Facet L-Band V. RTK Express and accuracy questions

GPS/GNSS Development Boards
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I’d like to map out a path while driving in a vehicle in a rural area without cell reception, short segments may be near a high cliff and through some short tunnels. Would have the antenna mounted on the roof of the vehicle and could have an android device available.

I’d like to log a point every foot. Is there a way to set either device up to log at a distance moved without an android device. I believe SW maps can log a track at a time interval and based on a distance travelled. 1M in the settings I have. Does the onboard device logging also work or is a data collection app is the right tool? Any better alternative to SW maps?

Does and/or how much will the accuracy be reduced when moving?

Would generally be mainly below 15mph. But it could be up to 25mph.

Would going slower improve accuracy? If so, how much?

I assume the facet l band does not have an IMU, correct? Is there a way to add it with external hardware?

Would the IMU in the Express plus help substantially areas with poorer sat signal?

I would obviously like the position to be as correct as possible but in most cases I really just need the points to be accurate relative to one another- including short tunnels.

On the Lband facet how long will the ublox $500 ongoing service last?

I like the idea of the lband facet but I believe my use case points me to think the RTK express plus (with dead reckoning) is a better option. Or is there another better tool for the job?

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With all things in life, it depends! (Sorry)

Because of the cliff wall, RTK fix with any setup may be a problem, it’s hard to say. If the cliff walls are short, you’ll likely maintain RTK fix for 30 seconds when reception is low. So if you pass the obstruction quickly, you could be ok.

I believe Facet L-Band will do most of what you need. You’ll get RTK float and RTK fix in areas where reception is decent. The exception is that L-Band requires a view of the southern hemisphere so I worry that your cliff wall will cause a lot of problems. The tunnels will cause lots of problems. Perhaps you can extrapolate the points between the openings assuming the tunnels are straight.

Are you planning on setting up a base? With no cellular reception, the RTK Express will need to obtain its correction data from a 2nd unit (setup as base) over a radio link.

If it were me, I would likely setup two RTK Expresses, one as base, and link them via radio. I’m not sure the length of the road you’re trying to survey so radio range could be a problem. 1/2 mile is not a problem line of sight, but more than that it gets tricky.

Using the RTK Express Plus works well for tunnels but you will need to assist it by providing wheel ticks from your car.

I’d like to log a point every foot.

Unfortunately all the receiver settings are time based, ie, 4Hz or 4 fixes per second is the default. You’d need to post process your data to get to a point per foot.

Does and/or how much will the accuracy be reduced when moving?

Nearly zero. The ZED-F9P is primarily designed for cars.

Would generally be mainly below 15mph. But it could be up to 25mph.

I think the max speed is something like a jet fighter, so you should be good :slight_smile:

Would going slower improve accuracy? If so, how much?

Generally no. But if we want to get technical: surveyors will ‘sit’ on a point for a few minutes to average stuff. As long as you don’t care about a +/-10mm, I wouldn’t bother.

I assume the facet l band does not have an IMU, correct? Is there a way to add it with external hardware?

No.

Would the IMU in the Express plus help substantially areas with poorer sat signal?

The IMU would assist in the tunnels but it requires a wheel tick signal from the car to work.

On the Lband facet how long will the ublox $500 ongoing service last?

12 months

I believe my use case points me to think the RTK express plus (with dead reckoning) is a better option

Note that the RTK Express Plus cannot enter base mode so you’d need an RTK Express as base, and an RTK Express Plus on your vehicle.