I would like to start that discussion about the Open Source software RTK-LIB that allows anyone to post-process GNSS observations (RINEX) for free and also to perform RTK (RTCM).

It seems UAV hobbyists and robots makers are more familiar than surveyors with the RTK-LIB. That library has been developed by Mr TAKAZU from Japan. 

RTKLIB is an open source program package for standard and precise positioning with GNSS (global navigation satellite system). RTKLIB consists of a portable program library and several APs (application programs) utilizing the library.

I would very much appreciate your feedbacks on that topic and on what GNSS post-processing software you are working with ? It seems post-processing a bit of fashion nowadays but RTK-LIB can also carry on your observations in RTK mode and even using PPP.

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Sounds like an interesting discussion to come. That's why I'm commenting. We use a dial in to get our initial fix then use a base with transformation to ostn15 but that's just the UK
The big boys – Trimble, Leica, Topcon – have had these capabilities for a couple decades. Pretty much run-of-the-mill GNSS surveying methodology and technique.

Hi Kevin, absolutely right and portion of RTK codes have been taken from DELFT source code for the Lambda method. I still remember the first "commercial" post-processing software from Trimble (TRIM640 ?) also inspired by OHIA state University. Leica also at that time used the Bernese source code. Now what I find personally so exciting is that RTK-LIB is open source and so flexible by providing much information than any other else. Last not least, we had a problem with LGO licensing in Kuwait and we faced several days without any possibilities to work with. Then we switched to RTK-LIB and keep going. When LGO was back on track ... we compared results and found that not only all the results were closed to sub-mm but for one point there was a 20 cm gap. How was right or wrong ? We delegated a surveying team to check with a total station and found RTK-LIB was right. So even if you are at ease with existing post-processing softwares ... it's worth to double check your results with an independent one ... and for free !

I will add my viewpoint.  This is a broad subject and I am coming from the point of view of a commercial drone pilot.  Last year I began the quest to begin drone mapping and 3D modeling.  I knew from the beginning I had to understand and learn about GNSS, Surveying, and Post Processing in order to develope any skills and move forward.

I found out VERY quickly why Civil engineering is a degree and not a hobby!  I have done and learned many things in my 25 year professional career but there has been nothing harder to comprehend than Post Processing.

I have 2 Emlid Reach RS units and 1 Emlid Reach unit to put on my drone.  Before the Emlid Reach units it was cost prohibitive for anyone like me to aquire equipment and learn how to do this stuff.

So with that said, I dove in head first and tried to learn all that I could.

From a drone/uav standpoint, if you can take photos with RTK accuracy then there is no need to post process.  But when using drones like the DJI Phantom 4 Pro, it takes modifying the drone to be able to do RTK and even requires post processing the images to update the EXIF data with the RTK captured data.  I purchased the Emlid Reach unit to do this but have yet to implement it.  One barrier to RTK is the cost of having the correct access to NTRIP servers.  I have access to one server in North MS but that is it.  It is very costly.

I tried to learn RTKlib and after many days (actually a couple of months) I finally gave up on learning it.  I then found software from a company called Efigis (out of Canada).  And spent alot more time trying and testing different things.  I eventually settled on using their Post Processing software called EZ Surv and I survey Ground Control Points using their software called EZ Tag.  I can now go collect data, come back and post process the data with CM accuracy.  But it was a very long and hard rode to learn this stuff.  

With the growth of uav mapping, there are been many more guys trying to figure this stuff out.  For me it will stay with capturing points and post processing them.  It is fail proof and it works.  I know that RTK is great and when you have access to the NTRIP corrections, it is awesome and when I am close enough to the one caster that I have access to, I will probably do that and then just count on post processing when I am beyond the max distance.

As for RTKlib, for the guys who know this stuff, I know it is a great program and it works.  But until I have more time to try and learn it, I will have to rely more on an automated approach :)

I am just admiring you for keeping going through all the obstacles to finally succeed ! Yes you are right EZ software is very good and powerful and will keep you out the burden of fine tuning parameters etc, ... Just when you have time, step back on RTK-LIB and I am sure you will appreciate. Post-processing GNSS for UAV operations make sense for me because you will have anyway to download your images after the flight. So no need to geolocate your images with RTK. Now the survey of GCP's can be reduced and even not considered when you fly RTK. If you flying in small, medium area, a GNSS local base station will be nicely the job. But honestly RTK will become "mandatory" the day we will be able to also process the images in real time. Thanks for your reply !

