.2fm", (double)get_distance(current_loc, next_WP_loc));
}
// check if we should auto-disarm after a confirmed landing
if (type_slope_stage == SLOPE_STAGE_FINAL) {
disarm_if_autoland_complete_fn();
}
/*
we return false as a landing mission item never completes
we stay on this waypoint unless the GCS commands us to change
mission item, reset the mission, command a go-around or finish
a land_abort procedure.
*/
return false;
}
void AP_Landing::type_slope_adjust_landing_slope_for_rangefinder_bump(AP_Vehicle::FixedWing::Rangefinder_State &rangefinder_state, Location &prev_WP_loc, Location &next_WP_loc, const Location &current_loc, const float wp_distance, int32_t &target_altitude_offset_cm)
{
// check the rangefinder correction for a large change. When found, recalculate the glide slope. This is done by
// determining the slope from your current location to the land point then following that back up to the approach
// altitude and moving the prev_wp to that location. From there
float correction_delta = fabsf(rangefinder_state.last_stable_correction) - fabsf(rangefinder_state.correction);
if (slope_recalc_shallow_threshold <= 0 ||
fabsf(correction_delta) < slope_recalc_shallow_threshold) {
return;
}
rangefinder_state.last_stable_correction = rangefinder_state.correction;
float corrected_alt_m = (adjusted_altitude_cm_fn() - next_WP_loc.alt)*0.01f - rangefinder_state.correction;
float total_distance_m = get_distance(prev_WP_loc, next_WP_loc);
float top_of_glide_slope_alt_m = total_distance_m * corrected_alt_m / wp_distance;
prev_WP_loc.alt = top_of_glide_slope_alt_m*100 + next_WP_loc.alt;
// re-calculate auto_state.land_slope with updated prev_WP_loc
setup_landing_glide_slope(prev_WP_loc, next_WP_loc, current_loc, target_altitude_offset_cm);
if (rangefinder_state.correction >= 0) { // we're too low or object is below us
// correction positive means we're too low so we should continue on with
// the newly computed shallower slope instead of pitching/throttling up
} else if (slope_recalc_steep_threshold_to_abort > 0 && !type_slope_flags.has_aborted_due_to_slope_recalc) {
// correction negative means we're too high and need to point down (and speed up) to re-align
// to land on target. A large negative correction means we would have to dive down a lot and will
// generating way too much speed that we can not bleed off in time. It is better to remember
// the large baro altitude offset and abort the landing to come around again with the correct altitude
// offset and "perfect" slope.
// calculate projected slope with projected alt
float new_slope_deg = degrees(atan(slope));
float initial_slope_deg = degrees(atan(initial_slope));
// is projected slope too steep?
if (new_slope_deg - initial_slope_deg > slope_recalc_steep_threshold_to_abort) {
gcs().send_text(MAV_SEVERITY_INFO, "Landing slope too steep, aborting (%.0fm %.1fdeg)",
(double)rangefinder_state.correction, (double)(new_slope_deg - initial_slope_deg));
alt_offset = rangefinder_state.correction;
flags.commanded_go_around = true;
type_slope_flags.has_aborted_due_to_slope_recalc = true; // only allow this once.
log();
}
}
}
bool AP_Landing::type_slope_request_go_around(void)
{
flags.commanded_go_around = true;
return true;
}
/*
a special glide slope calculation for the landing approach
During the land approach use a linear glide slope to a point
projected through the landing point. We don't use the landing point
itself as that leads to discontinuities close to the landing point,
which can lead to erratic pitch control
*/
void AP_Landing::type_slope_setup_landing_glide_slope(const Location &prev_WP_loc, const Location &next_WP_loc, const Location &current_loc, int32_t &target_altitude_offset_cm)
{
float total_distance = get_distance(prev_WP_loc, next_WP_loc);
// If someone mistakenly puts all 0's in their LAND command then total_distance
// will be calculated as 0 and cause a divide by 0 error below. Lets avoid that.
