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 USB Bluetooth module with PPP and RTK-ready
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micmail

Italy
26 Posts

Posted - 28 févr. 2012 :  09:55:15  Show Profile  Visit micmail's Homepage  Reply with Quote
To whom it may be interested,
I am designing and assembling GNSS receivers for applications with special requirements.
The last object I am working on is a USB+Bluetooth data-logger module with uBlox NEO-6P, which features PPP (Precise Point Positioning) and has high-quality carrier phase measurements for low-cost RTK projects.



I developed in collaboration with optimalsystem.de
It is called Rappen10LogBt, feel free to check it out here and ask more details either to me or my partner!

Cheers,
Michele

Edited by - micmail on 28 févr. 2012 10:02:11

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Hurston

30 Posts

Posted - 04 mars 2012 :  22:38:41  Show Profile  Reply with Quote
Hi Michele,

I've been following your blog, and this is just the sort of thing I am after. I noticed that you mention RTKLIB in conjunction with this. I assume that the unit will not receive corrections currently, but RTKLIB will be able to take care of that. I also assume that the unit will not be able to generate RTK corrections until RTKLIB can generate them. Good work Michele, it is just this sort of mid-range device that the market needs, with both the low and high ends being saturated, with nothing in between.
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micmail

Italy
26 Posts

Posted - 04 mars 2012 :  23:16:43  Show Profile  Visit micmail's Homepage  Reply with Quote
Hi Hurston,

Thank you very much for the kind words... the idea came from the creators of optimalsystem... I just generated the design.
The module is very simple and intended for people wanting to achieve sub-meter accuracy on their smart-phones and tablets in standalone mode.
It gives also a chance of logging RAW measurements in order to post-process them with RTKLIB.
There are a couple of routes I am investigating now:
- porting RTKLIB core to Android/iOS/Windows so that users can run it on their devices using a wireless module like our as slave
- developing a smarter handheld that runs RTKLIB

I am more oriented towards the first one, but I would be curious to listen to other people's opinions.

I also created another module with the NV08C-CSM which represents the natural upgrade from uBlox.

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Hurston

30 Posts

Posted - 10 mars 2012 :  15:00:54  Show Profile  Reply with Quote
My vote would be for Android, but then I'm biased towards that platform. I think Android is more for the geeky technical types that would want such a device, whereas iOS users would not be too fussed about accuracy.
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jlferreira

6 Posts

Posted - 16 mai 2012 :  20:35:56  Show Profile  Reply with Quote
Hi Michele,
I'm developing a Android software to use with GPS and I need sub-meter accuracy.
Unfortunately, I didn't find a low cost GPS device with USB interface yet.
I'd saw U-BLOX NEO-6P, that delivers this accuracy, but, it's developer kit is very expensive.
Fortunately I found this forum.
Maybe your project can fulfill my needs.
My first idea is to connect to the GPS device via USB and receive it's data in NMEA format.
Is this possible with your project?
May you send me more information about you projects?

Regards,

Jefferson.

Edited by - jlferreira on 16 mai 2012 20:43:44
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micmail

Italy
26 Posts

Posted - 16 mai 2012 :  21:29:58  Show Profile  Visit micmail's Homepage  Reply with Quote
Dear Jefferson,

I spend a lot of time searching for good inexpensive tools to provide users with high accuracy or other "special" features. All of this is of course enabled by RTKLIB, a free open source tool that processes RAW measurements output by some receivers.
The case of NEO6P is a little different in the sense that uBlox has put a PPP algorithm into their baseband in order to provide better accuracy for low-dynamic applications. The slight drawback is that RTCM input is disabled so one cannot do DGPS with NEO6P yet. On the other hand RXM-RAW and RXM-SFRB are enabled so you can do carrier-phase ambiguity resolution :)
Does this answer your curiosity for now?

Best wishes,
Mic


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jlferreira

6 Posts

Posted - 17 mai 2012 :  02:30:11  Show Profile  Reply with Quote
Hi Michele,
Thanks for the answer.

Indeed, my doubts changed as I saw your blog (you can find my comment/question there).
I saw the comparison of the modules: Rappen10, Yuan 10 (I saw Yuan20 in onetalent-gnss) and Rappen10, and I became very interested.
I saw your newer post about the Newsky TV28T too, and it interested me more than others (by the price), but if I understood, this must be used with a RTK base.
The Rappen10 (u-blox), instead, can be used stand-alone.
Am I right?
As I said, I'll need to comunicate with the GPS with an USB interface, and, for now, read Nmea Sentences. Does any of this devices can do this?

Thanks again,

regards,

Jefferson.
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micmail

Italy
26 Posts

Posted - 17 mai 2012 :  09:30:37  Show Profile  Visit micmail's Homepage  Reply with Quote
HI Jefferson,

I will reply to your email here so everyone in the forum can get a small clarification about the tools and techniques I use.
GPS L1 C/A signal is the product of 50Hz navigation data, a 1023 kchip/sec spreading code, and a 1.575MHz carrier.
The spreading code is a gold code periodic of 1ms (1023 chip, 300 kilometres). Each chip is roughly 1us (300 metres). The carrier is a sinusoid (intrinsically ambiguous of one full clock cycle) with a wavelength of roughly 3e8 / 1.575e6 = 19 centimetres.
From the signal specifications one can see that code has poor accuracy but small ambiguity, whereas carrier has high accuracy but also significant ambiguity.
To achieve <10cm accuracy one (normally) needs to use the carrier.

