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Compensating the installation position


The ADMA, the GNSS antenna and external speed sensor can’t be mounted at the very same spot. The devices are placed at different positions in or outside the vehicle.
Usually:
• GNSS antenna is mounted on the roof
• ADMA close to the center console or in the boot
• External velocity sensor on the side, front or rear of the vehicle.
The distance between the individual components is termed “lever arm”.

As a consequence, the position measured by the GNSS antenna does not correspond to the virtual measuring point (reference point: Point Of Interest). An uncompensated lever arm also causes roll, pitch and course changes which need to be registered as errors in the form of position discrepancies. With data output V3.x it is possible to define up to eight POI’s.

Furthermore, the speed measured at the installation position of the external velocity sensor is not equal to the speed at the virtual measuring point. While the vehicle is travelling through a corner or in a circle, the speed measured by a sensor which is mounted on the vehicle's outer side is higher than the speed measured in the middle of the vehicle or inside the vehicle.

Installation positions are compensated by specifying the position vectors ADMA relative to GNSS antenna and ADMA relative to external speed sensor. With these lever arms the GNSS sensor data and the sensor data of the external speed sensor are factored into the calculation of the position such ensuring the correct transformation of ADMA related data to the POI. The position vectors are entered and edited in the ADMA Webinterface Offsets dialog. For determination of the installation position a folding rule or reference tape is completely adequate.

Webinterface: 6️⃣ Parameters / Mounting Offsets

Single antenna mounting offsets#

The position vector for the GNSS antenna consists of all three components (X, Y, Z) and refers to the ADMA.

Dual antenna mounting offsets#

The easiest way to install the dual antennas is to place both antennas on the same longitudinal axis at the same height. The primary GNSS antenna should be installed behind the second antenna with a minimum distance of 50 cm to a maximum distance of 200 cm. Thus, no configuration of the offsets between the Secondary GNSS Antenna to the Primary GNSS Antenna in the ADMA Webinterface is necessary. Only the mounting offsets between Primary GNSS Antenna and ADMA must be defined.

In case of lateral or height offset between the antennas, the descending offsets must be configured in XYZ axis via ADMA Webinterface.

Warning: It is important that both antennas are of the same type. Using two different types of antenna may cause the solution to fail.

Determining the offset between the GNSS Antennas and ADMA#

Mounting offsets Primary GNSS Antenna to ADMA#

The Primary GNSS Antenna always refer to GNSS ANT1 interface of the ADMA. This offset must always be determined.

Mounting offsets Secondary GNSS Antenna to Primary GNSS Antenna#

The Secondary GNSS Antenna refers to the Primary GNSS Antenna, in case of lateral and/or height offset between Primary and Secondary GNSS Antenna the offsets must be determined.

Virtual measuring point (POI - point of interest)#

If the ADMA is not mounted directly at the required measuring location, then a lever arm exists between the virtual measurement point (Point Of Interest / POI) and Measuring Reference Point of the ADMA (MRP). This lever arm can be compensated by entering the offsets to the virtual measurement point.
• X (positive in travel direction)
• Y (positive leftward with respect to direction of travel)
• Z (positive upward)
With the current data format version up to eight POIs can be defined in parallel.

Note: This compensation is only valid, assuming that the car turns around a virtually fixed axis and the movement of this axis in the horizontal plane is insignificant relative to the vehicle. However, this compensation is incorrect, if the axis doesn’t fulfil the above mentioned condition. For example, this could happen in driving situations like spinning or drifting i.e. the axis moves obviously.

Applikationsingenieur | bei GeneSys seit 2014

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