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  1. #1
    yakka is offline Apprentice (new member)
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    Default squaring up large areas

    I usually use diagonals or 3m - 4m - 5m formula to square up.. My question is what methods do you use over large areas e.g.: 40 x 30m to ensure you get a nice perfectly set rectangle
    <O</O


    Cheers yakka
    Last edited by Daddles; 15th Dec 2006 at 09:15 AM. Reason: cleaned out some wordprocessing tags

  2. #2
    David L's Avatar
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    Good question I was wondering that my self.
    I am stuck with the 3,4,5, formula too.

  3. #3
    ozwinner is offline Registered
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    Thumbs up

    Measure the diagonals.

    If you have an odd shape, run string lines to create a rectangle and measure the diagonals of the rectangle, then take and measuements for the odd shape from that.

    Al

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    I use a surveyor.

    If you need accuracy over that sort of area, and can't handle a theodolite, that's your only solution.

    If it's farm work or whatever, you could use a GPS.

    Cheers,

    P

  5. #5
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    Sorry to disagree bitingmidge, but I wouldn't use a GPS unless you can afford to be up to 20m out (or more).
    Cheers.

    Vernon.
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    Thinking out aloud ...

    1. Mark out one corner using the 3,4,5 rule (or 6,8,10 or 9,12,15 or ...) and then use a string line from the corner and through a vertices's (sp?) to the other corner. Once you have two sides, then next two shouldn't be difficult.

    2. Measure out 30m, 40m and 50m of string/rope.
    Cheers.

    Vernon.
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  7. #7
    Chesand is offline Novice
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    Default

    5, 12, 13 also works. 5 & 12 are the sides, 13 the hypotenuse if it is sqaure
    Herbie
    "It's good enough" is low aim

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    bitingmidge's Avatar
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    Quote Originally Posted by Vernonv View Post
    Sorry to disagree bitingmidge, but I wouldn't use a GPS unless you can afford to be up to 20m out (or more).
    Ahh yes, sorry. You'd have to know a surveyor with a fair dinkum one!

    Cheers,

    P

  9. #9
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    Quote Originally Posted by bitingmidge View Post
    You'd have to know a surveyor with a fair dinkum one!
    Yep, one of those would work a treat. Very accurate bit of gear, but also very expensive.
    Cheers.

    Vernon.
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  10. #10
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    Yes, Differential GPS. Funny stuff. The US sets up the GPS system and realises that maybe an adversary may also able to use it for military purposes. Solution - introduce a secret "random" error into the system. The US navy then sets up correction signals that transmit the error corrections so you can remove the errors (later) - this is differential GPS. From memory differential GPS is accurate to about 10-20cm.

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    outback's Avatar
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    Quote Originally Posted by Vernonv View Post
    Sorry to disagree bitingmidge, but I wouldn't use a GPS unless you can afford to be up to 20m out (or more).

    Of course farmers which use gps with an accuracy of 2 cm wouldn't count I guess.
    Boring signature time again!

  12. #12
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    Quote Originally Posted by outback View Post
    Of course farmers which use gps with an accuracy of 2 cm wouldn't count I guess.
    Same system as the surveyors, not your $100 Tandy variety!

    Mind you, I've used "farmer's levels" a bit and they have a "surprising" level of accuracy!

    Cheers,

    P

  13. #13
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    Other than for cropping (mainly), there aren't too many farmers around that have/use high accuracy positioning systems.

    I'm always amazed at the number of people (not just farmers) that expect their $200 GPS received to be accurate to the metre (or sub-metre).

    Even the 5 metre accuracy most receivers quote in nearly impossible to achieve under normal usage conditions.
    Cheers.

    Vernon.
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  14. #14
    joe greiner is offline Old Goat
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    Over that large an area, a string or rope will stretch too much to provide reliable measurements. Best bet is to hire a surveyor. Alternatively, use a steel tape to measure each leg and hypotenuse. If your tape is too short, lay out a smaller rectangle at one corner, and extend its legs in the required directions. In either case, use a spring scale at the pulling end of the tape to assure the same tension in the tape for each measurement. For the shorter tape, re-check the overall diagonals by using taut string for alignment, and measure segments with the tape and spring scale.

    Joe
    retired civil engineer, but not a surveyor
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  15. #15
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    Quote Originally Posted by joe greiner View Post
    Over that large an area, a string or rope will stretch too much to provide reliable measurements. Best bet is to hire a surveyor. Alternatively, use a steel tape to measure each leg and hypotenuse. If your tape is too short, lay out a smaller rectangle at one corner, and extend its legs in the required directions. In either case, use a spring scale at the pulling end of the tape to assure the same tension in the tape for each measurement. For the shorter tape, re-check the overall diagonals by using taut string for alignment, and measure segments with the tape and spring scale.

    Joe
    retired civil engineer, but not a surveyor
    Yep and don't forget to take into account the thermal effects upon the tape as it is calibrated to give accurate results at given tension and given temperature.

    It depends upon what degree of accuracy you are after - most formwork is + - 10mm so reasonable tolerances are probably all you are after and a tape with consistent tension is most likely adequate.

