I have been researching RTK for several weeks and decided to go with SparkFun products for my project. The guides and community have been a great source of information and education. I have experience in electronics, manufacturing, and software development, but I am completely new to RTK.
I have some land where we’ll be building soon, and I want to set up my own surveying tools so I can locate points. I seem to have started this journey just as new products are being released, which is exciting but also making research a bit harder.
My Goal:
I want to position objects in a CAD drawing of the property, extract their coordinates, and then stake them in the real world–ideally within a few inches. In the future, I would love to explore robot navigation, but my immediate need is accurate point placement.
Planned Hardware:
2x RTK Postcard
2x Portability Shield
2x GNSS Multi-Band Antenna (SPK6618H)
Both setups would be battery powered. One on a tripod to function as the base and another on a surveying pole for a rover. I assume the Postcard’s ESP32 will make it easy to connect to my phone via Bluetooth for the rover side, but I need to decide how to communicate with the base station.
Questions:
Base-Rover Communication:
What is the best way to maintain a stable link between the base and rover at distances up to 1/2 mile?
I like the specs of the “LoRaSerial Kit - 915MHz (Enclosed)”, but I’m not sure if it is compatible with the Postcard. Is LoRa a good choice, or would something else work better?
Portable vs. Fixed Base Accuracy:
Is a fixed base better only because it has a precisely known position, or are there other benefits?
I’ve seen a lot of examples of people placing a base directly above a known point and setting a manual position, but using the rover to hit a known point to calibrate the system would be a much easier workflow because I can set the base in a safe location near the work area and no tape measure or alignment would be necessary.
Would this hardware support that workflow, or would I need to find mapping software on my Android device that can handle the offset automatically?
I would really appreciate insights from anyone willing to help.
What is the best way to maintain a stable link between the base and rover at distances up to 1/2 mile?
WiFi is best, then cellular (you’d need two phones, one for the base, the rover is usually your own phone). If neither of these is viable at your site then yes, a packet radio is the next best option to go 1/2 mile.
Since you’re just getting started, I’d recommend not focusing on the radios for now. Get your Rover/Base working at home with cellular and WiFi, and then move to the internal ESP-NOW radios. They work great up to about 500ft.
I’ve seen a lot of examples of people placing a base directly above a known point and setting a manual position, but using the rover to hit a known point to calibrate the system would be a much easier workflow because I can set the base in a safe location near the work area and no tape measure or alignment would be necessary.
Personally, I would drive a stake or marker at the site. Then capture 24 hours of RTCM, run a CSRS based PPP on the data. That will tell you the exact location of the marker. If altitudes are important, read up on Antenna Reference Points and be sure to subtract your pole length and ARP from your results to get marker’s accurate altitude. Then, store the known coordinates in the base (see Fixed Base mode). Every time you setup on site, put the base over the marker and turn it on. All readings from your rovers should align between days of capturing points. If you want to get really accurate then you need to take multiple days of PPP and compare, throw out any that look off, and average those within bounds.
@Breakfast Another thing to consider is that UM980-based receivers, unlike LG290P-based ones, don’t seem to require much fiddling. If you are completely new to this technology, it might be wiser to go for a device that has mostly functional firmware.
A minimum rover configuration doesn’t require an MCU or a wireless interface (depending on your phone, of course - it has to support serial-to-USB connection over the cable for that to work).
Great advice. I like the idea of just getting the boards to try at home. I had no idea ESP-NOW existed. That sounds great. What does it use for an antenna?
Good idea with putting a marker on the site. In fact, I wonder if I can build a contraption that locks the equipment into place consistently so I don’t have to fiddle with alignment.
I’ll research antenna reference points and some of the other acronyms and learn as much as I can on that path.
Thank you so much for the ideas and concepts to further my research!
just so you know a total station would make a much better job of this and staying accurate. We rarely use GPS for construction staking. With love a land surveyor then you can just live in an assumed coordinate system, don’t have to worry about grid-ground scale factors, etc, etc.
Fixed base works on the principle that you have assigned or known coordinates let says 10000,10000 you can then correct your RTK rover on the fly. You can get the base point very precise as desired but it’s not really necessary because it’s all relative. A lot of surveying is about being relative to other measurements. Whether it’s horizontal or vertical. So do I care that the base point is exactly on state plane coorindates down to 0.01’, no. Do I want point 1000 to be relative to point 1050 by 0.03’, yes. Just some food for thought. Elevations have gotten quite good with GPS but anything that requires elevation we still break out a total station. You could also use GPS and run a dumpy level through them. That would help you increase vertical accuracy.