if (total_distance < 1) {
total_distance = 1;
}
// height we need to sink for this WP
float sink_height = (prev_WP_loc.alt - next_WP_loc.alt)*0.01f;
// current ground speed
float groundspeed = ahrs.groundspeed();
if (groundspeed < 0.5f) {
groundspeed = 0.5f;
}
// calculate time to lose the needed altitude
float sink_time = total_distance / groundspeed;
if (sink_time < 0.5f) {
sink_time = 0.5f;
}
// find the sink rate needed for the target location
float sink_rate = sink_height / sink_time;
// the height we aim for is the one to give us the right flare point
float aim_height = flare_sec * sink_rate;
if (aim_height <= 0) {
aim_height = flare_alt;
}
// don't allow the aim height to be too far above LAND_FLARE_ALT
if (flare_alt > 0 && aim_height > flare_alt*2) {
aim_height = flare_alt*2;
}
// calculate slope to landing point
bool is_first_calc = is_zero(slope);
slope = (sink_height - aim_height) / total_distance;
if (is_first_calc) {
gcs().send_text(MAV_SEVERITY_INFO, "Landing glide slope %.1f degrees", (double)degrees(atanf(slope)));
}
// time before landing that we will flare
float flare_time = aim_height / SpdHgt_Controller->get_land_sinkrate();
// distance to flare is based on ground speed, adjusted as we
// get closer. This takes into account the wind
float flare_distance = groundspeed * flare_time;
// don't allow the flare before half way along the final leg
if (flare_distance > total_distance/2) {
flare_distance = total_distance/2;
}
// project a point 500 meters past the landing point, passing
// through the landing point
const float land_projection = 500;
int32_t land_bearing_cd = get_bearing_cd(prev_WP_loc, next_WP_loc);
// now calculate our aim point, which is before the landing
// point and above it
Location loc = next_WP_loc;
location_update(loc, land_bearing_cd*0.01f, -flare_distance);
loc.alt += aim_height*100;
// calculate point along that slope 500m ahead
location_update(loc, land_bearing_cd*0.01f, land_projection);
loc.alt -= slope * land_projection * 100;
// setup the offset_cm for set_target_altitude_proportion()
target_altitude_offset_cm = loc.alt - prev_WP_loc.alt;
// calculate the proportion we are to the target
float land_proportion = location_path_proportion(current_loc, prev_WP_loc, loc);
// now setup the glide slope for landing
set_target_altitude_proportion_fn(loc, 1.0f - land_proportion);
// stay within the range of the start and end locations in altitude
constrain_target_altitude_location_fn(loc, prev_WP_loc);
}
int32_t AP_Landing::type_slope_get_target_airspeed_cm(void) {
// we're landing, check for custom approach and
// pre-flare airspeeds. Also increase for head-winds
const float land_airspeed = SpdHgt_Controller->get_land_airspeed();
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int32_t target_airspeed_cm = aparm.airspeed_cruise_cm;
switch (type_slope_stage) {
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case SLOPE_STAGE_APPROACH:
if (land_airspeed >= 0) {
target_airspeed_cm = land_airspeed * 100;
}
break;
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case SLOPE_STAGE_PREFLARE:
case SLOPE_STAGE_FINAL:
if (pre_flare_airspeed > 0) {
// if we just preflared then continue using the pre-flare airspeed during final flare
target_airspeed_cm = pre_flare_airspeed * 100;
} else if (land_airspeed >= 0) {
target_airspeed_cm = land_airspeed * 100;
}
break;
default:
break;
}
// when landing, add half of head-wind.
const int32_t head_wind_compensation_cm = head_wind() * 0.5f * 100;
// Do not lower it or exceed cruise speed
return constrain_int32(target_airspeed_cm + head_wind_compensation_cm, target_airspeed_cm, aparm.airspeed_cruise_cm);
}
int32_t AP_Landing::type_slope_constrain_roll(const int32_t desired_roll_cd, const int32_t level_roll_limit_cd) {
if (type_slope_stage == SLOPE_STAGE_FINAL) {
return constrain_int32(desired_roll_cd, level_roll_limit_cd * -1, level_roll_limit_cd);
} else {
return desired_roll_cd;
}
}
bool AP_Landing::type_slope_is_flaring(void) const
{
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return (type_slope_stage == SLOPE_STAGE_FINAL);
}
bool AP_Landing::type_slope_is_on_approach(void) const
{
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return (type_slope_stage == SLOPE_STAGE_APPROACH ||
type_slope_stage == SLOPE_STAGE_PREFLARE);
}
bool AP_Landing::type_slope_is_expecting_impact(void) const
{
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return (type_slope_stage == SLOPE_STAGE_PREFLARE ||
type_slope_stage == SLOPE_STAGE_FINAL);
}
bool AP_Landing::type_slope_is_complete(void) const
{
return (type_slope_stage == SLOPE_STAGE_FINAL);
}
void AP_Landing::type_slope_log(void) const
{
// log to DataFlash
DataFlash_Class::instance()->Log_Write("LAND", "TimeUS,stage,f1,f2,slope,slopeInit,altO", "QBBBfff",
AP_HAL::micros64(),
type_slope_stage,
flags,
type_slope_flags,
(double)slope,
(double)initial_slope,
(double)alt_offset);
}
bool AP_Landing::type_slope_is_throttle_suppressed(void) const
{
return type_slope_stage == SLOPE_STAGE_FINAL;
}