Low cost L1+L2 GNSS RTK receiver for Drones. North RTKite receiver.

Anton Strydom February 22, 2016 at 9:08am

Good day RPM

I hear what you say,

I am not trying to get into an argument. If you look at the data posted here it is comparing a RTK capable device to a autonomous device. The U-Blox they use for comparison is not capable of doing RTK

L1 has been shoved aside with the availability of L2/L2c and L5. What we set out to do was to produce an affordable instrument capable of locating objects such as survey pegs etc due the distances my brother has to travel and the cost involved in having to travel and the point out a few pegs 9distance from Windhoek to Rundu around 800 km and to Katima around 1500 km) Besides keeping or one of his staff members out of more productive work.

It has taken me almost 3 years to develop this unit and using L1/L2 equipment to test against.

I respectfully disagree that L1 looses its fix in less ideal situations. It is purely as I state above that with the advent of L2/L2C and L5 that L1 was disregarded and no development took place.

Why it has taken me so long to develop this unit is purely that I am funding the development out of my own pocket and do not have the resources companies have.

I will with pleasure answer any questions and assist where possible

Maybe I should as you suggest create a blog for this

Take care

Regards

Anton

Bernardo Espinosa February 22, 2016 at 8:58am

Dear Anton, the comment that RPM does is the correct point. Please comment us regarding the environment of your trials.

Please note the samples of operation that I showed under 15m high tree canopy, rainy and cloudy ionized environment, that is the commonplace on the fieldwork. As you may imagine the people that create and launch L2 capable satellites wouldn't do it if it wasn't needed.

Also consider that is better that you start your own discussion as you are still on R+D phase, and you will receive very important feedback.

Looking forward for your thread and certainly interesting data!

RPM February 22, 2016 at 8:47am

Anton,

In my experience the attraction to L1/L2 over L1 is not necessarily greater accuracy. It is rather the L1/L2's ability to hold fix in less than ideal situations.

I am sure everyone involved in this thread would be interested in learning about your product through its own blog post.

Looking forward to all developments!

Anton Strydom February 22, 2016 at 8:24am

Good day Bernardo

I am not trying to get into any argument, I had a look at my data which I will forward to you at some stage. I achieve full RTK lock in less than 60 seconds, on average around 27 seconds. This is faster thank any of the survey grade instruments I have tested. Presently I have the following L1/L2 instruments that I test the L1 GPS against

2 x Leica SRX550

4 x Geomax ZGP800 A

All the instruments connect to the same CORS base 16 km away from me

Tests are done using internet connectivity

I also have Pacific Crest radios that I use to test between the L1 and L1/L2 units

I also use a couple of 886Mh data radio that I adapted to use on the L1/L2 units to "talk" to the L1 unit and I also use them for the L1 units to talk to each other

There is absolutely no difference in accuracy between the L1 and the L1/L2 units whatsoever.

I will get hold of my brother to get the verified data from him and forward it to you

Him being a professional surveyor was very skeptical about the L1 frequency as when he first started using GPS for survey he used L1 instruments that were difficult and cumbersome to use

He however for aerial photography and accuracy is using my L1 unit with great effect

Regards

Anton

Bernardo Espinosa February 22, 2016 at 8:04am

Dear Darius Jack,

The very concept of Differential GPS or RTK, that is indeed a Diferential in real time, is basically a Binary system. And this is required exactly due to Inospheric induced error, the actual signals are indeed millimetric.

I agree with you on the time it takes to get a local point, and actually for a precise CORS setup it requires about 4 months of average readings, that is normally solved with a simple PostProcess before the actual RTK job to get a local known point at reach, to place the correcting Base. This is commonplace in surveying.

It is a pity that you cannot access free CORS, and it is worst in most countries that do not have CORS at all. We developed the AutoCaster in 2012 thinking on that problem and it renders any of our receivers into a field CORS Base, broadcasting by Cellular network in 5 minutes, very simple and stable.

I'm sorry this link is in spanish but the graphics are telling on the modes that you can use:

http://www.northtopografia.com/index.php/soporte/modos-de-conexion-rtk

L1 has been arround for decades now and the only addition has been freely available algorithms, but its gap to L2 and L5 band corrections is big.

