DGPS with Arduino

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DGPS with Arduino

Postby marcusbarnet » Fri May 18, 2012 11:51 am

I'd like to try to use DGPS in order to locate my mobile robot (which can randomly move in a wide area, outdoor) and to let him return to a fixed position when I send him a specified command.

Is this possible with Arduino?

I've read something about the DGPS, but I didn't understand if I have to setup my fixed gps positions or if it is supposed to use the global ones (and in this case, I should only create the return fixed position).
Does I have to find a particular GPS sensor or every gps sensor can do this work?

Do I have to directly implement a software to calculate the distance between the fixed positions and my robot, or is there any arduino library?

Thanks for all your suggestions!
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Re: DGPS with Arduino

Postby marcusbarnet » Fri May 18, 2012 11:51 am

I've found this sensor:
http://www.sparkfun.com/products/163

Do you think it can work with Arduino?

I've read from the datasheet that when it is set to differential mode, it directly provides differential data, so I only have to read the data, I think. Is this correct?
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Re: DGPS with Arduino

Postby fll-freak » Fri May 18, 2012 12:05 pm

DGPS needs a bunch of different parts to make it work. The reason for it in the first place is to remove dynamic ever changing errors due to atmospheric errors in the GPS signal propagation. It years past it was used to remove the Selective Availability signal added by the military to make GPS less accurate.

Do get around these problems, you need a base station at a known surveyed location with a GPS that computes the location. The difference in position is the error and must be broadcast (normally by RF) to other mobile GPS systems. Those system computer their location and then modify it with the corrections received over the RF link.

The GPS unit you linked to can process correction messages on its secondary RS-232 port. But it does not include the RF receiver to pick up the correction signals. You also have to be in a place that is withing ear shot of an RF base station broadcasting the correction signal unless you want to broadcast your own correction signal.

More modern GPS units implement something called WAAS. This is like DGPS but the signal is broadcast by a satellite and is picked up by the GPS module itself. For best accuracy without breaking the bank (a DGPS receiver can cost over USD $1,000) get a GPS that does WAAS such as (http://www.sparkfun.com/products/8975).
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Re: DGPS with Arduino

Postby marcusbarnet » Sat May 19, 2012 2:11 am

Thank you for your suggestion!

Can you explain me something more about the WAAS system, please?
I read that it has a best accurancy than the DGPS, so I think it should be better to use it.

Should I have to but two WAAS gps (like the one you suggested on sparkfun) and than I have to mount one on my mobile robot and another one on the fixed base? Than, mobile robot has to continously send data about its position to the base and the base send back the correction data to the robot, is it correct?

But, what's the difference between using WAAS module or the standard one in this kind of configuration?

Can the module you suggested work fine with Arduino?

I never used GPS module, is this any document which can help me to manage GPS acquired data in order to know how to use them for the robot navigation?
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Re: DGPS with Arduino

Postby fll-freak » Sat May 19, 2012 5:25 am

The WAAS enable GPS I linked to was only one of several that are sold by SparkFun or by others. It was not a suggestion but rahter an example. You will need to look at all the features to decide what is right for you. I think it is safe to say that all the SparkFun GPS modules could be used with an Arduino.

A WAAS enabled GPS does not need anything else to make it work. You only need the single module for your mobile platform.

There are any number of documents, examples, and projects that use GPS that can be used to learn from. Just make sure the example matches your receiver. GSp modules have numerous data formats they send data and take commands in. Anything from the NMEA, TPSI, other text and binary formats, and GPS-ICD-153 for military GPS modules. For your case, I would stick with NMEA and use the Arduiino GPS module to decode these text messages.

I think I would take exception to DPGS not being as good as WAAS. If you are very close to the DGPS base station, it has to be better than WAAS. But on the average across the country, WAAS is likely better.

Forgive me, but your use of English seems just off. If you are outside North America, you need to look at the coverage maps (like here http://www.nstb.tc.faa.gov/RT_VerticalP ... nLevel.htm) to see if WASS covers your area. If not, DGPS will be needed and then you need to decide what DGPS systems are installed in your area and what receivers are available to pick up the RF broadcast and send the correction message to your DGPS enabled receiver.
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Re: DGPS with Arduino

Postby Mee_n_Mac » Sat May 19, 2012 2:13 pm

Just how close to "home" do you expect your GPS robot to get ? Depending on conditions and time of day and location you could end up just meters away or perhaps 10's of meters. To get closer than this you'll need some close range, terminal phase guidance system, like beacon of some sort.
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Re: DGPS with Arduino

Postby stevech » Sun May 20, 2012 11:23 pm

you can receive differential correction data via WAAS (built into many GPS receivers) or via the equivalent in Asia and the EU, or you can receive it via the Internet (some University as I recall). Updates very 20 minutes or so deal with the propagation error corrections.
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