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  1. #1
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    Default gps plotting for event mapping

    I have spent countless hours researching GPS trying to find a clear cut answer to my problem so if anyone can help that would be amazing


    I run a large-scale event on the beach every year and we would like to record exact GPS coordinates for certain "points of interest" at our event ( ie. the corners of an event or endpoint of a fencing run. ) This would save us 2 days of remeasuring each year to locate these points of interest to begin event construction.

    From what I have found all mobile devices are not accurate enough

    and what I need is a GPS plotter that is WAAS enabled with a high sensitivity chipset installed.

    I need to be accurate up to 3 feet but I would prefer to be accurate to 1 foot.

    Is there anything else I should be looking for in a Plotter?

    Any suggestions on a certain GPS plotter that would work?

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  3. #2
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    Long Answer: 3"/1m accuracy cannot be achieved reliably at present by dedicated WAAS enabled Aviation GPS/VHF devices further enhanced with LAAS [Local Area Augmentation System] using differentially corrected signals via VHF from GPS Ground Stations around an airport, although it's expected that further refinement will result in consistent accuracy of or below 1 metre for all-weather precision approaches. Therefore it would seem unlikely that there is any 'portable' GPS/GLONASS/WAAS device available which is capable of 1 to 3" accuracy without the type of positional correction available to LAAS enabled equipment.
    Short Answer: Dunno.
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  4. #3
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    You want less than 4Mtr accuracy good luck M8 , you can go buy an Surveyors GPS system which is more accurate but is not a Public device. "Come on" the GPS system is still military base. so ya think a public based system is going to have a SA accuracy of a Foot "300mm" humm. not likely. But we all hope.
    Now that said, if you place a flag at x on the beach then place another at Y , Z.
    And it is at 4 Mtr SA so you do your stuff and finish up and is still 4Mt SA so what has changed NOTHING so this is what we have to be happy with M8.
    4 meters is a good SA coz if it's short I fall down a Big Hole out in the Gold Fields.
    So be grateful the US gives you 4 Mtr accuracy.
    Hummmmmm


    Oh and by the way Welcome to the Forum M8
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    Thank you both for your informative answers! They have clued me in a little.

    And Thank you for the welcome to the forum!

    What does SA stand for? Google told me Selective Availability? Is that right?

    What would you say is the best consumer available GPS plotting device with the highest accuracy on the market?

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    Also, kind of intrigued by how these devices work...

    If I were to walk out onto the beach and plot a point of interest with a GPS plotter, and the following year I walked back out on the beach to that exact specific point,

    will the coordinates displayed on the unit be the same as the previous year (and display the point of interest)

    --OR--

    Will the coordinates on the unit be different... (give or take X amount of metres) a.k.a. if i stand X feet to the right of the exact point it will diplay same coordinates as the previous year

  7. #6
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    SA = Satellite Accuracy.

    The coordinates of a given physical location likely will be a bit different even if checked some several minutes later. If they were the same the next year it'd be a fluke is all. Unless the exact same satellites are in the exact same position and their calibration hasn't changed of course, but that'd be a bit like winning the lottery 2 years in a row to put it in perspective.

    What about if you chose a starting spot which is reasonably accurately defined from year to year by finding it within a few metres by triangulation then used a dumpy level and laser measure for shooting the rest of the layout? Total outlay is only going to be several hundred bucks then.
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    Thanks,

    Now I would consider myself pretty technologically savvy but you have me scratching my head with the below statement.

    Quote Originally Posted by Neil View Post
    What about if you chose a starting spot which is reasonably accurately defined from year to year by finding it within a few metres by triangulation then used a dumpy level and laser measure for shooting the rest of the layout? Total outlay is only going to be several hundred bucks then.

    I am open to having a professional survey done which is what I believe you are referring to...?

    The reason we need to be so accurate is that when the construction is complete the event spans completely to the edge of property lines that local officials will not let us cross. So if one of our points is off by even a couple feet, everything needs to be remeasured.

    Also what exactly do you mean by triangulation? I understand the concept from movies but how would I go about doing something like that?

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    Certainly a professional surveyor with modern equipment and access to nearby benchmarks and trig points [fixed known geographical positions, used as certain datum to extrapolate the precise position of another nearby point or boundary] could very accurately place the entire adjoining property boundary or just one or two points on it for you. Surely the local authorities know its position anyway, or how else would they even know that you've encroached by just a couple of feet? If you haven't already i'd simply ask them where it is, maybe you'll have to pay for some petty functionary to come out and bang a stake or two in the ground.

    But paying for a survey was not what i was referring to in the post you've quoted. I mean using the type of equipment utilised by the construction industry to set out the profiles for buildings etc. Dumpy levels and associated equipment are much more basic/primitive than the modern theodolites used by the land survey industry, but for smallish areas they're very accurate when carefully used and relatively cheap and easy to buy [here at least]:
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    Triangulation has many 'levels' of accuracy depending on it's purpose and it's meaning can also vary with it's purpose. The term is used in surveying and large-scale triangulation was used extensively for very accurate surveying until recently. At the other end of accuracy it's used for course checking/relocating position during cross-country navigating. Basically as i was referring to it, it's a method of determining the position of a point on the earth or an object by shooting bearings to or from at least 3 know geographical points then using back bearings to plot 3 lines which theoretically will intersect at that point on a map or chart from which it's grid reference/coordinates can be read. Of course, the scale of the chart and the accuracy of the bearings will have great influence on the final accuracy. If the three lines don't precisely intersect they will form a [hopefully] small triangle known as 'the triangle of error' in which it can be assumed the point is located, therefore to be theoretically accurate to within 3 feet the longest side of 'the triangle of error' should be no more that that. It's most basic form is using a simple magnetic compass to obtain bearings to 3 distant hilltops or other prominent local features which have known GRs or coords, but of course precise accuracy is not important to a temporarily disorientated bushwalker who only wants to check his/her position to within a couple of hundred feet or so [or even just know which ridge he or she's standing on]. You won't get the degree of accuracy you're wanting using a handheld compass, even a very accurate military one. However, you may not need to pay a qualified surveyor with a high-tech theodolite either.
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