Hi - I recently purchased the RTK Facet and have began using it. I’m a civil engineer so I have general familiarity with some survey-related terms and concepts, but I’m certainly not a surveyor. I’m using the Facet in rover mode and just using it to map features (think trees, etc.) and to layout new features (think fences, etc.). I’ve noticed the following apparent issues with my workflow and am hoping to get input from others.
When I first turn on the Facet and connect it to my iPhone using SW Maps, it begins in RTK ‘Single’ and reports horizontal and vertical accuracies of about 11 inches and 2 feet, respectively. Also worth mentioning that the ‘dot’ indicating my location lines up nearly perfectly with the aerial image seen in the SW Maps app.
After a few moments, it switches to RTK ‘DGPS’ and, sometimes, begins to report improvement accuracy. The ‘dot’ indicating my location lines up nearly perfectly with the aerial image seen in the SW Maps app.
Based on a YouTube video developed by Sparkfun (https://www.youtube.com/watch?v=-0vlPDOZx7A), I’ve tried to incorporate NTRIP corrections using this website (http://rtk2go.com/) which is featured by the Sparkfun video. To do so, I select the ‘NTRIP Client’ from SW Maps and use the website just mentioned as the ‘NTRIP caster address’, 2101 as the ‘NTRIP port’, and ‘bldr_SparkFun1’ as the ‘Mount Point’, all as shown in the YouTube video. When I do this, it switches to RTK ‘Float’ and the reported horizontal and vertical accuracies increase to about 3 inches and 3 inches, respectively. However, the ‘dot’ quickly shifts 10’-15’ away from the previously displayed location to one which no longer agrees with the aerial. Can anyone tell me why this happens and if it’s appropriate?
The other thing which I notice is that even when I place the Facet on a stationary surface, the ‘elevation’ value never seems to stabilize (though it generally stays within a narrow tolerance of a few inches, it’s rapidly changing up and down); is this appropriate?
Aha, I wondered if that might be the case but it wasn’t mentioned in the video so I wasn’t sure. I’m in Maryland, and when I scroll through the mount points, don’t see anything obvious. How might I find a mount point close to me? And how far away is close enough to provide useful & accurate corrections?
Also, assuming there is a mount point useful to me, how will I know whether I can trust the results? It seems problematic to me that it reports such a high level of accuracy despite it being in the wrong location (in this case due to my error of course).
Your response suggests to me that these are typically provided on a state-wide network; as in, I should look for one for Maryland, as opposed to one for say Baltimore (city in Maryland) or ‘East Coast’ or something else?
Also, that being the case, I can either pay for a network, or just accept the level of accuracy provided without NTRIP corrections?
I believe 20’ish States have Free Networks.
But there are many other options for RTK for the 30 States that don’t have free access.
Plus you can always install your own Base Station.
Haha Ok, I’ll research and try to find something. If you have suggestions of where I might look please share, but I’ll assume I can find something with the Google.
Any thoughts on my other question, regarding how the elevation (and x & y coordinates, too) don’t stabilize even when the Facet is stationary… just the way it is given that its receiving constantly changing input from the satellites?
I can’t speak for SparkFun, but they offer a PointPerfect Subscription for the Torch for $8/month.
You might want to sweet-talk them into the same subscription for a Facet
[Edit, Facet is different Firmware…I shouldn’t have mentioned this and got your hopes up]
That is typical for any accurate GNSS that’s not receiving a proper Correction Source.
You need to have a RTK Fixed solution before you have any real insights to the position.
Excellent, thanks for the tip. Is buying another Facet for use as a base station a solution, or would I still need other data, etc.?
In the meantime, I’ll forego the NTRIP correction and live with the ‘DGPS’ connection, can I trust that the reported location is within the reported tolerances of the actual location?
Lastly, what key words should I search for when trying to education myself on this topic? If there’s a book or something which would help clarify these questions I’d like to have it, but I’m unsure what to look for.
If you can post-process the NOAA CORS network can be quite useful to find local resources, and pull RINEX data, both observations, and world-wide navigation data.
Local county or municipalities may also have their own GIS or DOT resources they might share in various forms.
Another facet (or any of our base-capable RTK devices) can be used as a permanent base is definitely a solution, as long as its correction data will be casting to a rover within 10km. Beyond 10km solutions degrade so we recommend to stay under that radius
“can I trust that the reported location is within the reported tolerances of the actual location?” yep, accounting for epochs and whatnot…but I suspect you just asking generally and that’s a yes. You can survey-in at your closest nearby monument to verify and run a post-processed verification (4th topic on the left side in the link below)
