> For the complete documentation index, see [llms.txt](https://docs.ceruleansonar.com/c/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ceruleansonar.com/c/surveyor-240-16/faq.md). # FAQ #### Q: Does Surveyor integrate its own GNSS system? A: Surveyor does not include a GNSS device, but SonarView integrates and logs GNSS data from external devices. #### Q: What GNSS external devices are supported? A: With BlueOS based vehicles, SonarView connects via MAVLINK2REST to collect and integrate vehicle position and heading information. A: GNSS devices with NMEA output are also supported. Please refer to [these ](/c/surveyor-240-16/platform-specific-setup/nmea-position-heading-source.md)instructions for more details. #### Q: Does Surveyor have an IMU? A: Surveyor has a built-in IMU for roll and pitch compensation. Heading information is supplied by the vehicle (BlueOS/MAVLINK2REST or NMEA). Surveyor also has a compass which we might support in the future, but we think best to use the vehicle's heading information. #### Q: Where is the phase center (reference point) A: The acoustic phase center is determined by the receive elements inside the array module on the front of the unit. Below is a diagram showing the location of the acoustic center of the Surveyor 240.