    I'm with Joe
    Cheers

    TEEJAY

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  16. #16
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    Quote Originally Posted by yakka View Post
    I usually use diagonals or 3m - 4m - 5m formula to square up.. My question is what methods do you use over large areas e.g.: 40 x 30m to ensure you get a nice perfectly set rectangle
    <O</O


    Cheers yakka
    define "perfectly set rectangle"
    how much "out of square" error can you tollerate?

    and before you answer, can you tell if the area you want to plant the rectangle is on level?

    if you have a spring balance and a 50m steel or cloth tape, you can set out the rectangle because just like the 3:4:5 triangle
    30 squared + 40 squared = 50 squared (900 + 1600 = 2500 = 50x50)
    important points
    • both ends of the tape must be at the same level which is not the same as the same distance off the ground
    • the tape must not touch the ground anywhere
    • all measurements must be made with the same reading on the spring balance
    • lay out the 40m long side
    • then from one end lay out the 30m side, drawing an arc on the ground roughly where the corner should be
    • lay out the 50m diaganal – where the diaganal intersects the arc, is where the corner is
    • repeat for the 4th corner
    if you need to be accurate to a few cms you'll need to correct for temperature and hiring a surveyor is probably the easiest option.
    Especially so if the site isn't level or if the layout is for a prefab shed.


    ian

  17. #17
    joe greiner is offline Old Goat
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    I was going to just postscript a suggestion to measure at night to reduce temperature effects. But a further question arises: To paraphrase ian, how "perfect" does it have to be? Most structures should have some local adjustment built into the design. Large equipment such as newspaper printing presses, long-line machining centers and such come to mind. In such a case, a surveyor would be mandatory.

    In an earlier career in the precast architectural concrete game, we always allowed a minimum of 25mm clearance to anything we didn't control, such as the building frame, and made up the gaps in the connection design. Then for the odd-ball cases, we made the specials to fit after the main parts had been erected.

    Joe
    Of course truth is stranger than fiction.
    Fiction has to make sense. - Mark Twain

  18. #18
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    Like TeeJay says, it depends what degree of accuracy you're after. I've only ever used profiles, stringlines and tapes. Unless your building something like a hospital or a shopping centre you don't need to get any more accurate than this will allow.

    Mick
    "If you need a machine today and don't buy it,

    tomorrow you will have paid for it and not have it."

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  19. #19
    cyberhonky is offline Apprentice (new member)
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    guys- further to what Ian said- the hypotenuse (A) is the square root of sum of X and Y squared (see sheet attached) just change the numbers for your dimensions.
    Attached Files Attached Files

  20. #20
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    Like Mick and Al says if it is for a prefab shed using the profiles is all that is necessary and set out the first corner with the 3, 4, 5 method and then just measure the diagonals using a steel tape.

    This was how we set out sheds and there is enough tolerance in them to allow for minor discrepancies and 30 x 40 metres is not that big really and if it was a shed being built on a slab the ground would have been leveled first.

    Our guys used to set out piers for sheds with the ground up to 1200mm out of level over 40 metres.
    Regards Bazza

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    The views expressed by the poster are general in nature and any advice should be taken in this vein. The poster accepts no responsibility if this advice is used. When undertaking any work personal professional advice should be sought from suitably qualified persons in the field of work being undertaken.


  21. #21
    Ivan in Oz's Avatar
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    Default Not Fair

    Quote Originally Posted by Chesand View Post
    5, 12, 13 also works. 5 & 12 are the sides, 13 the hypotenuse if it is sqaure
    Chesand,
    You took the easy one:mad:
    OK
    9, 40, and Hyp is 41

    Wanna be a mighty long piece of Timber
    Navvi

  22. #22
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    For those that have Microsoft Excel here is a Hypotenuse Calculator.
    Attached Files Attached Files
    Regards Bazza

    Skype Username: bazzabushy

    "Experience is a hard teacher because she gives the test first, the lesson afterwards."
    -Vernon Sanders Law

    The views expressed by the poster are general in nature and any advice should be taken in this vein. The poster accepts no responsibility if this advice is used. When undertaking any work personal professional advice should be sought from suitably qualified persons in the field of work being undertaken.


  23. #23
    Ekim is offline Novice
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    If you want to use the square root method (see Cyberhonky’s post above), then using the cell references in Bazza’a Excel model, the Excel formula for the Hypotenuse is:

    =SQRT((POWER(F15,2)+POWER(I11,2)))

  24. #24
    John99's Avatar
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    why not do it of a night and use the stars !:eek:
    Thinking about mowing the lawn doesn`t get it done !

  25. #25
    outback's Avatar
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    Quote Originally Posted by Vernonv View Post
    Other than for cropping (mainly), there aren't too many farmers around that have/use high accuracy positioning systems.

    I'm always amazed at the number of people (not just farmers) that expect their $200 GPS received to be accurate to the metre (or sub-metre).

    Even the 5 metre accuracy most receivers quote in nearly impossible to achieve under normal usage conditions.
    Ya gotta understand these farmers are after -2.5cm accuracy. Probably less than most shopping centres. Yes, for cropping only, but thats prestty impressive for 1000 acres. :eek:
    Boring signature time again!

  26. #26
    ian's Avatar
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    Quote Originally Posted by John99 View Post
    why not do it of a night and use the stars !:eek:
    I take it you have an atomic clock and a transit telescope

  27. #27
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    Talking Night

    Quote Originally Posted by John99 View Post
    why not do it of a night and use the stars !:eek:

    Why not do it at night and you will have difficulty in seeing any errors:eek:
    No Stars and
    you will have difficulty in seeing anything much at ALL
    Navvi

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