INS

Applicable receivers:  AX940i | BD940-INS | BX940 | BD992-INS | BX992

Use this page to set the INS receiver settings. Select Receiver Configuration / INS.

 

INS Enable – Enable/disable the INS feature in the INS receiver. Select this check box to enable. If disabled, the receiver operates in GNSS-only mode.

General

GAMS (dual-antenna receivers only) – Enable/disable the GAMS (GNSS Azimuth Measurement Subsystem) feature in the INS receiver. Select this check box to enable. This enables the system to align when it is first turned on and before movement has occurred. If disabled, the receiver operates in single-antenna INS mode.

Mag Enable – Enable/disable the MAG feature within the INS receiver. Select this check box to enable. The magnetometer is utilized to provide heading before GNSS derived heading is obtained. This allows a static receiver to output heading when powered up. The magnetometer must be calibrated before this will occur. To calibrate the magnetometer, slowly drive the vehicle around in a tight circle a minimum of three times. The table below provides suggested circle radii and vehicle velocity for this procedure.

NOTE – The magnetometer must be calibrated for each general location. For example, if the magnetometer was calibrated on the East Coast of the USA and brought to the West Coast, a re-calibration is required.

Circle radius

Maximum vehicle velocity

Minimum circles

10 meters

~7–14 miles/hr or ~10–21 km/hr

3

20 meters

~13–26 miles/hr or ~20–40 km/hr

3

Once the calibration has been completed, the calibration values are stored in the receiver and the procedure only needs to be repeated if the receiver is moved to a different location within the vehicle.

Static Bench Testing – For field use, ensure that you clear this check box. This feature is useful for bench testing only. Static Bench Testing mode allows the INS receiver to enter an aligned status without movement.

Heading – The Heading setting allows the heading output to be specified when in Static Bench Testing mode. Trimble recommends after disabling the Static Bench Testing mode, that you restart the receiver to ensure that filters are cleared before resuming normal operation.

Receiver Motion (Dynamic model) – The BD940-INS and BD992-INS receiver modules come equipped with a set of dynamic models to best model the application being used. This feature is found in the Receiver Configuration / Position menu. Selections include:

  • Automotive

  • Mapping vehicle

  • Off-road vehicle

  • Off-road vehicle (Moving Start)

  • Airborne – rotor

  • Airborne – fixed wing

  • Marine

NOTE – The Reference to Real Wheel Lever Arm setting is needed if the Mapping vehicle or Automotive options are selected.

NOTE – There are two versions of the Off-road vehicle dynamic model:

  • The model labeled Off-road vehicle (Moving Start) begins INS operation if the receiver is powered up and the vehicle is moving.

  • The original, unspecified Off-road vehicle model requires the vehicle to stop completely for about three seconds to perform static calibrations on IMU components. INS positioning does not begin until this is complete.

Graphic Prerequisites

The graphic prerequisites, which establish the model dimensions and reference location from the center of the vehicle, do not affect the INS position attitude computation; these simply aid in model visualization.

The vehicle frame is defined as the right-handed orthogonal coordinate system with its origin defined in the center of the model. This coordinate system and its origin are only used for setup and does not affect output.

The reference is the point for which the INS position solution is computed (i.e. center of blade, camera focal point, etc.).

The reference frame is defined as the right-hand orthogonal coordinate system with its origin at the user’s defined reference. The reference frame defines the coordinate system in which attitude will be output (often coplanar with the vehicle frame, or this may be coplanar with a camera system's optical axes).

Scale Factor – Enlarges the antenna, board, enclosure models, reference, and rear-wheel markers to make them more visible; this has no effect on the setup.

Model Dimensions – Sets the size of the vehicle body for visualization purposes.

Reference Location from Center of Vehicle – Sets the location of the reference with respect to the center of the vehicle. This is helpful for visualization purposes, but all of the following lever arms will be made with respect to the reference (or with respect to something that is already measured against the reference).

Mounting Angles

Vehicle to Reference Mounting Angles – Rotations about each vehicle frame axis (in the order Z, Y, X) to establish the orientation of the reference frame. This will generally be left coplanar with the vehicle frame. In some cases, it may be desirable to rotate this to be coplanar with a camera’s optical axis. It is worth noting that this is a setup coordinate system, it does not need to be rotated to align with other coordinate systems, for example, rotating the reference frame to align with the typical ROS (Robotic Operating System) frame will invert the roll output. Angular measures are made around these axes:

  • X [Roll] – The positive x-axis in the vehicle frame points forward on the vehicle.

  • Y [Pitch] – The positive y-axis in the vehicle frame points to the right (starboard) side of the vehicle.

  • Z [Yaw] – The positive z-axis in the vehicle frame points downward on the vehicle.

Reference to IMU Mounting Angles – Rotations about each reference frame axis (in the order Z, Y, X) to establish the IMU mounting orientation. Keep in mind that these axes may be in different directions than the vehicle axes based on how the Vehicle to Reference Mounting Angles are set. In extreme cases, down in the reference frame may be up in the vehicle frame.

