Relative INS

NovAtel's Relative INS technology generates a position, velocity and full attitude vector between two SPAN systems. One is the Base receiver and the other is the Rover receiver. Once configured, the Base receiver begins transmitting corrections to the Rover receiver. Relative information is created and the system begins filling the RELINSPVA log and SYNCRELINSPVA log on the Rover receiver. The RELINSPVA log is then transmitted back to the Base receiver for output.

The data link required must be able to support [864bits+108bits x #obs tracked per second]. The RELINSPVA log is requested ONNEW (available from 1Hz-20Hz depending on the setup of the RELINSAUTOMATION command) while the SYNCRELINSPVA log can be requested ONTIME at up to 200Hz (at the rover only). Position and velocity solutions are differenced in the ECEF frame and then rotated into the local level. The Relative offset vector that is output is dependent on Base/Rover's precise RTK vector and their eccentric offset vectors (optional offset provided using the USER parameter in the SETINSTRANSLATION command), shown in Figure: Relative INS Example.

Relative INS Example

An important command that can be used with Relative INS to manually change the maximum amount of time to use RTK data is the RTKTIMEOUT command. This command is used to set the maximum age of RTK data to use when operating as a rover station. RTK data received that is older than the specified time is ignored. The default is 60 seconds, however when using Relative INS, it is suggested this be set to 5 seconds by sending the command RTKTIMEOUT 5.

Refer to the RTKTIMEOUT command for more information.

Configure Relative INS

To configure the receivers to begin computing the relative information:

  1. Setup a link between the receivers that will be used to transfer data (for example, radios).

  2. Enable the transfer of relative corrections between receivers using one of the methods below.

To configure Relative INS using the RELINSAUTOMATION command, the base and rover receivers must be communicating using a COM port. If the base and rover are communicating via an ICOM port, the RELINSCONFIG command must be used.

The base and rover receiver must be using the same datum.