LV_Forestry
 Second Officer
Flight distance : 4726654 ft
Latvia
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What follows is a bit long, it is intended for people who intend to do precision mapping with drones equipped with RTK receiver. If this is not your case, sorry, but no solution will meet your needs here.
I am in no way affiliated with the companies producing and selling the hardware and software mentioned below. Only one customer satisfied with the good price/quality ratio.
The DRTK2 works, it is not at all questioned here. What is problematic, in my opinion is:
-Its lack of clarity in its operation. The documentation is very brief. When I read the manual available on the product page of the DJI website I have the impression that the message is: "do what you can, good luck".
https://dl.djicdn.com/downloads/ ... uide_v2.4_multi.pdf
-During firmware updates there have been several times in the past floating moments where the receiver was unusable.
-To go from one range of drone to another, you have to do manipulations that I find cumbersome.
-The price is a bit high knowing that you can't use it to capture GCPs unless you have the P4RTK RC with integrated screen.
To overcome these problems I used until then a Trimble receiver, which allowed to rule out the problems of firmware, clarity of use... The fact remains that price level is well beyond the DRTK2, which is in itself a problem. More recently I had the unpleasant surprise to learn that the license of the software sold with the Trimble receiver had expired, impossible to reconfigure the receiver without spending a thousand dollars to renew the license.
So I looked into the problem, namely finding a cheaper, unlicensed receiver. I work regularly with the ZEDF9 range of receivers from U-Blox, which are very easy to integrate into various and varied systems. Forestry machine in my case. In addition, their accuracy is excellent when used with the correct antenna.
I'll make it short, while browsing the internet I came across the site of the manufacturer of the prototype boards that I use regularly and which offers this product:
https://www.sparkfun.com/products/18443
Knowing the reliability of the receiver, I decided to order it in its complete kit version, box + antenna:
https://www.sparkfun.com/products/17370
It is a simple product, its purpose is to provide precision coordinates in rover mode paired with a base station, and RINEX observations in base mode. The software is open-source:
https://github.com/sparkfun/SparkFun_RTK_Surveyor
To complete it I use a Bosch PRO BT160 tripod. It is originally designed for an optical level of the same brand but exists sold alone.
https://www.boschtools.com/us/en ... pods-bt160-34307-p/
You will find in the attached ZIP file the 3D models of the parts to adapt the antenna mentioned above. To be 3D printed or CNC milled. Everything is in metrics. If you need different dimensions feel free to ask. The receiver bracket is printed flat. Then heat the plastic along the grooves with a heat gun and bend the parts at 90 degrees. Use gloves and away from flammable materials!
Following a few requests, I will now describe how it works with the DJI L1 LiDAR for PPK. Why PPK? Because it is a fast and precise method. Better than RTK.
During the first use of the box, insert a blank SD card, then turn on the box in rover or base it does not matter.
A file named "SFE_Surveyor_Settings_0" will be saved on the SD card. It will allow you to configure the receiver. You can also use WI-FI or Bluetooth to configure it. I let you consult the official site which is regularly updated and well detailed.
SparkFun RTK Surveyor Hookup Guide - SparkFun Learn
After performing the initial configuration, open the file and check that the message "UBX_RXM_RAWX.msgRate" is equal to 1. Why 1? For one Hertz, one observation is recorded per second. That's more than enough for what we're going to do.
A/ Antenna instalation1st method/ you have access to an NTRIP network but a little too far to ensure the necessary precision in direct connection with the LiDAR.
A1/ Assemble the antenna on the tripod without using the pole. It is much more convenient to use. Try to put the antenna horizontally but no precision is required.
A2/ Open the SWMaps app on your smartphone. Then connect your receiver via Bluetooth. The height of the instrument must be zero!
A3/ Connect to your NTRIP caster by entering the credentials. This can be configured directly in the receiver if you let it have access to your smartphone's WiFi hotspot. It is faster.
A4/ Wait for the receiver to go into "FIX" status then press the pencil at the bottom right.
A5/ Tap "Record using GPS"
A6/ Check the "averaging" option then let the receiver establish an average of his observations. Be sure to be in "FIX" before doing this. You now have time to prepare the drone and warm up the LiDAR.
A7/ When the coordinates Lat Long and Alt ellipsoidal are stable, write them down on a paper or a TXT document on a laptop. Coordinates are WGS 84 decimal, UTM are not needed.
Note : You can perform this manipulation without the SD card being inserted in the receiver. Therefore you can write the coordinates directly on the Sd card TXT file (step C1). But keep these coordinates saved somewhere safe because they will be reused later in Terra.
A8/ Switch OFF the receiver and go to step C1.
B/ Antenna instalation 2nd Method/ There is no base station, no NTRIP, no GSM network, but there are geodetic markers.
B1/ Go to the website of the national geographic agency of your country then look for the closest landmark to your place to be mapped.
