you can define which GPS should be used for GPS 1 (e.g. define the GPS Type and then serial port, or set the CAN preferences).
Imho it does not make sense to mix a Here 3 and a F9P module on the same drone. Stick to same GPS models (or at least same hardware, like 2x M8P, 2x F9P,…).
I have a Holybro M10 GPS (GPS1) and a Sparkfun ZED-F9P RTK GPS (GPS2) using a Survey Grade Antenna on my Rover.
When running the Rover navigation control module indoors, both the Holybro M10 GPS and the Sparkfun ZED-F9P RTK GPS will both initially show a “3D Fix” status which eventually changes to “3D dgps” as more satellites are acquired. Neither the “3D Fix” or the “3D dgps” GPS status have anything to do with RTK GPS (Base Station/NTRIP server) though a “3D dgps” status is superior to a “3D Fix” status.
If I run my RTK GPS Base Station outdoors, once the Base Station has completed its Survey-in and begins sending RTCM correction messages to the Sparkfun ZED-F9P RTK GPS, the ZED-F9P RTK GPS (GPS2) status will then display “3D rtk Float” followed by “3D rtk Fixed” while the Holybro M10 GPS status stays at “3D dgps”.
I will have to disagree with your statement that DGPS can improve the horizontal accuracy by 1000-fold which bring the horizontal accuracy down to around 1 -3 cm which is much closer to the accuracy achieved by only using RTK GPS.
In reality DGPS GPS will realistically achieve a horizontal accuracy of around 1 -3 meters.
Thanks for sharing.I understand that the can preferences can set the priority for GPS. But in the case where I’m using 2 GPS, one with Serial and one with CAN, I don’t think it will work in my case. I did however just found this parameter GPS_PRIMARY. I’ll need to check again if this will work when I have access to the drone again tomorrow.
@TCIII Hi Thomas, thank you very much for sharing. I wasn’t having much success trying to find the difference between 3D DGPS and 3D Fix in the context of ardupilot/mission planner, but the information you’ve shared has greatly cleared up my confusion.
May I check how is your dual GPS set up? Are they both on serial interface and on “blend” or do you have any settings to determine which is the primary GPS.
@ninervictor15,
Since the ZED-F9P RTK GPS is far superior to the Holybro M10 GPS I have the GPS_AUTO_SWITCH set to 1 “Use Best” as “Blend” can cause wild swings in the GPS localization if the ZED-F9P RTK GPS temporarily loses its “rtk Fixed” status for any reason and the navigation control module tries to use the M10 GPS module “3D dgps” for localization.
The Holybro M10 GPS is on the GPS1 serial input while the ZED-F9P RTK GPS module is on the GPS2 serial input of a Holybro Pixhawk 6x mini FCU.
I am attaching a photo of my completed navigation control module showing the relationship of the ZED-F9P RTK GPS module Survey Grade antenna and the Holybro M10 GPS module mounted on a module support. Both GPS antennas are very close to the turning axis of the Rover when mounted on the Rover chassis.
Thanks for all the feedback and sharing of setup everyone.
I’ve taken a look at the logs and played around with the settings. It appears that most most of the time the update rate is at 5Hz for both GPS with only very occasional dips into the lower update rate speeds. I’m thinking if the number of sat counts at the bottom left of the map only shows GPS1 (Here3) by default, even if GPS2 (F9P) has higher sat counts and has been set as primary GPS using the “GPS_PRIMARY” parameter.
Or its possible that missionplanner is not registering these parameter changes - as I did notice that changing the constellation using “GPS_GNSS_MODE” from using all constellations to only just QZSS gave me the same sat count of 11. I would have expect the sat counts to have dropped considerably by using only QZSS.
Depending on chip model and flash vs ROM they might work at 8Hz or 10Hz, but I believe general consensus is that 5Hz offers the best tradeoff between reliability and speed.