I had no idea ESP-NOW existed. That sounds great. What does it use for an antenna?
ESP-NOW uses the same internal 2.4GHz antenna used for Bluetooth and WiFi. It’s really handy for small amount of data sent between two points, where BT/WiFi is better for large amounts of data (music, HTTP, etc).
Thanks for the advice, everyone! I ended up ordering the Postcards and other accessories to give that a try. It came in a few days ago. I spent an evening soldering the headers, updating the firmware, and making sure they work, but haven’t had time to really experiment beyond that.
I’m very impressed by the Portability shields. They work great and add a ton of value for very little money.
The next step is to make enclosures for the electronics so I can mount them on poles. I’m thinking of using Lego to get something built quickly. Then I will pair the ESP-NOW radios and do some experimentation!
Hi! I finally had some time to try out the Postcards, but I’m having trouble.
I can’t seem to get a fix from the rover. I’m sure I am missing a vital step or maybe I’m just in a bad area. Here is what I have done after factory resetting both devices:
Base:
s - Configure System
B - Switch to Base mode
x - Exit
Both devices:
r - Configure Radios
1 - ESP-NOW Radio: Disabled
2 - Pair radios
x - Exit
x - Exit
The base device begins doing a survey. After a while I see a blinking upload symbol in the top status area of the screen. The rover shows a blinking download arrow with a radio symbol next to it.
I assume that means they are communicating and the rover is incorporating correction data. The rover changes from 3D Fix to RTK Float according to the terminal, but the rover accuracy can vary anywhere from 1 to 13 meters. I think what I’m looking for is RTK Fix.
Is that an indication that my GNSS signals are unstable or do I need to configure more settings? I am testing indoors where my computer is. Taking it outside didn’t seem to help much at all, but there are some trees and buildings nearby.
Side note: I switched the base to Fixed/Static Position as part of my testing. I noticed that when I set the coordinates to something close to the actual base position, the base continues showing RTK Float. But if I set the position to something 100 meters away, the rover downgrades to 3D Fix. What is causing that? Is there code in the firmware that rejects the location as valid if it’s a certain distance away from the calculated position according to GNSS calculations?
I know with Lora I had to configure and make sure the baud rate was correct.
My steps to get it to work were, put my postcard in base mode, after a bit of time it surveys in and begin transmission over Lora radio, then using my rtk facet with a Lora radio connected in rover mode I can watch the accuracy drop into fix mode.
Are you trying to use espnow? Or some other radios to transmit serial data.
I think you’re trying to do espnow, I was never able to get that to work with my 2 postcards when I tried. But I also want long range so I was going Lora anyways.
Yes. I was trying to use ESP-NOW as an easy way to experiment. My ultimate goal is going to require more range though. I’m trying to decide between LoRa and internet-based transmission. Internet is appealing because I could potentially get that working now with two phones. But I could be convinced to order the LoRa radio kit if I knew there were proven working configs using 2 Postcards.
If I want to use the Internet, is NTRIP the tried and true way to set things up? That was a rabbit trail I was trying to postpone until later when I have the infrastructure to set up a permanent base.
Can that be done via Bluetooth on both phones or would I need to turn on hotspot mode and use WiFi?
Give me about a week to test out Lora I have one antenna with the bigger gain I want to do some experimenting. The only thing I’ve noticed is high fixed ages then dropping back to dgps. Where on my states RTN network I never see this. Granted trying to use facet and postcard together vs postcard postcard like I want to try when I get it back.
Awesome. Thank you. Are you using the Sparkfun LoRaSerial kit or another brand/model? I saw a few posts where people were having issues with that for this use case, so I was a bit nervous to order it.
I am happy to report that my RTK Float issue did seem to be related to the quality of my test area. I took the equipment to an open field and was able to get a lot more satellites and achieved RTK Fix. I finally got to experience the full accuracy and it lived up to my expectations (as long as I stayed within the range limits of the ESP-NOW).
I will likely experiment with using phones if I have any spare time this week. That looks like a trickier path than radio, but I think it would be valuable to have both options available.
Yeah I’m using the Lora kit. I think in some investigation through the manuals mAybe I need to try low bandwidth config for base config because Lora probably cant pump the bandwidth that ntrip or espnow can. I have seen some drops in rtk fix so I’m thinking I am flooding it with regular rtcm transmission. I typically use my postcard with my states RTN with excellent accuracy but I want an alternative when cell service is non existent.
then you can just live in an assumed coordinate system, don’t have to worry about grid-ground scale factors, etc, etc.