Comments: Setting up a Rover Base RTK System
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How would you set this up with a single base and multiple rovers?
I recommend setting up a base that is connected to the internet, then have multiple rovers all getting their RTCM data over cellular and transmitting it to the roving ZED-F9x via Bluetooth.
What would you do if you were in a situation where a cellular connection is not possible? (very poor reception, using phone/tablet as the handheld device that doesn't have network service). Is it possible to have the radio link work with mutliple receivers?
There are a variety of serial radio modem options available. Some modems are point to point and have a confirmation packet that the remote transmits back to the transmitter. Others are just blind broadcasters. Pick a radio that is just broadcast and you should be able to transmit from one to many.
Maybe add a wish list populated with the recommended HW please.
That would be awesome!
Thanks,Mark
Thanks for the awesome tutorial. I have the base station able to go into TIME mode, however, I am having issues getting the rover module to properly connect. When I look at my base station packet console it is much less full than yours. I'm not sure if this could be part of the issue?
Ex. My packet console looks something like this:
22:05:30 R -> 52 NMEA-GLGSV
22:05:30 R -> 72 NMEA-GAGSV
22:05:30 R -> 46 NMEA-GAGSV
22:05:30 R -> 67 NMEA-GAGSV
22:05:30 R -> 59 NMEA-GAGSV
22:05:30 R -> 72 NMEA-GBGSV
22:05:30 R -> 33 NMEA-GBGSV
22:05:30 R -> 59 NMEA-GBGSV
22:05:30 R -> 52 NMEA-GNGLL
22:05:30 R -> 48 UBX-NAV-SVIN
22:05:30 R -> 25 RTCM3-1005
22:05:30 R -> 158 RTCM3-1074
Ok, i had some wires crossed and the rover now picks up the RTK signal. The mode it goes into is 3D/DGNSS/FIXED and the RTK LED on the rover board is off.
Sorry for the horrible formatting in my previous post about adding a geoid file to swmaps, I copied directly from a wiki page and it didn't turn out the way I had expected. I meant to mention that if you download the datum files from NOAA, you don't have to convert the file to any other format. The previous post had another post embedded that described using an open source tool to convert a file to the correct .gtx format. You don't have to use any tools if you use the NOAA supplied .gtx file right out of the ZIP archive. The other thing to note is that once the geoid file is loaded into swmaps, the 'orthometric' height indicator will have a value, not just a '-' . Also, the geoid computation for orthometric correction did not happen for data points already stored in the Android app. This means that any exports of data from swmaps of locations taken prior to adding the geoid file will not be corrected in the data exports. Only new points added after installing the geoid file will include the orthometric height in the data export.
What follows are the additional steps needed to convert the ZED-F9P ellipsoidal height(elevation) to orthometric height seen on commercial GPS units as 'height' using a computed geoid for a specific section of the Earth's surface.
For more info, use your favorite search engine and search for 'ellipsoidal vs orthometric height' for a full explanation.
https://community.opendronemap.org/t/sw-maps-geoid-file-format/10383
Sw maps geoid file format General Help PyODM uplanddog 28 January 2022 18:27 1
Hi All,
Does anyone have experience with using SW MAPS and would know which file format to use for the geoid file? no where in their manual does it explain the geoid file process, nor the format accepted by the software. 1 Like Maurice.Sobiera 28 January 2022 19:25 2
Do you mean the App: SW Maps - GIS & Data Collector - Apps on Google Play ? 1 Like uplanddog 28 January 2022 19:36 3
yes. 1 Like Saijin_Naib 28 January 2022 19:50 4
Developer seems quite nice.
Have you tried to contact their support? http://softwel.com.np/contact uplanddog 28 January 2022 19:56 5
yes however they have not gotten back to me. I have tried a few different file formats and loaded the file into the geoid directory, but its not showing up, which tells me the file is of the wrong format. There is not an import option that I can see. Its really a slick app for taking lat/lon of GCP’s, but to export the data with orthometric altitude you have to use a geoid file, ortherwise ortho height just says 0.
for some strange reason their manual has no explanation or directions for using a geoid file for orthometric altitude but its in the app… 1 Like uplanddog 30 January 2022 13:33 6
dev got back to me. sw maps uses the *.gtx file format for the geoid. you can also download eye4software geoid converter to convert geoid files. I converted a .bin file to .gtx for my area and am able to now observe and export data to xls/ods spreadsheet. works like a charm.