  • X [Roll] – The positive x-axis in the reference frame points forward on the reference origin.

  • Y [Pitch] – The positive y-axis in the reference frame points to the right of the reference origin.

  • Z [Yaw] – The positive z-axis in the reference frame points downward from the reference origin.

Vehicle to Receiver Mounting Angles – AX940i. To simplify the AX940i smart antenna setup, both the Vehicle to Reference Mounting Angles and Vehicle to Receiver Mounting Angles are measured in the vehicle frame. Rotations about each reference frame axis (in the order Z, Y, X) to establish the IMU mounting orientation.

  • X [Roll] – The positive x-axis in the vehicle frame points forward on the vehicle.

  • Y [Pitch] – The positive y-axis in the vehicle frame points to the right (starboard) side of the vehicle.

  • Z [Yaw] – The positive z-axis in the vehicle frame points downward on the vehicle.

GNSS Lever Arm

Reference to Primary GNSS Lever Arm – A three-dimensional vector defining the displacement of the GNSS Antenna Phase Center (APC) from the origin of the reference frame. These measurements should be made with subcentimeter precision. This displacement is measured in the vehicle frame, not the reference frame. The displacement is measured as follows:

  • X – The distance from the reference origin along the x-axis of the vehicle frame to the GNSS APC. A positive value implies the primary GNSS APC is forward of the reference (in the vehicle frame).

  • Y – The distance from the reference origin along the y-axis of the vehicle frame to the GNSS APC. A positive value implies the primary GNSS APC is right of the reference (in the vehicle frame).

  • Z – The distance from the reference origin along the z-axis of vehicle frame to the GNSS APC. A positive value implies the primary GNSS APC is below the reference (in the vehicle frame).

  • 1-σ – The user's estimate of how accurately the measurements have been made.

Primary to Secondary GNSS Baseline Vector (dual-antenna systems only) – A three-dimensional vector defining the displacement of the secondary GNSS Antenna Phase Center (APC) from the primary GNSS APC. These measurements should be made with subcentimeter precision. This displacement is measured in the vehicle frame. The displacement is measured as follows:

  • X – The distance from the primary GNSS APC along the x-axis of the vehicle frame to the secondary GNSS APC. A positive value implies the secondary GNSS APC is forward of the primary GNSS APC (in the vehicle frame).

  • Y – The distance from the primary GNSS APC along the y-axis of the vehicle frame to the secondary GNSS APC. A positive value implies the secondary GNSS APC is right of the primary GNSS APC (in the vehicle frame).

  • Z – The distance from the primary GNSS APC along the z-axis of the vehicle body frame to the secondary GNSS APC. A positive value implies the secondary GNSS APC is below the primary GNSS APC (in the vehicle frame).

  • 1-σ – The user's estimate of how accurately the measurements have been made.

NOTE – The functions to copy the Current Estimate of the lever arms, set the Target Heading Accuracy, measure the INS Heading Accuracy, and Auto-copy the results are part of a complex procedure for lever arm estimation when typical measure up procedures cannot be applied. For further information, see INS configuration application note or contact Trimble Support.

IMU Lever Arm

Reference to IMU Lever Arm – A three-dimensional vector defining the displacement of the IMU (from the center of navigation) origin from the reference. These measurements should be made with subcentimeter precision. This displacement is measured in the reference frame. The displacement is measured as follows:

  • X – The distance from the reference along the x-axis of the reference frame to the IMU (center of navigation). A positive value implies the IMU is forward of the reference origin (in the reference frame).

  • Y – The distance from the reference along the y-axis of the reference frame to the IMU (center of navigation). A positive value implies the IMU is right of the reference origin (in the reference frame).

  • Z – The distance from the reference along the z-axis of the reference frame to the IMU (center of navigation). A positive value implies the IMU is below the reference origin (in the reference frame).

Rear Wheel Lever Arm

Reference to Rear Wheel Lever Arm – A three-dimensional vector defining the displacement of the center of the rear wheel axle from the reference frame origin. (The X-axis component is of primary interest for this constraint and should be measured with a precision of a few centimeters.) This displacement is measured in the vehicle frame. The displacement is measured as follows:

  • X – The distance from the reference frame origin along the x-axis of the vehicle frame to the rear wheel. A positive value implies the center of the rear wheel axle is forward of the reference frame origin (in the vehicle frame).

  • Y – The distance from the reference frame origin along the y-axis of the vehicle frame to the rear wheel. A positive value implies the center of the rear wheel axle is right of the reference frame origin (in the vehicle frame).

  • Z – The distance from the reference frame origin along the z-axis of the vehicle frame to the rear wheel. A positive value implies the center of the rear wheel axle is below the reference frame origin (in the vehicle frame).

  • X [Roll] – The positive x-axis in the reference frame points forward on the reference origin.

  • Y [Pitch] – The positive y-axis in the reference frame points to the right of the reference origin.

  • Z [Yaw] – The positive z-axis in the reference frame points downward from the reference origin.