B2/ Go to the indicated place, take a shovel and look for the mark. The type of shovel does not matter but be careful not to damage the marker while digging. Some are extremely old and fragile. My technique is to probe with a concrete reinforcement metal piece before digging unnecessarily over several m2.
B3/ Install the antenna with the pole and the tripod on the landmark. The pole I use is the one that came with my Trimble receiver. Nevertheless it can be purchased very easily. No need for a carbon pole. On this pole there is a spirit level. It is extremely important to put the antenna perfectly in line with the marker.
Note : Do not screw too hard so as not to crush the plastic to keep the pole sliding smoothly.
C/Flight Preparation
C1 and C2 are necessary only if you want to broadcast RTCM. For an OBS file only, it is not necessary because these coordinates will have to be entered later in the post process.
C1/Open the TXT file present on the SD card and fill in the Latitude and Longitude coordinates of your previously installed base station. The one given by SWMaps for the first method, Those given by your geographical agency for the second.Take this opportunity to double check that "UBX_RXM_RAWX.msgRate" is equal to 1.
Remember : Coordinates must be WGS 84 decimal.
C1a/ Case of the first method : Enter the ellipsoidal elevation as displayed on the SW Maps app when acquiring the coordinates.
C1b/ Case of the first method : Enter the ellipsoidal elevation of the landmark provided by the geographic agency by adding the height of the pole, plus the distance between the base of the antenna and the center of the phase. It is mentioned on the documentation of the antenna and very often on a label glued directly above.
C2/ Be sure FixedBase=1 and FixedBaseCoordinateType=1. Save the TXT file then put the SD card back into the receiver.
Note: step C1 can be done entirely via Bluetooth or Wifi. Refer to the Sparkfun manual. Personally I prefer to do it manually.
SparkFun RTK Surveyor Hookup Guide - SparkFun Learn
C3/ Put the receiver in "base" mode before turning it on.
C4/ Turn on the receiver, wait a good minute to be sure that recording has started (red LED on), you are ready! To wait for this minute it is at this moment that I do the pre-flight visit of the drone. Check that everything is tight, clean lenses, clear environment...
D/Flight
D1/ On the RC, you can simply deactivate the RTK, then start your flight. With the LiDAR L1 the preview of the point cloud on the RC will be catastrophic without RTK but it is absolutely not serious issue. Unless you want to show a customer in real time how pretty it is. You can leave the receiver recording all day (If you operate within a 10km radius), if the battery is not enough, you can add a power bank through one of the two USB-C sockets. My built-in battery lasts about 4 hours.
E/ After the last flight
E1/ Turn off the receiver, save the SD card carefully. See you at the office!
F/ Work in the office
F1/ Start by copying and pasting on the desktop the .UBX file that is on the receiver's SD card.
Note: From this point you have several options. We'll stay within the L1 LiDAR framework, but if anyone wants to know how to get a RINEX file from it for example, just ask I'll gladly update.
F2/ Paste this .UBX file in every folders associated with flights performed with the L1 LiDAR.
F3/ Delete the .RTB file if it exists. If the RTK is disabled during the whole drone flight, this file must not exist. So don't worry if it is not there.
F4/ Rename the .UBX file by copy/pasting the name of the .RTK file which is different in each folder.
The Folder must look like that :
Note: For steps F2 F3 F4 it is also valid if you use an .OBS file from a third party RINEX data provider.
F5/ Open Terra, create a new point cloud reconstruction mission.
F6/ Add one or more folders, depending on the scope and the connections between different flights.
F6/ Enter the coordinates of the base station that you measured and provided to the receiver when it was installed, for Each Folder ! Latitude Longitude and Ellipsoidal altitude WGS84 decimal format.
F7/ Select the desired parameters for the reconstruction, start the process and a few minutes later, you will have everytime a magnificent geo-referenced point cloud with an accuracy of about 5cm counting the error of the PPK which will be of the order of a centimeter + that of the LiDAR and its IMU.
Say goodbye to RTK/IMU problem error messages that destroy whole days of work by surprise.
Once again, this receiver is not only dedicated to L1 LiDAR. It is compatible with absolutely all systems requiring files in RINEX .OBS format or U-blox in RAWX format. That is to say all DJI and other brand drones equipped with RTK receiver as mentioned at the beginning are compatible.
It can also be used as an NTRIP caster via SNIP/RTK2GO.
RTK2GO – Hassle Free RTK NTRIP Streaming
Simple NTRIP Caster – SNIP (use-snip.com)
From this .UBX file mentioned above it is possible to obtain a huge amount of information, and file format. It is possible to process it with RTKLib and Emlid Studio, among other things, to georeference drone pictures with precision.
The receiver can also be used to capture GCPs using it with SWMaps and the pole.
Hope you enjoy !
Sparkfun RTK Bosch BT160.rar
(239.2 KB, Down times: 24)
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