Not sure what the problem is with over precision of units? ... You just round it off...
When one of us does something stupid it reflects on all of us who self identify as surveyors.?ÿ We all have a responsibility to each other to enhance the reputation of the profession.?ÿ?ÿ
ORS 92.050 dictates what must go on a plat. It specifies (read literally) that curve element lengths must be specified to the hundreth. It leaves all other precision stating requirement to the discretion of the County Surveyor. So if you are being required to show areas to the thousandth of an acre that is on the County Surveyor. 0.001 acre is 44 square feet, so it is a realistic expectation.?ÿ ?ÿ0.001 sq. feet, would be not so much.
Also leads to questions of why your work doesn't match the other survey when you report 13.25 acres and they reported 13.24982 acres. Not everyone was clear on rounding numbers in math class and they don't want to pay for that extra .01 acres.
Also leads to questions of why your work doesn't match the other survey when you report 13.25 acres and they reported 13.24982 acres.?ÿ Not everyone was clear on rounding numbers in math class and they don't want to pay for that extra .01 acres.
I once prepared a survey of a large prime development tract ($) with the knowledge the determined area I reported was to be used to calculate the sale price.?ÿ My attorney got with all the parties and it was decided and agreed upon that my reported area would reflect the nearest square foot?ÿ?ÿ(six decimal places if I remember correctly).
As a matter of ALTA standards I reported measured and record distances?ÿon the survey and the area was determined using measured distances.?ÿ Thankfully there were only a few hundredths scattered about the +/- 80 acres tract.?ÿ But the buyers legal team became stuck on fact that my measurements were subject to the minutia of mathematical closure.?ÿ They argued for a month over less than 100 odd square feet.?ÿ ?ÿThey finally decided upon a final price.?ÿ
It dragged on and I didn't think I would ever get paid.
Client: I need the area to the nearest 1/100th of a square foot.
Me: I'M A SURVEYOR, NOT A MIRACLE WORKER!
You do realize that we can't, or don't, measure accurately enough to calculate areas like that, right?
The "science" of surveying involves acknowledgement of significant digits.?ÿ
A few points on that:
- Using significant digits may not increase your precision, but it will improve the accuracy of your statements. (If you can reproduce a measurement of 1 foot 100% of the time, then stating "1 foot" is more accurate than stating "1.0001 foot" when your measurements vary by 0.1' every time. It is about the accuracy of your statements.
- Measurements are subject to significant digits.
- Calculations (still subject to significant digits) can typically be of greater precision than your ability to measure. In the time of slide rules, then the precision of your measurement tools informed how precise you cared to make your calculations. So simply saying that you cannot measure better than 0.01' does not mean that some calculations could not reflect a better precision without violating the principles.?ÿ
?ÿ ?ÿWe spent about a week in High School learning about and practicing significant digits during my Chemistry class. I think that would be a great refresher course for a surveyor's conference.?ÿ
In practice we see how well measurements can be reproduced on the ground every day when we do our field work.
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For instance, if I hit a corner by another surveyor within a tenth of a foot I am generally pretty satisfied. I wouldn't generally even consider that tenth as missing the corner. So let's apply that to a 100'x100' box (10,000 sqft)...?ÿ
If I am off by a tenth all the way around in the wrong direction I could have between 9960 and 10040 sqft inside of the corners. So, I would submit that most of us violate significant digits almost every single day.?ÿ?ÿ
Client: I need the area to the nearest 1/100th of a square foot.
Me: I'm a surveyor, not a metrologist. To determine that kind of precision I'm going to have to monument the property with etched brass disks in concrete pillars set well below the frost line. We are going to have to bring in a team of metrologists to make the measurements with equipment far in excess of normal survey equipment. They can only do this work at night, unless we build a geodesic dome over the entire property. It's going to cost a hundred thousand dollars to do your acre.
Go for the wallet. It has a marvelous way of stimulating the brain.
Not sure what the problem is with over precision of units? So what if he computed out to 10 decimal places? You just round it off to whatever decimal places your instrument is capable of laying out right? Problem solved, you get paid, on to the next client/
Well, the person drafting the plat is probably working off a boundary/topo survey performed with equipment of lesser precision than what he's calculating for his lot dimensions, so right off the bat he's introducing error.?ÿ If you ignore it you either look equally ignorant or careless.
Client: I need the area to the nearest 1/100th of a square foot.
Me: ...?ÿ It's going to cost a hundred thousand dollars to do your acre.?ÿ
I think you severely underbid that.?ÿ For a square plot of one acre, you would need to know the sides within better than 3/10,000 inch or 7 microns, about a tenth of a human hair or 10 wavelengths of red light. Getting 10(-7) relative accuracy can be done but not easily over that length.?ÿ Etched disks would have to have the lines done at semiconductor chip precision. You might have to build a 209-ft interferometer, stabilize it mechanically and for temperature , and count fringes.
I assume the attorneys made more than the value of the $100 square feet!
As a matter of practicality areas are fixed for a lot, 1/4, ect. They can be fixed by patent, recording, acceptance, but the point is a Lot in a subdivision meeting the 6000 sq. ft. minimum for R-1 zoning is legally a 6000 sq. ft. lot even though measurements may show it to be 5992 sq. ft. The law doesn't like changes to people's rights and protections.
Two patented 40 acre 1/41/4 can be sold together and meet the Ag zoning for an 80 Acre minimum sale of land. Even if they measure less. The patent established the legal acreage and it remains until the 40s are split.?ÿ
The idea that a Lot in a Subdivision is platted as 6001.25 sq ft is an example of not knowing what the heck you are doing out there.?ÿ
@mightymoe Speaking of DOTs / Highway Departments: Seen in Lancaster, MA. This sign has been there for years now.
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Are we measuring this on the plane or on the spheroid? (Depending how many acres, it might make a difference).
Are we measuring this on the plane or on the spheroid?
Mark-to-mark on marks set at the same orthometric height. If someone wants a different representation, that's their problem. 😆 ?ÿ
Or when a tract is hundreds of acres and labeled to a thousandth of an acre
Or when someone is referencing a monument a foot away to the nearest second and hundredth?ÿ
Perhaps. The number on the sign is exact for international feet and is the same as the one for US survey feet, rounded to 4 decimal places.
Maybe it really is US survey feet,but there just wasn't room on the sign for all of the digits. Here it is to 50 decimal places: 3.35280670561341122682245364490728981457962915925831
Some folks might need more, though. You just never know.
I was a stickler concerning sig figs for decades and grudgingly endured?ÿ unreasonable requirements by third parties (gubmnt' agencies, attornies, etc.) as posted above.?ÿ I finally woke up and realized it's a picayune matter; you demand square footage to 2 decimal places, or the bearing of a 2 foot line be to the nearest second, sure, here it is.?ÿ The aggravation of standing your ground just isn't worth it, and the liability is practically nil.
