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| T O P I C R E V I E W |
| micmail |
Posted - 28 févr. 2012 : 09:55:15
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 |
| 15 L A T E S T R E P L I E S (Newest First) |
| raghurama |
Posted - 13 janv. 2013 : 07:55:21
quote:
Originally posted by micmail
@suhasg
As I mentioned before, you could use NEO6P raw measurements and run a single-frequency PPP with precise products(e.g. using RTKLIB when it will support it). This cannot be done in real-time or near-realtime as precise products take a while to be available. Any other high-accuracy setup would be differential and need a base station.
@raghurama
I managed to run RTKLIB sources on ARM9 with ArchLinux but I am not an Android expert.
RTKLIB sources compile easily with gcc so I imagine that building a basic library to call within your Android app should be quite easy using NDK. At the end, you should only need to handle communication classes which are OS specific.
Hi Michele,
Thank you so much for quick reply.
I have some porting knowledge(NDK Porting) on android platform and at the same time iam new to RTKLIB,I just downloaded RTBLIB bins from RTK website they are just running sample input streams and showing graphs on screen.But here iam planning to use same library in android.I can Port entire RTKLIB on Android platform using NDK. After that i dont know what to do.Could you please Provide your valuable answers for following questions:
1. Do we need Any hardware to get Input streams
2. How to plot Graphs on Android
3.can we use existing GPS on android
4.Could you please Provide Any sample application.
5.Can you suggest sample POC(I need to develop sample Application) on android using RTKLIB.
4.Please Guide me proper way this is very important for my project.
Thanks & Regards
Raghuram |
| raghurama |
Posted - 13 janv. 2013 : 07:51:24
Hi Michele,
Thank you so much for quick reply.
I have some porting knowledge(NDK Porting) on android platform and at the same time iam new to RTKLIB,I just downloaded RTBLIB bins from RTK website they are just running sample input streams and showing graphs on screen.But here iam planning to use same library in android.I can Port entire RTKLIB on Android platform using NDK. After that i dont know what to do.Could you please Provide your valuable answers for following questions:
1. Do we need Any hardware to get Input streams
2. How to plot Graphs on Android
3.can we use existing GPS on android
4.Could you please Provide Any sample application.
5.Can you suggest sample POC(I need to develop sample Application) on android using RTKLIB.
4.Please Guide me proper way this is very important for my project.
Thanks & Regards
Raghuram |
| raghurama |
Posted - 12 janv. 2013 : 18:22:13
Hi All,
Could anyone please provide me information regarding RTKLIB porting on android platform and what are the basic things required to port RTKLIB on android.Please help me
Thanks in Advance
Regards
Raghuram |
| micmail |
Posted - 12 janv. 2013 : 18:13:39
@suhasg
As I mentioned before, you could use NEO6P raw measurements and run a single-frequency PPP with precise products(e.g. using RTKLIB when it will support it). This cannot be done in real-time or near-realtime as precise products take a while to be available. Any other high-accuracy setup would be differential and need a base station.
@raghurama
I managed to run RTKLIB sources on ARM9 with ArchLinux but I am not an Android expert.
RTKLIB sources compile easily with gcc so I imagine that building a basic library to call within your Android app should be quite easy using NDK. At the end, you should only need to handle communication classes which are OS specific. |
| raghurama |
Posted - 12 janv. 2013 : 18:02:06
Hi Michele,
Could you please provide me information regarding RTKLIB porting on android platform and what are the basic things required to port RTKLIB on android.Please help me
Thanks in Advance
Regards
Raghuram |
| suhasg |
Posted - 04 déc. 2012 : 18:19:11
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. |
| Almeida100 |
Posted - 22 août 2012 : 00:25:57
[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/ ! |
| jlferreira |
Posted - 18 mai 2012 : 00:24:12
Michele,
I sent an e-mail to your enterprise, and really hope that you answer.
regards,
Jefferson. |
| jlferreira |
Posted - 17 mai 2012 : 23:42:28
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. |
| micmail |
Posted - 17 mai 2012 : 22:32:42
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 |
| jlferreira |
Posted - 17 mai 2012 : 14:09:55
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. |
| micmail |
Posted - 17 mai 2012 : 13:40:35
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
|
| jlferreira |
Posted - 17 mai 2012 : 12:31:38
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. |
| micmail |
Posted - 17 mai 2012 : 09:30:37
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
|
| jlferreira |
Posted - 17 mai 2012 : 02:30:11
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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