GPS Uni Project, Info needed

TonyBurn · Occasional Visitor Joined: Nov 13, 2003 Posts: 6

Hi I've been browsing the forums for the last couple of weeks. I'm in my last year of unversity studying at Swansea Institute of Higher Education; and for my 3rd year project i decided to create a system which will direct a tractor driver where he is to drive in the field, this is so he can create perfectly parallel tramlines up and down the field when spraying or spreading fertiliser. I am VERY new to gps but have picked up a lot of infomation in the last few weeks in that i understand the difference between normal GPS and differential GPS and mobile differential GPS, I also understand that all GPS receivers can communice with a PC host using the NMEA protocal. Here is a copy of my feasibility study which is hosted on my webspace:

http://www.timrees.co.uk/feasibilty.pdf

My biggest problem as far as i can see is converting co-ordinates to measurements in metres and maybe levels of accuracy could be an issue though saying that i did have a drive around a field with the gps receiver in my car the other day and it plotted where i drove very accurately.

I will be buying my own PDA and GPS receiver so any advice on some quality products that will fufill my criteria would be much appriciated along with any feedback or information which may help me along with my project.

lbendlin · Posted: Wed Nov 19, 2003 12:19 am Post subject:

Not sure what exactly you need. Please be more specific.

You have already gone through the accuracy loop - that's good. So you know that despite DGPS you have to expect day-to-day deviations in the positioning. You probably also know that altitude is even more difficult to get right. So best would be if you could ignore altitude in your measurements

As for the other two dimensions - If you can assume them to be flat then this simplifies the calculation model again. And if you are just looking at a small field size (minutes rather than degrees) then you can easily convert lon/lat into meters and neglect the inheritent .

Just go out to a square field. go to two opposite corners, note down your lon/lat, and off you go. If you give your coordinates here we can help you to find the average size of a lon/lat minute at your location
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Dave · Posted: Wed Nov 19, 2003 7:24 am Post subject:

For the PDA/GPS you can't go far wrong with the iPAQ 2210, it's a great Pocket PC, small and works really well with GPS. For a GPS, it really depends whether you want a cabled setup, CF card setup or Bluetooth setup. All have their pro's and their con's, personally I prefer Bluetooth and cabled, and I always hover between the two switching between one and the other.

Maps depends really on where you're looking to go, whether you want to stay in mainland GB or wheter you want to travel to Europe. Cost is also an issue, TomTom Navigator 2 is the cheapest and looks the best, you then get CoPilot, SmartST Pro (Navman) and Destinator (PowerLOC) these generally provide European based maps and work out cheaper in the long run for european maps than TomTom.

BTW, your PDF is the wrong URL, we get a 404 not found message back.

TonyBurn · Occasional Visitor Joined: Nov 13, 2003 Posts: 6

sorry about the url i'm glad it was pointed out as i didn't notice it was wrong, the correct URL is:

www.timrees.co.uk/feasibility.pdf

That feasibility report identifies everything what I entend to do with reguard to my project.

My biggest problem at the moment is the issue of converting co-ordinates to a measurement in metres, I'm no geologist but wandered whether there is any set way of doing this??

Yet again any replies reguarding this would be much appriciated.

Skippy · Posted: Fri Nov 21, 2003 12:33 am Post subject: Re: GPS Uni Project, Info needed

There are a few things to remember about GPS. Although it is only accurate to within about 25 feet, the relative accuracy of one position to another is very good. So if you mark a spot and move 50 feet on one direction then it will give you a very accurate measurement of the distance moved. The accuracy is also very good if you mark a spot and then come back to that spot within a short time.

There is a fairly simple way you guide your tractor driver.

With software like Fugawi, Ozi Explorer or GPSMapEdit you can load a scanned aerial photo of the field (see if you can get one from streetmap.co.uk). Then you can mark waypoints on the photo exactly where you want the tractor to make the turns then link these points together into a "track log" in a zig-zag pattern across the field.

Mark the start and end points in the 4 corners of the field and then write a program to calculate the position of a the turn points spaced at the correct distance apart and from these points, create a track log for your tractor to follow. Save this track log on your GPS and then follow it's directions! (To find the conversion between meters and degrees, mark a couple of waypoints on your GPS and get it to tell you what the distance between them is and use this as a conversion factor for your program).

I would suggest that you prototype the system on a Pocket PC (you know you want one!), though I don't think it would be too practical for everyday farm use. For a production version, you could consider something like Garmin's Geko 201. It's small, simple, robust, waterproof, (don't know about farmer proof?) and it only costs about £125 http://www.garmin.com/products/geko201/ (Warning: the cheaper Geko 101 has no PC serial port so isn't suitable!)

The Geko (or pretty much any GPS) will play back the track log you have created, show you a compass heading to follow, tell you when a turn is coming up and keep you on the straight and narrow. You can create routes for different fields and different tractors using photos on your PC and upload them to the GPS where you select the correct one for the job at hand.

The next task is to make an autopilot for the tractor! 8O 8)

Good luck!

kartracer · Posted: Fri Nov 21, 2003 10:09 am Post subject: Re: GPS Uni Project, Info needed

TonyBurn · Occasional Visitor Joined: Nov 13, 2003 Posts: 6

Thanks for the reply Skippy, its all helping me piece togther what i need to do, first thing i think is to create a java class file to interpret what i need to extract from the NMEA messages send out from my GPS receiver.

As far as purchasing a PDA is concerned I have spent the last week looking at most on the market including Toshiba, Dell and IPaq. I want the chosen receiver to be bluetooth so i can use it to communicate with both my laptop and mobile phone. As far as GPS is concerened i'm currently borrowing a Motorola 12 channel receiver from the university which has an rs232 interface. The PDA i'm looking to buy is the Ipaq 2210 which was also the one recommended to me in an earlier post, I read somewhere i'd be able to plug rs232 devices into it with a serial sync cable, is what i've read correct? and does this sound like the perfect PDA for what i want?

BTW does anyone here know much about J2ME?

cheers in advance.

TonyBurn · Occasional Visitor Joined: Nov 13, 2003 Posts: 6

Oh well i took a giant leap in life tonight and ordered an Ipaq h2210 and a 512 CF memory card from www.globalpositioningsystems.co.uk. It should take a maximum of 4 days to arrive so hopefully will be in my hands by the end of the week, i just hope i don't regret buying it!

lbendlin · Posted: Tue Dec 09, 2003 1:20 am Post subject:

You won't regret it. The 2210 is a great little machine!
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TonyBurn · Occasional Visitor Joined: Nov 13, 2003 Posts: 6

What do i need for my 2210 in order to connect an rs-232 device to it? It has the same connector underneath then another type of ipaq doesn't it?

lbendlin · Posted: Tue Dec 09, 2003 11:26 pm Post subject:

it's the same connector as the 38xx/39xx and 5xxx series. You can buy the connectors at some of the online shops that carry PDA cables, or directly at www.ipaqparts.com
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TonyBurn · Occasional Visitor Joined: Nov 13, 2003 Posts: 6

Cheers lbendlin, i'll see about ordering one this week once i receive the ipaq.

chime · Occasional Visitor Joined: Mar 18, 2005 Posts: 9

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