Tim, I have also got a set of Reach receivers to use in a base/rover setup for GCP's for my little drone company. PSA - I am a surveyor for more than 30 years and understand the pain of getting post processing right. The problem I have is the free Australian processing required L1/L2 data and the Reach is only L1 - not a problem to use and get good RTK in the field but I can't post process the Reach Data here. How expensive is the EZ Surv program and what do you use with EZ Tag for GCP's - is it an app or what runs it? I'm keen to try what you've done with EZ Surv. Cheers.

Paul, 

The EZsurv is GREAT.  It now takes me about 2 minutes to process my Emlid Reach RS surveys and then export the CSV file for Pix4D.  I highly recommend EZsurv.  They now have a utility that converts the ReachRS survey file (csv file) and the UBX log file into an XML file that EZsurv actually uses to process from.  It is VERY nice and very easy.  I will double check the price and post back.  I am going to do a Youtube video on my GCP process so that other folks who are not surveyors and need to do GCP's will have an easy start :)

I now only use the ReachView app to do the survey.  Very straight forward and simple.   So steps are:

1. Survey in field with Reach RS using Reachview app. (with log capturing for at least 20 minutes)

2. Go back to office and connect Reach RS to office wifi.

3. Connect to Reach RS via web browser (same office wifi)

4. Export Survey file and UBX log file to my PC

5. Use EZsurv conversion utility to create XML file from survey CSV and UBX file.

6. Open EZsurv and drag XML file into software.

7. Click on AutoProcess

8. Export results in CSV file that you can use in whatever mapping software you use.

Quick and easy

Thanks for the fast reply Tim. So is it post processed base data so you have corrected map co-ordinates? Or it just converts the LLH to a local co-ordinate file? Cheers.

That is correct.  It is post processed data.    You need to log the ReachRs for at least 20 minutes.  If you get it out and start logging as soon as you get the job site to fly, then it can be logging while you are flying and then when you are done you can survey the GCP markers.  I have 2 Reach RS units but since the data is being post processed, I only need to only use a single unit.

We're curious at my surveyong firm to get into drone technology. Can you actually define smooth curbs, flowlines and roads with them now?

When done correctly, you are creating a 3D model with CM accuracy with a great amount of detail.  It is actually amazing what you can do with them.  I am learning constantly and there will be aspects of surveying that a drone can not replace. 

You can create outstanding 3D or 2D maps with great accuracy.  They key is getting or using good software along with quality data for ground control points (or RTK for guys going that route).  The industry leader for software is Pix4D.  You can either buy the software outright or pay a monthly fee.  The company DroneDeploy is another one that people use alot and all the processing is done online but they are actually using the Pix4D engine to process the images.

Here is a link to their training videos: https://support.pix4d.com/hc/en-us/articles/214483743#gsc.tab=0

You can do a month long trial.  You guys already have the survey equipment and knowledge.  You could start using a Phantom 4 Pro and provide some awesome solutions for clients.

Where it does not shine is areas with heavy cover (trees in Summer).  That is where Lidar steps in and over the next 2 years you are going to see Lidar really explode in the drone industry.  The price is going to keep dropping to a point where many people can start using it on drones like the P4 or other non DJI drones.

The sites to look at:

www.Pix4D.com (the industry leader)

http://agisoft.ca/ (alternative to Pix4D but not as good)

www.DroneDeploy.com

www.mapsmadeeasy.com

This is a basic but decent article on drone mapping:
https://www.dronepilotgroundschool.com/drone-mapping-software/

Hope this helps.

  

As mentioned before, PIX4D, PHOTOSCAN Pro and CONTEXT CAPTURE from Bentley are probably de facto industry standard nowadays. You have an emerging trend in Open Source softwares that will pop up soon as well. Now you have to realize that getting all the objects and topology, lines and polygons ... you will have to "vectorized" yourself from the 3D models or orthophoto's. The good point is you can do in your office. You have also to check "what it is" and to a complement survey if your customer is looking for ground definition of buildings for instance. All these were well known by the photogrammetry agencies. Interesting enough is the whole working flow process can be organized in an industrial way. You define your specifications and requirements, you hire companies to do the flight, you transfer the images in India, Pakistan or China and within a short time you get your products delivered. I am certainly not saying that's a way to go ... but keep in your mind that's the way big agencies are doing. Now we are having here in Belgium more and more surveyors handling UAV and that's just a great extension to our survey tools. So you should give a trial ! You can use a DGI Phantom 4 and a trial version of any processing software to make your mind ... or just use your smartphone camera ! The real revolution is in the image processing. UAV is simply take your camera in the air but you can also use a crane or any elevator ... Just so exiting isn't ?

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