地形跟随/保持和范围辅助
PX4支持地形跟随和地形保持在位置和海拔模式，在multicopters和垂直起降车辆MC模式有一个距离传感器。
PX4还支持在任何模式下（无论何时何地）还是在低速低空飞行时（距离辅助）将距离传感器用作高度数据的主要来源。
PX4不“本地”支持任务中的地形跟随。QGroundControl可用于定义大致遵循地形的任务（这只是根据地形上方的高度（从地图数据库获取航点处的地形高度）来设置航点高度）。
地形跟随
地形跟踪使车辆在低海拔行驶时能够自动保持高于地面的相对恒定高度。这有助于避免障碍物并在变化的地形上飞行时保持恒定的高度（例如，用于航空摄影）。
当地形跟踪被使能，PX4使用EKF估计器的输出，以提供海拔估计和估计的地形高度，以提供高度的设定点（使用另一估计器从距离传感器测量值计算）。随着距地面的距离的变化，海拔设定点会进行调整，以使地面上方的高度保持恒定。
At higher altitudes (when the estimator reports that the distance sensor data is invalid) the vehicle switches toaltitude following, and will typically fly at a near-constant height above mean sea level (AMSL) using the barometer for altitude data.
More precisely, the vehicle will use the_primary source of altitude data_as defined inEKF2_HGT_MODE. This is, by default, the barometer.
Terrain following is enabled by settingMPC_ALT_MODEto1.
Terrain Hold
_Terrain hold_uses a distance sensor to help a vehicle to better maintain a constant height above ground in altitude control modes, when horizontally stationary at low altitude. This allows a vehicle to avoid altitude changes due to barometer drift or excessive barometer interference from rotor wash.
This feature can be enabled inPositionandAltitude modes, on_multicopters_and_VTOL vehicles in MC mode_that have adistance sensor.
When moving horizontally (speed >MPC_HOLD_MAX_XY), or above the altitude where the distance sensor is providing valid data, the vehicle will switch intoaltitude following.
Terrain holding is enabled by settingMPC_ALT_MODEto2.
_Terrain hold_is implemented similarly toterrain following. It uses the output of the EKF estimator to provide the altitude estimate, and the estimated terrain altitude (calculated from distance sensor measurements using a separate, single state terrain estimator) to provide the altitude setpoint. If the distance to ground changes due to external forces, the altitude setpoint adjusts to keep the height above ground constant.
Distance Sensor as Primary Source of Height
PX4 allows you to make a distance sensor theprimary source of altitude data(in any flight mode/vehicle type). This may be useful when no barometer is available, or for applications when the vehicle is_guaranteed_to only fly over a near-flat surface (e.g. indoors).
The default and preferred altitude sensor for most use cases is the barometer (when available).
When using a distance sensor as the primary source of height, fliers should be aware:
- Flying over obstacles can lead to the estimator rejecting rangefinder data (due to internal data consistency checks), which can result in poor altitude holding while the estimator is relying purely on accelerometer estimates.
This scenario might occur when a vehicle ascends a slope at a near-constant height above ground, because the rangefinder altitude does not change while that estimated from the accelerometer does.
The ECL performs innovation consistency checks that take into account the error between measurement and current state as well as the estimated variance of the state and the variance of the measurement itself. If the checks fail the rangefinder data will be rejected, and the altitude will be estimated from the accelerometer. After 5 seconds of inconsistent data the estimator resets the state (in this case height) to match the current distance sensor data. The measurements might also become consistent again, for example, if the vehicle descends, or if the estimated height drifts to match the measured rangefinder height. - The local NED origin will move up and down with ground level.
- Rangefinder performance over uneven surfaces (e.g. trees) can be very poor, resulting in noisy and inconsistent data. This again leads to poor altitude hold.
The feature is enabled by setting:EKF2_HGT_MODE=2.
Range Aid
Range Aid_uses a distance sensor as the primary source of height estimation during low speed/low altitude operation, but will otherwise use the primary source of altitude data defined inEKF2_HGT_MODE(typically a barometer). It is primarily intended for_takeoff and landing, in cases where the barometer setup is such that interference from rotor wash is excessive and can corrupt EKF state estimates.
Range aid may also be used to improve altitude hold when the vehicle is stationary.
Terrain Holdis recommended over_Range Aid_for terrain holding. This is because terrain hold uses the normal ECL/EKF estimator for determining height, and this is generally more reliable than a distance sensor in most conditions.
_Range Aid_is enabled by settingEKF2_RNG_AID=1(when the primary source of altitude data (EKF2_HGT_MODE) is_not_the rangefinder).
Range aid is further configured using theEKF2_RNG_A_parameters:
- EKF2_RNG_A_VMAX : Maximum horizontal speed, above which range aid is disabled.
- EKF2_RNG_A_HMAX : Maximum height, above which range aid is disabled.
- EKF2_RNG_A_IGATE ：范围辅助功能一致性检查“门”（在禁用范围辅助功能之前的错误度量）。