I am out the in middle of nowhere, no Cell Service, no WiFi, no Internet (no Power for that matter). I have 70 acres to survey some open plains, some forest.
I am trying to determine the best accuracy I can get given my situation. It seems the best option would be 2 RTK Facets one as a base, one as a rover, with LoRa Serial Transmitters. Or would I be better off with a RTK Facet L-Band?
Once I enter the forest, will my LoRa stream de-grade? or vanish completely? Should I setup my base station at the edge of the forest, to provide minimum distance between the devices? That is, are the LoRa devices like microwave dishes where any interference blocks the signal? or like Wifi devices, where the signal will bounce around and I might be able to pick it up?
Looking towards the future, Once I get Wifi, and Fiber-Internet to the property, I could use a Mosaic X5, which has better accuracy, but when acting as a base station, can it use a LoRa Serial device to transmit to my RTK Facet rover? Or is Internet (NTRIP) my only option? Even if the corrections are now coming from my Mosaic X5, will my accuracy with the RTK Facet improve?
Thank for all your help. Just trying to make sure I buy the right thing.
In such a case, I do post-processing with RTKLib. I setup a base station with the antenna fixed to bedrock using a dowel (so I can be back later with the exact same position). I power it h24 with a solar panel and a powerbank. Then, I go to the terrain with another device. I turn it on in an open area. For important points (cave entrance in my case), I leave the antenna on a tripod for 5 mn. The drawback is that you don’t know if you will get RTK fix until you do the post-processing.
LoRa is not design for high rate of RTCM corrections… but if you are alone in your area, it may be usable. LoRa also need direct view but a couple of trees may not be an issue. Have a look at the following video:
If you don’t need centimeter accuracy, you may also go to Unicore um980 that should be able to go down to 10 cm in static conditions thanks to PPP with Galileo HAS.
I’m actually trying to stake out trails, roads and buildings. My understand is that I can load the CAD file into SW Maps and overlay it on the “world map”. But when I staking out the corner of a building, I need as much accuracy as I can get.
The Facet L-Band does not have an L5 antenna, the Torch does, but it’s not clear to me if the torch can receive L-Band corrections. I think it can only receive corrections via the connected cell phone. But I could be wrong.
That’s not what the documentation seems to say. While the Torch has an L5 antenna. and can process PPP corrections (via Wifi using a cell phone as a hotspot). This page says that L-Band PPP is not available on the Torch:
If the docs are wrong, and the Torch CAN process L-band corrections, then this seems like the best option.
Correct, the torch can use the same PointPerfect corrections over IP, but not L-Band.
My 2 cents:
For Construction stakeout of a Building, a Base-Rover combo would absolutely be the best choice.
The easiest all around would be the Facet L-Band.
Under Canopy, the Torch (or other Tri-Band) should pull ahead.
I am coming to the conclusion as well that Base + Rover is the best option.
But here’s something I don’t understand. When you have a Base+Rover combo, is the Rover getting general Positioning data from the Satellites, and correction data from the Base? or does it get Both Position and Correction data from the Base?
I keep hearing the statement that the base needs to be a fixed point because the rover calculates position relative to the base. If I come back tomorrow and the base isn’t in exactly the same spot, then my rover measurement will be off.
But this means under canopy, a torch isn’t useful in a Base+Rover setup, because it doesn’t use the L1/2/5 antenna to get data, it uses the base. and the LoRa transmission from the base will have interference from trees. Or am I misunderstanding what is meant by relative here?
An oversimplified explanation is:
The Rover still calculates it position based on the GNSS signals it’s receiving from the sky.
The Base station is doing the same thing, but it already “knows” its location (even if it’s a bogus position).
Once operating in Base Mode - Say the first second that the Base computes a position that’s 2 feet North from its “known” position, it sends that Vector to the Rover. The Rover knows that the sum of all the error sources (Clock Time, Atmospheric, etc) AT THE BASE LOCATION caused a 2’ error to the North at the BASE, the Rover corrects its calculated position by that same vector, until it gets a new correction vector from the base (generally every second). It gets much deeper than this explanation.
But this is why we say it’s Relative to the Base. Because any error in the Base Station’s “Known” position is included in the correction vector that’s sent to the Rover.
One way to think of the Base-Rover combo is that it can give you a little tighter Precision, but not necessarily Accuracy, unless you establish extremely accurate coordinates on the Base first.
Since you have 1 basic Project Site (70 acre property), a Permanent Base Station Location with well established coordinates on the point would be the best situation for accuracy. A Mag-Nail in concrete, or drive rebar in the ground and use a centering cap, etc.
Find a location with the best view of the Sky for your permanent mark for the Base.
Instead of using “Survey In”, you would log 24 hours of data (several times if you want) and use a Post Processing Service to establish coordinates on the permanent Base Mark.
Forest Portion of the Property:
Personally, I’d consider any position logged under tree canopy to be rough “mapping” grade quality.
For your 70 acres with no Cellular/WiFi, I’d vote for the Facet L-Band, and just pulling a tape across the proposed Building Corners to Square them. Your Surveying experience will likely be much smoother with L-Band PointPerfect corrections in this situation. If there was good Cellular Coverage, I’d probably vote for the Torch for Tri-Band if the Tree Canopy is a large factor across the 70 acres.