Position

Applicable receivers:  All receivers

Use this page to set receiver position-related settings.

Select Receiver Configuration / Position.

 

PDOP Mask – Use the PDOP mask to enter the value for PDOP above which the calculation of new RTK positions is suspended until the PDOP falls below the mask value again. A DGPS position is output when the PDOP for the RTK position exceeds the PDOP Mask.

RTK Mode – Set the RTK Mode to Synchronous or Low Latency.

• Synchronous – The rover receiver must wait until the base station measurements are received before computing a baseline vector. Therefore, the latency of the synchronous position depends on the data link delay. A synchronous RTK solution yields the highest precision possible but is subject to latency. This mode is suitable for static and low-dynamic positioning. When in INS mode, the Synchronous RTK mode is not available (the system runs in Low Latency mode).

• Low Latency – Provides a slightly lower precision solution than Synchronous mode but with a constant low latency, typically less than 20 msec. This mode is ideal for high-dynamic positioning where latency is an issue.

RTCM 2 Type 31 Input GLONASS Datum – If receiving RTCM 2 corrections from a GLONASS source, you can select the datum (PZ90 or PZ90.02) that they are based on.

Autonomous/Differential Engine – By default, the Kalman filter is on and results in higher quality position solution for autonomous or DGPS solutions when compared with a Least Squares solution. The Kalman selection works substantially better than a Least Squares solution in a mobile vehicle when there are frequent satellite signal dropouts around bridges or high buildings, and gives improved performance around forested areas.

A Kalman solution uses the time history of the position and velocity it has created, whereas a Least Squares option does not use the time history. Trimble recommends using the Kalman filter for most operations. Select Least Squares for non linear movement such as on a suction cutter dredge.The Least Squares option is available for applications where this may be required.

Signal Tracking Bandwidth – Allows for a DSP (Digital Signal Processor) selection for Wide or Narrow band tracking. The default is Wide band.

• Wide – Used for high-dynamic applications to allow the signal tracking to compensate for a higher rate of change in the Doppler frequency caused by antenna movement.

• Narrow – Used in low-dynamic applications where only relatively small changes in Doppler frequency are expected from antenna movement. Narrow bandwidth signal tracking allows less noise to pass through the filter to improve low-dynamic positioning with better accuracy.

Receiver Motion (Dynamic Model) – As an aid to the Autonomous/Differential engine, you can select a dynamic model which best describes the dynamic environment for positioning.

The Marine model is only intended to be used on dual-antenna systems with GAMS enabled, allowing the vessel to align and maintain alignment when at rest or when moving slowly.

Dual-antenna systems with GAMS are recommended for slow moving operations, generally motion slower than 3 kph. Velocities slower than this may fail to align the heading solution or provide heading solutions with larger error estimates/uncertainties.

When operating in GNSS-only (non-INS) mode, the dynamic models fine tune signal tracking and positioning parameters, although the changes are minimal and there is minimal impact if the incorrect model is selected. The notable exceptions are for:

• Static: Where the antenna is expected to remain in the same position, thus the navigator and velocity models are significantly different than all other models.

• Airborne rotor or Airborne fixed wing: Where a tropospheric model is applied to correct for altitude.

• Marine: Where the vessel is never expected to be truly stationary due to currents and wave motion on water. Also, with this dynamic model the NMEA ROT message is smoothed over a 10 second period to remove heading noise.

For INS operation, there are a limited set of available dynamic models that more significantly affect performance. These are described in the following table:

Dynamic model	ProPoint INS
Mapping vehicle	Rear axle motion constraints (heading = track) Heading constraint when stationary Heading initialization from GNSS track (if GAMS is not available) Required static start for initial gyro calibration
Off-road vehicle	Heading constraint when stationary Heading initialization from GNSS track (if GAMS is not available) Required static start for initial gyro calibration
Marine	No static start requirement Heading initialization from GAMS
Automotive	Rear axle motion constraints (heading = track) Heading constraint when stationary Heading initialization from GNSS track (if GAMS is not available)
Off-road vehicle (Moving Start)	Heading constraint when stationary Heading initialization from GNSS track (if GAMS is not available)

The primary considerations for users are:

• Whether or not the machine can “crab walk” (often seen on off-road vehicles where the rear wheels may be sliding down a slope) or if the heading and track angles can be constrained (with the rear wheels following).

• Whether or not the model requires a static gyro calibration at start up (~3 seconds stationary before INS can start). The static gyro calibration can help to minimize gryo bias errors, although the effect is typically negligible. If the static gyro calibration is required, INS operation will not begin until the static gyro calibration is completed.

RTK Propagation Limit – Defines the maximum age of the corrections, in seconds, which the RTK propagation will extend to. Values are selectable between 10, 20, 40, 60, or 120 seconds. When this maximum age is exceeded, the position solution will switch from RTK to DGNSS, SBAS, or Autonomous.

 

DGNSS Age of corrections – Defines the maximum age of the corrections, in seconds, for each constellation. When this maximum age is exceeded, the corrections are not used in the position solution. The solution will switch from DGNSS to SBAS or Autonomous.

Position Output Source – Only available when the receiver is in Heading operation mode.

• Derived – By default, the receiver outputs the position derived from the Moving Base receiver position plus the Moving Base vector.

• Native – The Heading receiver outputs a position that is not derived from the incoming Moving Base CMR corrections, but the next most accurate position such as OmniSTAR or an SBAS or autonomous position.

 

For Trimble RTX-capable receivers, running firmware version 6.20 and later, the following menu items are available:

ITRF Realization (2020)

Epoch – The default is Current.

• Fixed means ITRF2020 (2005.0 Epoch). Fixed to an epoch means that a point surveyed at different times will use the same transformation and result in the same position irrespective of any movement in the tectonic plate during the time interval.

• If Current is selected, then the latitude, longitude, and height are determined on the ITRF2020 reference frame for the current date accounting for any movement in the tectonic plate. The same point surveyed at different times may use different epochs in the ITRF Realization (2020) and result in different positions depending on the movement of the tectonic plate.

Apply ITRF Transformation to – RTX selection is the default setting. If None is selected, the RTX position is computed on the ITRF2020.

ITRF Epoch – This field cannot be edited and shows you that when Fixed Epoch is selected, then the 2005.0 Epoch is used.

Tectonic Plate – When the Current Epoch default setting is used, the receiver uses its position and automatically determines which tectonic plate it is on. The Auto setting is default. If the drop-down menu is opened, the selected plate and the four closest plates to the receiver position are listed. The Fixed epoch allows you to select another adjacent tectonic plate.

Recalculate – Click this button to force the current position of the receiver to be used to recalculate the selection of the correct tectonic plate. This button can be used when the Tectonic Plate is set to Auto. Other than at receiver power on, the receiver firmware does not continuously update the Plate selection if Auto is selected.

Click OK to apply the changed settings to the receiver.