Find elevation with lat,lon for a control test in comparison to swmaps performance (remember to set your rover's antenna elevation too): https://www.advancedconverter.com/map-tools/find-altitude-by-coordinates
SW Maps Android release notes: https://aviyaantech.com/SwMaps/changelog-android.html
Download geoid file in WGS84 .gtx binary format at: https://vdatum.noaa.gov/download.php - download the zip file 'vdatum_GEOID09.zip' under the heading 'NAD83 and NAVD88', GEOID09 unwind the zip file and navigate to vdatum-2009/core/geoid09 in the archive where you will find the .gtx files that swmaps needs in it's 'geoid' app directory the vdatum-2009/geoid09.inf file lists the .gtx files by lat,lon area covered when constructing the geoid file. (eg. Colorado is file: g2009u06.gtx) g2009u06.cols=1141 g2009u06.maxlat=42.0000000 g2009u06.maxlon=266.0000000 g2009u06.minlat=24.0000000 g2009u06.minlon=247.0000000 g2009u06.rows=1081 g2009u06.source=core\geoid09\g2009u06.gtx g2009u06.spacing_lat=0.0166667 g2009u06.spacing_lon=0.0166667
After building a base station and a rover, and using the rover with RTK from the base station, including the rover's antenna height above the earth, and this geoid file with swmaps, I had less than an inch of lat/lon error and less than six inches of vertical error (height [orthometric]) at my location when compared to the result from www.advancedconverter.com .
Hi Nate! As predicted, I came back for another set of gear, plus radios, so now I have full remote RTK capability! I would like to understand how to resolve a problem I have, though. My property is out of cell coverage, and I can't leave equipment there (like a reference station - no power). I'd like to go back every so often and have repeatable results - when I take down my temporary Base and re-establish it the next time, the survey-in is still not terribly accurate (nor precise), and I'd like to fix that issue. Is there a way to establish a known location (like create a little survey monument that won't get disturbed), locate it accurately (if I'm doing the PPP technique, can I save the *.ubx file to the SD card? Can't leave a laptop there, but I do have a battery pack that can plug in to the RTK Surveyor to keep it going for a day or two), then set up over it next time, and have it understand that it is at a fixed location and broadcast RTCM corrections using that known location as a reference? The last bit I can do from your other tutorial - it's really how to collect that data for 24hrs in a remote spot that is something I am having trouble envisioning... Any guidance? Thanks, Neil.
How much accuracy, horizontal and vertical, do you need? Horizontal is pretty easy, vertical is an extra step.
If you need relative accuracy, I would hammer something into the ground, locate a tripod with a string+nut above the spot and do a Survey-in. Record these coordinates. Now every time you return to the spot, enter the coordinates into a fixed base. Day after day, all your plots will be extremely, relatively, accurate to each other. Ie, your base might be a few feet off compared to the 'real world' but the distance from your base to the rover will be accurate to 14mm.
If you need absolute accuracy, configure a rover for logging PPP messages. Set your unit over your monument and start it up. Let it sit for 6 or more hours. Take your PPP log data and send it through CSRS to obtain the absolute location of your monument. Next time you return to your monument, set your unit for fixed base, enter your CSRS obtained coordinates and your rover will have absolute accuracy.
The problem with both of these setups is antenna height. If you want really accurate readings (with either setup) you'll need to make sure your antenna's height off the ground is the same every time. This is very tricky with tripods as the legs can adjust and sink into the ground. Using a tape measure or sting can help reduce this variable.
Thanks Nate! I appreciate the quick and insightful response! I think I have a way of ensuring vertical accuracy in an absolute scenario, at least to a couple of millimeters, which should be 'good enough' for my purposes (remembering that "perfection is the enemy of good").
I am having a lot of fun skill building and learning how to configure the ZED-F9P with the ESP32.
I would like like to use the ESP32 to receive the RTCM corrections from the ZED-F9P through the UART2 port and deliver them via Bluetooth to a NTRIP Client. I get the physical layers, devices and connections however my programming skills are not my strongest point and I am wondering if anyone point me in the right direction?
Our group wants to read the GPS message on the Linux system by using the USB connection. Should we change the Port target to be the 3-USB? Or are there any tutorials about these we can follow? Thanks!
Thanks for writing up this tutorial!