This is a follow up to the [msg=150274]post on Friday[/msg]where the clerk wanted me to get the planning department to sign off on something over which they had zero authority.
Got a call this afternoon from someone at the Tax Mapping office. He wondered if I had screwed up the acreage on the map. My map shows 104.51 acres. His calculations showed 105.41 acres. To his credit he had made sure he had good closure. His closing error was 0.03 feet on a boundary with a perimeter of something over 13,000 feet.
I told him I would check my records and get back to him asap.
I used the Carlson/CG Mapcheck function and my point group created for that boundary. My closure error was exactly the same as his. The perimeter distance was also exactly the same. My acreage was 104.51. Hummmm.
Called the guy and told him I couldn't tell him what was wrong with his numbers but mine had been double, triple and quadruple checked. No polylines were used in my calculations so it couldn't be a case of CAD monkey (me) clicking and dragging the wrong thing.
I sent him a copy of my report and asked that he please check my figures against his figures to see if we could figure out what was going on. I was using the Beta version of Carlson 2013 so I knew is was possible (highly unlikely but possible) there was a math problem somewhere along the way.
He called me back a bit later having found the problem. He had the exact same bearings and distances as I. But he had "flopped" the order on two of the calls.
We both thought it really odd that transposing the bearings and distances would not mess up the closure. Gotta think about this a bit more. It might be that way on all closed figures. Meanwhile, anyone out there care to expound on your experience with this sort of thing?
Let me be really clear on what I am talking about here.
Course 1
Course 2
Course 3
Course 4 etc. was what was correct.
What he had in his system was
Course 1
Course 3
Course 2
Course 4 etc.
Larry P
It doesn't matter what order you add vectors, the sum is the same.
Without meaning to sound sarcastic or too flip, of course you will get the same closure. Think in terms of latitudes and departures. They are the same, just in a different order. So the columns add up the same, but when you do your DMD's or cross multiply coordinates the areas come up different.
Up Right Down Left = Up Right Left Down
Understanding this concept is likely the key to why I am a bad dancer.
I think I might know what they are talking about up there but not sure.
But YOU
“Up Right Down Left = Up Right Left Down”
Now you’ve done it, (again) I’ll be tryin to figger this one out for the next decade or two.
I understand the first part but as for the second, how do you up the right when you have to leave it down?
This is worser than one of them damn math word problems about trains leaving New York and Nome at the same time blah, blah, etc……..
Have a great 4th! B-)
What is more interesting is ....
the coincidence of the change in area transposing 2 digits. If the difference had been anything but that I suspect he would have looked closer and found his problem and you wouldn't have scratched your head so hard. Don't you just hate it when things like that happen?!
I can see the lat-dep getting you back to the POB, but the acreage? That part eludes me. It must be a coincidence.
:-S
you are a very nice guy... and the tax man in your area is trying to hard.
The tax man calling me to tell me my acreage is wrong on my survey would go over smooth once, and that is it.
> The tax man calling me to tell me my acreage is wrong on my survey would go over smooth once, and that is it.
The tax man would then probably chalk it up as yet another cranky surveyor who can't do math, use his figure, and your client will pay tax on an extra 9/10 acre forevermore.
> you are a very nice guy... and the tax man in your area is trying to hard.
>
> The tax man calling me to tell me my acreage is wrong on my survey would go over smooth once, and that is it.
He apologized for bothering me with the call. I told him to not hesitate to call me any time he say my work and thought there might be a problem. The important thing is to get things right.
I encourage anyone that sees my work to call if they have a question or problem. In more than 20 years now I have had a several calls. A couple of times they were right and there was a problem with my work. I figured once or so a decade is not great but acceptable.
Larry P