Indeed a 2000USD receiver is not for hobbyist, it is for professional applications that are our costumers and we focus in that.

We are not good at mass market, we are very good on customs high-end solutions.

Bernardo Espinosa February 22, 2016 at 7:50am

Dear Anton, I really don't want to do an argument, but 60 seconds is still slow for our costumers. That is a systemic issue of the L1 that receives its information in batches. That said I think that you've done a great work pushing the limits of L1 RTK, that has many applications of course.

I daily get comments from our costumers that have tried and discarded L1 RTK on their own applications so I think there are two different worlds.

Darius Jack February 22, 2016 at 7:06am

@Anton,

what is a price of your RTK GPS unit ?

I would like to develop all-Internet RTK GPS ground reference offset corrections.

I don't buy the concept of twin RTK GPS kit since it takes hours to get ground based RTK GPS unit to calculate high precision geolocalizatiojn on itself.

Access to CORS reference stations is neither free or open either in EU or US.

There is no open access free CORS service provided oveer the Internet.

Exactly as in case of the first car gps navigation systems price is down from initial $2000 to $20 today, so I expect RTK GPS L1 to be offered at $100 as a single unit by the end of 2016.

Hobbyists can't afford $2000 or $200 for rtk gps buying $500 drone from DJI.

Small drone operators are interested in reliable 1m accuracy RTK GPS to work 100% time.

Drone precision landing is not supported by present GPS + controller software/hardware technology due to turbulences at the ground level so no need to buy $2000 RTK GPS.

Could you refer me to L2 ionospheric error maps ?

Anton Strydom February 22, 2016 at 4:57am

Good day Bernardo

I hear what you are saying but do not agree

1. Slow start, My gps achieves autonomous lock in under 20 seconds from power up and full RTK lock in under 60 seconds

2. As above RTK Fixed position in under 60 seconds

3. I do not have this problem at all.

4. Restart after signal loss is under 10 seconds and not a problem whatsoever

5. My system is able to connect to any system, RTCM3, CMR, CMR+, Leica

6. The system that I designed do not need any accessories besides the antennas the radio, cellular modem etc are all integral to the design

The system supports helical, ceramic patch active and passive GPS antennas

The system is capable of supporting a L1/L2 receiver and as mentioned the only thing from preventing me to implement a L1/L2 receiver is the cost as at R 16.00 to the US$ an R 17.00 to the Euro it makes it impracticable and financially not viable to implement that

Therefor I spent a lot of time perfecting my algorithms etc to make L1 work properly

As mentioned there is no difference between observations taken with the L1 frequency receiver and the L1/L2 receivers.

My brother is a land surveyor and the data has been verified by him

Regards

Anton

Bernardo Espinosa February 22, 2016 at 4:47am

Dear Ralph Pendergraph, welcome to the discussion!

Here are well seasoned UAV users that will help you to setup your drone on record time.

Cheers!

Bernardo Espinosa February 22, 2016 at 4:44am

Dear Anton Strydom

We are aware of the capabilities of the Ublox N and T series for Raw data that can be easily postprocessed of worked in RTK with the RTKLIB algorithm. We tried and discarded that way 6 years ago due to the systemic problems on L1 that users on our main markets (Surveying, professional, tactical, emergency, robotics, energy) cannot allow, namely:

1.- Slow Cold Start.

(By slow I mean up to 5 minutes compared to 1-2 seconds that the L1+L2 systems give)

2.- Slow initial Fixed position acquire.

3.- Position offsets after 90º and 180º angle turns.

4.- Slow restart after signal loss.

5.- Lack of integration with existing standard CORS; GBAS, Beacons and professional RTK.

6.- After integration with the rest of the accessories, the price difference VS the performance loss is not significant.

We have power users using our RTK receivers under a tree canopy 15m high, that started using L1+L2 receivers with L1 CORS corrections and ended up switching to all in L1+L2 signals due to poor performance. Pictures below.

Best!

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Low cost L1+L2 GNSS RTK receiver for Drones. North RTKite receiver.

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