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744 posts

Ultimate Geek
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Topic # 89193 27-Aug-2011 20:52
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I need to search for my boundary pegs. A surveyor wants to charge me way too much for the job, IMHO.

Then I thought, "Hey. I wonder if I could do the job myself using a GPS device and a survey map?"

What do you think guys? Possible? I know nothing about GPS gadgets but it seems it might be cheaper to buy one (that I could later use in the car) than to pay an inflated price to a surveyor.

Note that I'm not trying to resurvey my section, just locate some pegs that have become overgrown or buried under debris.

Cheers :-)

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1579 posts

Uber Geek
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  Reply # 512959 27-Aug-2011 21:06
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Standard GPS available to us mere mortals is really not very accurate, survey people use a device which acts kind of like a local base station for much more accurate locations (hence the price).

Now you can use your GPS to locate the boundary pegs, but should a dispute arise there would be a problem proving the accuracy of your survey.
 

148 posts

Master Geek
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  Reply # 512963 27-Aug-2011 21:22
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Agree with gregmcc, common GPS is not accurate enough. You will have better success with a map, compass & tape measure.

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  Reply # 512964 27-Aug-2011 21:24
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Consumer GPS devices are not accurate enough for topographical surveying. I believe you also need to reference the point on the NZ Map Grid to be relevant. If you can't locate the pegs and need to get them replaced then you will need a qualified surveyor to do that for you to be legal.

If you can find one, or better any two pegs, you should be able to find the remaining using a basic tape measure and the section plan (available from the council).




Always be yourself, unless you can be Batman, then always be the Batman



57 posts

Master Geek
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  Reply # 512972 27-Aug-2011 21:54
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Assuming you have the plans and a standard size residential section I think you will have more joy using a tape measure. Minimum inaccuracy of a 'consumer grade' GPS is 4-5 m.

If you have a lifestyle block then a GPS may help, provided you have the coordinates of the pegs.

Your biggest problem may turn out to be missing pegs...

Cheers,
Peter.

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Ultimate Geek
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  Reply # 512973 27-Aug-2011 22:04
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Just an FYI, "Common" GPS is no different to the military ones on accuracy, This feature was turned off in 2000.

But for what you are trying to do I'd pay the guy, It's not worth the hassle




Most problems are the result of previous solutions...

All comment's I make are my own personal opinion and do not in any way, shape or form reflect the views of current or former employers unless specifically stated 

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Master Geek
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  Reply # 512974 27-Aug-2011 22:06
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Correct, but there are also commercial GPS systems with accuracy of a few cm, but you won't find those in any shops.



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Ultimate Geek
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  Reply # 512990 28-Aug-2011 01:10
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Thanks guys, your comments are just what I wanted. Sounds like a tape might be cheaper :-)

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  Reply # 513648 29-Aug-2011 20:37
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Just to complete the discussion, surveying GPS units also measure the phase of the incoming signal to make fine incremental measurements. This results in a resolution of about 2mm. Consumer GPS receivers do not measure the phase. (Courtesy of Wikipedia.)




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Ultimate Geek
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  Reply # 522662 18-Sep-2011 15:12
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Beccara: Just an FYI, "Common" GPS is no different to the military ones on accuracy, This feature was turned off in 2000.


It is true that selective availability was turned off some years back for civilian use that does not mean as many assume that they now have the accuracy of the military ones.

The approved military users have access to differently coded transmissions of much higher "pulses" (the signal is a form of spread spectrum CDMA) per second rate resulting in higher accuracy and greater  immunity to external influences. Special military uses such as nuclear targetting may use other modes again.

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  Reply # 522684 18-Sep-2011 16:40
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John2010:
Beccara: Just an FYI, "Common" GPS is no different to the military ones on accuracy, This feature was turned off in 2000.


It is true that selective availability was turned off some years back for civilian use that does not mean as many assume that they now have the accuracy of the military ones.

The approved military users have access to differently coded transmissions of much higher "pulses" (the signal is a form of spread spectrum CDMA) per second rate resulting in higher accuracy and greater  immunity to external influences. Special military uses such as nuclear targetting may use other modes again.

Military always have, and always will have, access to greater levels of accuracy as they paid for the system.
As John has said they use a number of ways to achieve this including having full access to a second signal channel and highly encrypted dataset to compare against (which reduces inherent system errors).  
Normal consumer-grade GPS is, as has been said, good for 'repeatable' accuracies of  5-15m, and within this range for most of us our eyesight does the rest to put us 'on-the-spot'.
Higher cost equipment may 'reference' the military channel, but not decode it. And any quality unit will also accept 'corrections' via either a land based or satellite based service, depending on which you subscribe to. Using any one or a combination of these techniques you'll get reliable positions to a few hundred mm and better, depending upon how you go about it.
 

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