mirror of https://github.com/ArduPilot/ardupilot
87 lines
2.8 KiB
C++
87 lines
2.8 KiB
C++
/*
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SITL handling
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This simulates an analog airspeed sensor
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Andrew Tridgell November 2011
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*/
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#include <AP_HAL/AP_HAL.h>
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#if CONFIG_HAL_BOARD == HAL_BOARD_SITL && !defined(HAL_BUILD_AP_PERIPH)
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#include "AP_HAL_SITL.h"
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#include "AP_HAL_SITL_Namespace.h"
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#include "HAL_SITL_Class.h"
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#include "SITL_State.h"
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#include <SITL/SITL.h>
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#include <AP_Math/AP_Math.h>
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extern const AP_HAL::HAL& hal;
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using namespace HALSITL;
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// return current scale factor that converts from equivalent to true airspeed
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// valid for altitudes up to 10km AMSL
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// assumes standard atmosphere lapse rate
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static float get_EAS2TAS(float altitude)
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{
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float pressure = AP::baro().get_pressure();
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if (is_zero(pressure)) {
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return 1.0f;
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}
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float sigma, delta, theta;
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AP_Baro::SimpleAtmosphere(altitude * 0.001, sigma, delta, theta);
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float tempK = C_TO_KELVIN(25) - ISA_LAPSE_RATE * altitude;
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const float eas2tas_squared = SSL_AIR_DENSITY / (pressure / (ISA_GAS_CONSTANT * tempK));
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if (!is_positive(eas2tas_squared)) {
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return 1.0;
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}
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return sqrtf(eas2tas_squared);
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}
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/*
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convert airspeed in m/s to an airspeed sensor value
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*/
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void SITL_State::_update_airspeed(float true_airspeed)
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{
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for (uint8_t i=0; i<AIRSPEED_MAX_SENSORS; i++) {
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const auto &arspd = _sitl->airspeed[i];
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float airspeed = true_airspeed / get_EAS2TAS(_sitl->state.altitude);
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const float diff_pressure = sq(airspeed) / arspd.ratio;
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float airspeed_raw;
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// apply noise to the differential pressure. This emulates the way
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// airspeed noise reduces with speed
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airspeed = sqrtf(fabsf(arspd.ratio*(diff_pressure + arspd.noise * rand_float())));
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// check sensor failure
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if (is_positive(arspd.fail)) {
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airspeed = arspd.fail;
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}
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if (!is_zero(arspd.fail_pressure)) {
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// compute a realistic pressure report given some level of trapper air pressure in the tube and our current altitude
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// algorithm taken from https://en.wikipedia.org/wiki/Calibrated_airspeed#Calculation_from_impact_pressure
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float tube_pressure = fabsf(arspd.fail_pressure - AP::baro().get_pressure() + arspd.fail_pitot_pressure);
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airspeed = 340.29409348 * sqrt(5 * (pow((tube_pressure / SSL_AIR_PRESSURE + 1), 2.0/7.0) - 1.0));
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}
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float airspeed_pressure = (airspeed * airspeed) / arspd.ratio;
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// flip sign here for simulating reversed pitot/static connections
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if (arspd.signflip) {
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airspeed_pressure *= -1;
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}
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// apply airspeed sensor offset in m/s
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airspeed_raw = airspeed_pressure + arspd.offset;
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_sitl->state.airspeed_raw_pressure[i] = airspeed_pressure;
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airspeed_pin_value[i] = MIN(0xFFFF, airspeed_raw / 4);
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}
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}
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#endif
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