Filter Aiding Measurements
IMPORTANT: Features requiring a magnetometer are only available on device models with magnetometers. See Product Description to verify that your device has a magnetometer.
The 3DM-CV7 supports a variety of aiding measurements to improve the solution of the Estimation Filter. Aiding measurements are used to remove initialization and integration errors and maintain solution accuracy. Each aiding measurement (except external heading aiding) can be sourced internally from on-board sensors. Aiding measurements are enabled and disabled by the Aiding Measurement Enable (0x0D,0x50) command.
The availability and effectiveness of each aiding measurement will depend on the application and device configuration. To enable an aiding measurement, the Aiding Measurement Enable (0x0D,0x50) command must be sent once per aiding source. The table below captures the values that must be entered in the Aiding Source field to enable an aiding source.
| Aiding Source | Value Entered in Aiding Source Field |
|---|---|
| Magnetometer aiding | 4 |
| External heading aiding | 5 |
| External magnetometer aiding | 7 |
A description of each aiding measurement is given below, along with any additional configuration commands required to use the aiding measurement.
Magnetometer Aiding
A 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 be sourced internally
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 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] |
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| Uncertainty | vector3f | [Gauss] 1-sigma uncertainty. | 0.031 | ||||||||||||||||
| Valid Flags | u16 bitfield |
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| Ack/Nack Reply | See standard MIP ack/nack reply format. | ||||||||||||||||||
External Heading Aiding
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. The legacy External Heading Update (0x0D,0x17) and External Heading Update With Time (0x0D,0x1F) are still supported but no longer recommended.