The main errors that influence the accuracy are:
1) satellite broadcast orbit and clock errors (respect to the truth)
2) receiver errors
3) atmospheric errors (model against truth)
4) multipath

Depending on your experiment conditions the contribution of the values above can change. Satellite orbit and clock are are usually in the order of a few metres. During a day of intense solar activity, atmospheric errors will be very high (even a few tens of metres). In urban or indoor environment, multipath will be very high (even a few tens on metres). Minimal multipath can also be experienced if your antenna has a poor radiation pattern, e.g. is omnidirectional and will pick up satellite signals bouncing on the ground.

The receivers I sell have the special characteristic of delivering carrier phase measurements. With carrier phase you can do a couple of things:
- try to solve the phase ambiguity (19cm) in standalone mode
- try to solve the phase ambiguity in differential mode

In standalone mode (PPP) you need to model very well atmospheric errors (typically using a multi-frequency receiver) and use orbit and clock information as accurate as possible. IGS provides precise products with different latencies/accuracies against the standard broadcast products.

In differential mode (RTK) most errors cancel out in doing the difference because they are common to both base and rover so the process of solving the carrier ambiguity is much easier.

To come to your questions:

Newsky TV28T has nothing to do with high precision GPS. My blog post discusses three topics, all conceptually separate. Newsky TV28T is a nice tool to digitise the antenna signal but its poor crystal prevents quality processing of GPS.

Rappen10 can be used in standalone mode but also provides carrier phase so fits well with the others (is RTK enabled).

All my receivers also output NMEA as an option of course, but none of them will achieve decimetre accuracy in standalone mode (not even NEO6P).

Accuracies of <20cm in standalone mode can be achieved only if you wait a long time in clear sky conditions. Long means a few hours with a multi-frequency receiver (which can estimate atmospheric errors) and several hours with a single frequency receiver (which can be speed up a little by using SBAS).

In differential mode accuracies of <10cm can be achieved in around 10 minutes (depends on environment, baseline length, and quality of your equipment).

Of course the above is not the GPS bible, applications must be evaluated in a case by case scenario, but a lot of it is true in theory and by personal experience.

Cheers,
Mic
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jlferreira

6 Posts

Posted - 17 mai 2012 :  12:31:38  Show Profile  Reply with Quote
Hi Mic,

Thanks for the lesson.
You clarified a lot of doubts with this post.

What is the best accuracy that I could acquire in stand-alone mode in around 10 minutes?
Yuan20 is best then others to do that or is still the Rappen10 the best choice for stand-alone?
With best I mean, the better accuracy with less time.

About my environment, I live in Brazil. The temperatures variates from -10 (southern) to +48 celsius degrees (central-west), from days to night.
In my region, the middle temperature is +35 celsius degrees at daylight.
I'll work with the specified antenna at top of the vehicle. Always in open fields.
The sky is almost all days in open conditions, but we have 3 months that are the rain periods.
This conditions vary a lot from region to region in Brazil, but this above is the reality in my region.
I will work with max speeds of 15km/h.

There are any option of low cost RTK base?

Again, I'm grateful for your help and attention.

regards,

Jefferson.
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micmail

Italy
26 Posts

Posted - 17 mai 2012 :  13:40:35  Show Profile  Visit micmail's Homepage  Reply with Quote
Hi Jefferson,

I wrote a nice long reply and was about to submit it when my boy clicked on something and closed the reply window :(

Anyway, IMHO Rappen10 is the best choice for standalone (real-time and post-processing) absolute positioning.
Relative accuracy to a reference point is differential so I assume you don't want that.

The NEO6P datasheet states better than 1m CEP50 with PPP+SBAS and clarifies:
"Demonstrated under following conditions: 24 hours, stationary, first 600 seconds of data discarded. HDOP < 1.5 during measurement period, strong signals. Continuous availability of valid SBAS correction data during full test period."
Probably it is a bit conservative to avoid legal issues.. but close to theory and my experience.

A dual frequency receiver will cost one or two orders of magnitude more than NEO6P without adding too much to real-time standalone absolute accuracy in 10 minutes.

Of course if you can record 10minutes of raw observations and post process them (either standalone or against a virtual/real base) it's a whole different story and we can talk again centimetres for absolute accuracy.

As I showed many times, relative accuracy between two receivers is easier to achieve and I demonstrated better than 5cm in 10 minutes in near to perfect conditions with all the receivers I used.
A RTK base can also be another low cost receiver with carrier phase output (after having surveyed the antenna position).

All the best,
Michele


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jlferreira

6 Posts

Posted - 17 mai 2012 :  14:09:55  Show Profile  Reply with Quote
ehehehehe...
My son (2.5 years old) sometimes does this too.

