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Rounding Error
Posted by RADAR on October 27, 2021 at 9:10 pmI’m working on a plat and want to divide a 653.40′ line in to 7 equal distances. When I use the handy “Divide Along Entity” command I come up with 93.34′. When multiplied by 7 equals 653.38′.
Would you:
- Change 658.40′ to 658.38′
- Make 2 of the lots 93.35′
- Leave it, and wait for someone to tell you, you did it wrong
Thanks in advance, to all of the good people on this board, that respond.
You guys are the best!
Dougie
dmyhill replied 2 years, 5 months ago 21 Members · 56 Replies- 56 Replies
Option 2
If somebody is going to call you on 0.02′ over that distance, let them, then, to fire back at them, revise your plan to show distances in six or eight decimal places.
93.34286063058036 feet per lot, although 93.343 would probably just as silly.
That should keep the GIS department happy.
Seriously though, I agree with Chris.
????
Since I live and work in Oregon, Option 2. But don’t just explode the annotation and edit the resultant MTEXT. Actually recalc the points and move the line endpoints. If you don’t your area calc will fail.
If I was still in Oklahoma, Option 3.
Option 4
Show each length, and the overall length. Whenever someone asks, use the opportunity to explain significant digits, and then apologize for showing it to the hundredth and not a tenth, which would be closer to reality. Then, do whatever it takes to get the reviewer to sign off.
-All thoughts my own, except my typos and when I am wrong.2+2=5 for very large values of 2.
Many years ago when calcs were printed on dot matrix printers and the lot fronts didn’t add up to the total along a long tangent on the RW, a mentor literally would create a fake inverse to print out, then use an Xacto knife to cut out the “fake” distance, tape it over the one in the calc sheets that needed 0.01′ added or removed to match the tangent total (make sum of the parts add up) then make copies to submit for checking. He was also the King of Practical Jokes, so it was sort of a game to him.
Significant digits schmignificant digits.
I used to do Option 2 but lately I just put the rounded number on the Map, they don’t add up exactly but that’s reality.
I do a map check calculation, on every closed figure which I enter into my Excel map closure checker. But I hate automatic text things. I type in the B&D for everything. Maybe if I worked for huge firm incorporated I would use automatic text on surveys with a lot of lines but most of ours are not too bad.
I was looking at a Traverse in 1934 GLO notes, bearings to nearest minute, distances to nearest link. If I compute it in a cogo program the answer is different than their answer, so I computed it using latitudes and departures to the nearest link and voila I get their answer. I’m sure sitting in a tent computing at night after a hard day crossing uncrossable canyons they didn’t care too much about exact precision.
Option 2 unfortunately. The plancheckers insist it all add up due to a tick mark on their review list. Any discussion of sig figs is wasted breath. It’s tedious manual work as no computer can “fudge” coordinates. Worse is curves which require 3 parameters according to their “punchlist” which often doesn’t add up perfectly with tangent PCs & ECs, much more hassle if sublengths are involved.
When I was “Mr. Big” in subdivision mapping involving 50+ lots I’d get the design from the grading/planners and spend a few weeks lotting, making sidelines being right angles or radial, avoidance of interior corners only being a few tenths apart, etc., make sure all lots met minimum acreage requirements, utility easements properly delineated, etc. To do so sometimes the optimistic planners lot count had to be cut back by a lot or two to meet all the regs and I was the problem child as those last two lots are pure profit. Once or twice I squeezed in an extra lot and was a hero.
The sad part is I’d finish with a crystalline accurate map but have to review the entire map and fudge sublengths, etc., to make B/D & curve values add up to the hundreth & second, which took another few days+ of headscratching. A total waste of time but all firms had to do it so it was merely an added cost for all. The losers are the public, higher prices for a lot because of silly hoop jumping at the Courthouse.
As a plat reviewer I would accept Option 4. But in other jurisdictions Option 2 might be the smoother path, and I would accept it also.
I have no problem showing a 999.98 foot line with ten lots as 100.00 each. There are ten equal distances, all of which round to 100.00 feet. Artificially changing the overall or making one lot a different distance obscures the intent for ten equal lots on the monumented line. There is no statutory authority in Idaho to make me draft it different.
Surveyors have no problem with understanding the rounding “error”. Trouble comes when folks like attorneys, paralegals, real estate agents, and the general public use our maps. The recording agency is going to be the first line of defense for answering the stupid questions that will inevitably arise. So they are, understandably, very picky about these things.
@thebionicman I just kicked your monument 2 hundredths so now your math works.
- Posted by: @dave-karoly
I hate automatic text things. I type in the B&D for everything.
Everybody stay off Dave’s lawn!
- Posted by: @mark-mayer
The recording agency is going to be the first line of defense for answering the stupid questions
For a long time, in Washington State, the Surveyors stamp had the expiration date on it. Your license needs to be renewed ever 2 years, on your birthday. So your stamp had your birthday, but the year was blank.
Enough people asked the stupid question: Is this when my survey expires? So they made us take it off. If you had a rubber stamp, you took an X-acto knife and scraped it off.
Digital was easier…
I hope everyone has a great day; I know I will! - Posted by: @dave-karoly
I type in the B&D for everything.
I used to type in everything; then my dad got a job
Why do you dislike line labels?
What’s wrong with typing in information? That’s the simplest way to make sure parallel lines are parallel and lines of identical lengths have identical numbers listed. Auto-anything is dumb. Such software does not understand “what I really meant was…….”
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