Filter Aiding Measurements
Internal aiding measurements are enabled and disabled by the Aiding Measurement Control (0x0D,0x50) command. External aiding measurements are input to the device via the Aiding Descriptor Set (0x13) commands.
Internal Aiding Sensors
Magnetometer AidingA measurement of the local magnetic field in conjunction with a location dependent model of Earth's magnetic field can be used for heading aiding. Special care must be taken when using this method. See Magnetometer Warning for details. This aiding measurement can only be sourced internally.
Altimeter Aiding
Altimeter aiding can help stabilize altitude in challenging GNSS environments. It can be sourced internally through the 3DM-CV7's pressure altimeter
External Aiding Measurements
The 3DM-CV7-INS has been designed to allow users to easily configure and provide external aiding measurements that improve state estimation in challenging GNSS conditions.
Note: Different aiding commands provide the same data in different reference frames (e.g. ECEF vs NED velocity.) Only one frame should be used at a time.
Tip: For best practices, installation, and recommendations on specific aiding sensors that have been field tested with the 3DM-CV7-INS, refer to the External Aiding Sensors page.
Aiding Frame Configuration
The Aiding Frame Configuration (0x13,0x01) command enables the user to mount an aiding sensor at a specific location on the vehicle and to specify the parameters of that frame. This includes an offset vector and a rotation with-respect-to the vehicle frame. See the Aiding Frames page for more information.
-
Enables user to configure relative translation and rotation for external aiding sensors
-
These frames account for the effect of vehicle dynamics on external aiding measurements
Aiding Command Echo Control
The Aiding Command Echo Control (0x13,0x1F) enables the user to control whether aiding commands are echoed back out of the 3DM-CV7-INS. This is useful for observing aiding measurements and their effects on the 3DM-CV7-INS filter output.
This is required for post processing support in our desktop simulator and is useful for troubleshooting.
ECEF Position
Use the ECEF Position (0x13,0x21) aiding command to provide a position measurement with-respect-to the Earth-Centered, Earth-Fixed (ECEF) frame. See Coordinate Frames for definitions.
LLH Position
Use the LLH Position (0x13,0x22) aiding command to provide a position measurement with-respect-to the WGS84 ellipsoid using Geodetic coordinates (latitude, longitude, height.) Note: Uncertainty must be in North/East/Down (NED) components.
This command can be used to input an absolute height measurement by setting the uncertainties or valid flags to 0 for Latitude and Longitude. As a reminder, this height is referenced to the WGS84 ellipsoid, NOT height above ground.
ECEF Velocity
Use the ECEF Velocity (0x13,0x28) aiding command to provide a velocity measurement with-respect-to the ECEF frame. This aiding measurement should not be used to supply a velocity from a body-fixed sensor, e.g. radar-derived velocity. For this type of sensor, use the Body Frame Velocity (0x13,0x2A) aiding command instead.
NED Velocity
Use the NED Velocity (0x13,0x29) aiding command to provide a velocity measurement in the North/East/Down (NED) local-level frame. This aiding measurement should not be used to supply a velocity from a body-fixed sensor, e.g. radar-derived velocity. For this type of sensor, use the Body Frame Velocity (0x13,0x2A) aiding command instead.
Body Frame Velocity
Use the Body Frame Velocity (0x13,0x2A) aiding command to provide a velocity measurement in a frame that is fixed relative to the vehicle. This enables the 3DM-CV7-INS to constrain its drift during periods of GNSS outage. The velocity must be provided as a pre-processed, 3-element vector. The 3DM-CV7-INS allows for up to 4 velocity sensor inputs of this type.
Examples of aiding sensors used to populate this aiding command are pre-processed outputs from radar, LiDAR, wheel speed measurement, wind-corrected air speed, etc.
Note: If an axis is marked as valid, but uncertainty is set as 0 or negative, an invalid parameter response will be issued
Ex: Body Velocity with height unavailable
| Description | Ex: Velocity in the body frame, height unavailable | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Notes | ||||||||||||||||
| Parameter Name | Data Type | Description | Value | Hex | ||||||||||||
| Field Length | u8 | 5 | ||||||||||||||
| Descriptor | u8 | 0x2A | ||||||||||||||
| Time | Time | Timestamp of the measurement. | 158000 | |||||||||||||
| Frame Id | u8 | Frame ID for this measurement (must be > 0) | 2 | |||||||||||||
| Velocity | vector3f | [m/s] | 3.745 | |||||||||||||
| Uncertainty | vector3f | [m/s] 1-sigma uncertainty | 0.120 | |||||||||||||
| Valid Flags | u16 bitfield |
|
1;1;0; | |||||||||||||
| Ack/Nack Reply | See standard MIP ack/nack reply format. | |||||||||||||||
True Heading
External heading aiding helps to maintain accurate vehicle heading estimates, especially during quasi-stationary periods with minimal linear acceleration. Use the True Heading (0x13,0x3A) aiding command to provide a heading measurements with-respect-to true north. This is commonly used to supply dual antenna / GNSS compass heading measurements.
External Magnetometer
Use the External Magnetic Field (0x13,0x32) aiding command to provide a magnetic field measurement from an external magnetometer. Note: this measurement is assumed to come from a calibrated source. A properly calibrated and thoughtfully placed magnetometer can be a good heading measurement for applications that experience GNSS denied environments. In the case where the 3DM-CV7-INS cannot be mounted away from magnetic interference, this command provides a method for inputting magnetic field measurements from a better situated magnetometer.
Ex: External Magnetometer with all fields populated:
| Description | Ex: External Magnetometer aiding measurement | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Notes | |||||||||||||||||||
| Parameter Name | Data Type | Description | Value | Hex | |||||||||||||||
| Field Length | u8 | 5 | |||||||||||||||||
| Descriptor | u8 | 0x32 | |||||||||||||||||
| Time | Time | Timestamp of the measurement. | 158000 | ||||||||||||||||
| Frame Id | u8 | Frame ID for this measurement (must be > 0 ) | 3 | ||||||||||||||||
| Magnetic Field | vector3f | [Gauss] |
|
||||||||||||||||
| Uncertainty | vector3f | [Gauss] 1-sigma uncertainty. | 0.031 | ||||||||||||||||
| Valid Flags | u16 bitfield |
|
|
||||||||||||||||
| Ack/Nack Reply | See standard MIP ack/nack reply format. | ||||||||||||||||||
External Pressure
Use the External Pressure (0x13,0x33) aiding command to provide a static pressure measurement. In the case where the 3DM-CV7-INS cannot be mounted where static pressure can be reliably measured, this command provides a method for inputting static pressure measurements from a better situated pressure sensor. Static pressure is used to constrain altitude drift during GNSS outages.