Again, thanks for all our attention.

I'd already saw the NEO-6P datasheet, but, as I never saw one in action, I think that this could be better in real world.
I do not see any problem in collect 10 minutes of data in field before start working.
As I don't know how to do, the post processing worries me. What Will I need to do?

The best scenario is a stand-alone device (even if I need collect 10 or 15 minutes of data in field) that do all the work (including the post processing). I think that may involve some programming work, and I do not have trouble with this. I could create a process that start collecting data and after a delimited time or accuracy, tells the user that he can initiate its work.

The another option, a low cost RTK is viable too. If the costs are really very low.

Tell me about how to do this two options.
In the first, how could I acquire centimetres of accuracy?
What is the product that I will need and how could I do that?

The second option, a low cost RTK.
What do I need to, to "create" this base?
How could I do that?

This is getting more and more interesting.

regards,

Jefferson.
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micmail

Italy
26 Posts

Posted - 17 mai 2012 :  22:32:42  Show Profile  Visit micmail's Homepage  Reply with Quote
Hi Jefferson,

It does look like your work has similarities with the one of my friend working at optimalsystem.de
He also uses the NEO-6P for precise low cost standalone surveying with the option of logging the raw data to then achieve cm accuracy in post-processing at the back office. Maybe you should consider discussing your application with him too as he is already quite advanced in his development.

To answer your questions.. if you can tolerate 1m accuracy in real time and <10cm after some time (e.g one day) then NEO-6P is a good choice.
You can use the NMEA for a coarse real-time positioning and store the binary messages RXM-RAW and RXM-SFRB into the laptop. When you get back to the office you can convert your logs with RTKCONV into Rinex format and process them with RTKPOST.

You have two options:

1) to produce a more accurate fix using single frequency PPP

This is the table of available IGS products:
http://igscb.jpl.nasa.gov/components/prods.html
so if you wait 3-9 hours you can download precise orbits, clocks, and atmospheric data.

2) to use a base and do a differential positioning respect to that

In this case most errors will be in common between base and rover and cancel out. Note that this can be done also in real-time using for example RTKNAVI and radio modems to connect base and rover.

For RTK you don't necessarily need NEO6P, you can use any pair of receivers with raw data. There are some on LEA-4T on dhgate.com for 35USD...
Receiver 1 is "base", stationary with a good antenna and clear sky. You collect (only once in your life) several hours of raw measurements and calculate its position using PPP. Then receiver 2, your "rover", can do RTK respect to the "base" in real time or post-processing and achieve a position that is accurate to <10cm respect to the base within 10 minutes (if rover also has good visibility and base is not far away).

I hope this explains enough.. I don't think I can go any further without stealing time to my paid work.

All the best and good luck,
Michele
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jlferreira

6 Posts

Posted - 17 mai 2012 :  23:42:28  Show Profile  Reply with Quote
Hi Michele,

Thanks for your attention and patience.

Can we continue this conversation by e-mail?
I'll send one to your enterprise, but if you prefer to continue here, please, tell me.

regards,

Jefferson.
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jlferreira

6 Posts

Posted - 18 mai 2012 :  00:24:12  Show Profile  Reply with Quote
Michele,
I sent an e-mail to your enterprise, and really hope that you answer.

regards,

Jefferson.
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Almeida100

Azores
1 Posts

Posted - 22 août 2012 :  00:25:57  Show Profile  Reply with Quote
[i}For RTK you don't necessarily need NEO6P, you can use any pair of receivers with raw data. There are some on LEA-4T on dhgate.com for 35USD...[/i}
Curiously, there is still godd’old GPS engines available, like SUPERSTAR IIs , JUPITER 21s and the like, on http://rtkgps.webs.com/ !
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suhasg

Germany
1 Posts

Posted - 04 déc. 2012 :  18:19:11  Show Profile  Reply with Quote
quote:
Originally posted by micmail

if you can tolerate 1m accuracy in real time and <10cm after some time (e.g one day) then NEO-6P is a good choice.
You can use the NMEA for a coarse real-time positioning and store the binary messages RXM-RAW and RXM-SFRB into the laptop. When you get back to the office you can convert your logs with RTKCONV into Rinex format and process them with RTKPOST.



Hi Michele,

Its been 6 months since the last post here, but this is the page where I found pertinent information to the questions I had. So I couldnt resist but ask you one more.

Can I use RTKCONV-RTKPOST with logs from standalone Neo6P or do I need a basestation-rover model?
I looked at RTKNAVI documentation and it expects to specify the paths to both the base station stream and the rover stream. Is there a work around for this or is it impossible to use RTK with a standalone NEO6P GPS receiver.

(https://www.optimalsystem.de/os.aspx?x=4112&lg=en) - This is the product I have in mind.

I am expecting to achieve submeter accuracy. I would always have the laptop during the measurements, so I can run the postprocessing in realtime. Also I am planning to use the RTKLIB from within Matlab as a part of my main program. Would this be possible?
And do I need any downloaded database of correction data to be used with RTKlib?

Thank you.
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