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Differential GPS

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 14 October, 2007 » Differential GPS « Previous Next »

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paul_saunders
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Username: paul_saunders

Post Number: 1
Registered: 09-2007

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Posted on Wednesday, 19 September, 2007 - 05:24 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi folks

this is my first post so bear with me.
Most "consumer" GPS units are only reliably accurate to about 15m (despite what it says on the screen!). This accuracy can be improved by picking up correction signals from a local base station (called differential GPS). A basic GPS can be bought for AU$150 but the plug-in receiver is about AU$1000-2500 (sorry about the Aussie dollars - I am an ex-POM living in Australia). The receiver picks up the correction information by radio and adjusts the "plotted" position of the roaming GPS. This does not sound to complex to me so I was wondering if any of you electronics folk fancy looking at designs for a DIY receiver.

cheers

PaulS
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arw
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Post Number: 487
Registered: 04-2005


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Posted on Thursday, 20 September, 2007 - 04:33 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

(BTW the 'start new thread' link for a new topic is at the bottom of the main Chat Zone page --otherwise you will start a sub-thread off an existing thread.

HTH
Admin
ARW

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eagre
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Post Number: 166
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Posted on Friday, 21 September, 2007 - 02:00 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

PaulS -

First, the differential GPS transmitter must be located at a very precisely established position - this is not as easy as one might assume in many areas. Most are located at such sites as airports. Second, the GPS must be in close proximity to then differential transmitter to receive valid corrections. Third, there are few applications aside from landing aircraft and targeting munitions where the precision of differential GPS is required.

Ed
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terry
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Username: terry

Post Number: 411
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Posted on Friday, 21 September, 2007 - 08:16 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I thought they turned off the error in the GPS siglals ?

Terry
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grab
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Post Number: 557
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Posted on Friday, 21 September, 2007 - 10:12 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

http://en.wikipedia.org/wiki/Differential_GPS

Paul, your best bet is to go to Google and enter "dgps receiver". The first page shows two links to pages with homebrew projects.

Graham.
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atferrari
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Posted on Friday, 21 September, 2007 - 11:09 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

POM? What does it means?
Agustín Tomás - Buenos Aires - Argentina
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paul_saunders
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Posted on Saturday, 22 September, 2007 - 10:14 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi again folks
thanks for the replies. Yes SA was turned off in 2000, I want sub metre accuracy to plot the position of rare and endangered plants - so we can find them again and check they are healthy, I have followed the Google links which do talk about low cost DIY DGPS but the final websites are all unavailable. A POM (derogatory term for the English in Australia) I believe stands for Prisoner Of her Majesty.

So still asking if anyone can help with DIY DGPS receiver.
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xenington
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Username: xenington

Post Number: 27
Registered: 01-2007

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Posted on Saturday, 22 September, 2007 - 12:13 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Here is a question about DGPS in general.

I live in Derbyshire, which is about as far from the sea as it is possible to get in the UK, and the Trinity House DGPS stations are all located on the coast. The nearest station is at Flamborough Head - about 150km straight line distance, next is Point Lynas at 200km. According to Trinity House, both these stations have a nominal range of 277km. Do you think DGPS would work this far inland? Or would accuracy suffer too much?
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eagre
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Post Number: 167
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Posted on Sunday, 23 September, 2007 - 02:21 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

PaulS -

I see now your requirement for sub meter accuracy, but the question is: can you determine the absolute position of a DGPS transmitter you might install in the vicinity of these plants to that sub meter accuracy. This would be very difficult in many areas.

Ed
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obiwan
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Post Number: 1972
Registered: 12-2005

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Posted on Sunday, 23 September, 2007 - 02:31 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I don't know, you could probably pay somebody to come out and survey the site and give you an accurate position. At least accurate enough for what he wants.

Another question though, would be would his own site, be interfering with anything else? Hate to see him cause a plane to crash or something!!

As far as actually building one.....

I think that might be far tricker than you expected, or cost more than you would like.

The timing components etc.... wouldn't be easy to make, or cheap to purchase.
Do Not Hit The Fly That Lands On The Tigers Head.
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terrym
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Posted on Sunday, 23 September, 2007 - 06:01 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I believe "POM" is actually "Prisoner of the Motherland", as applied to convicts taken from England to Australia to serve out their sentence for crimes committed.
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grab
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Posted on Monday, 24 September, 2007 - 01:18 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

At the risk of being a whinging Pom, http://www.snopes.com/language/acronyms/pommy.asp.

(Incidentally Agustin, "whinge"=complain, pronounced "winj", and "whingeing Pom" is a particular Aussie insult directed at Brits who go to Australia and then complain about how they don't like Australia. Of course, if Australia wasn't so rough then us Poms wouldn't complain... ;-)

Graham.
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eagre
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Post Number: 168
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Posted on Tuesday, 25 September, 2007 - 01:57 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

obiwan -

The accuracy of a ground survey is only as good as the position accuracy of the monuments on which the survey is based. In most areas this is unlikely to be sub meter, and in remote areas is usually much worse. Then survey can be quite accurate relative to an accepted base monument and thus for property lines, etc., but highly innaccurate with regard to GPS coordinates.

Ed
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paul_saunders
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Posted on Wednesday, 26 September, 2007 - 05:28 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ground stations are not a problem for me. Most of the survey work will be within a few tens of kms of an existing base station that transmits the correction data continuously on 314kHz

All I am interested in is a receiver which will "correct" my Garmin Gecko GPS (this cheap little unit is DGPS ready in that it will accept NMEA correction sentences.

The established base stations are there to provide correction data for maritime users. So they are usually near the coast. The usefulness of the data they transmits degrades with distance but from my reading up to approx 100km is acceptable. Much more than this and the base station and the rover are experiencing different atomspheric interference (and hence errors) therefore the corrections are less useful.
For more background information go to http://www.amsa.gov.au/shipping_safety/navigation_safety/differential_global_postitioning_system/dgps_fact_sheet.asp

For general stuff on DGPS see http://www.land.vic.gov.au/references/publications

Without even a hint of a whinge
cheers
PaulS

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