Map check closures

[Scott]

In the old days, before ACAD, we ran closures using the exact data we were going to publish as shown on our map (to the nearest 0.01' for distances and nearest 1" for bearings. Actually, I am still doing that, but I see others are not. I see closures that carry the distances run to the nearest 0.0001'. The map check closures are to verify the data shown on the map is a closed figure to some accuracy and that the individual closures will join together with thier common lines and make one big figure. I think if your closures are run from your calc sheet, using precisions greater than shown on your map, then you really are not checking the map data.
Opinions?
PS A previous post by Ian about closures is Titled "Closure Reports and sanity…………", if anybody cares to look at it.

[Jim Frame]

The only time I run closures with angle/distance precisions greater than published is when an obstinate map checker won't accept the closure otherwise. I agree that the purpose of closures is to verify the accuracy of the published data, and that the closure software should use rounded values in its calculations, not just round the output. I use custom software for the purpose; I don't know what the major software houses are doing these days.

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[Scott]

Thanks Jim, that is exactly what I am talking about. I am not just looking for the precision to be the same as the map, but the program has to run through using those exact distances (nearest 0.01') with no change after the hundreths place. LDD does that for me.
Anybody else?

[RAM]

We do not use our cad program to generate the closures. We use an indepent routine and hand enter the data to the 0.01' and the 1" to reflect our map as a true check, it also satisfies the County Surveyor.

[goodgps]

I agree heartily

The closure report should show the results of the published data, not some assumed out of this world exercize of computor mathematics.

But like Jim, I will "up the ante" in decimal places if some idiot map checking twerp thinks that will prove out the map.

The standard may stil be 1:10000 ? I dont know anymore ?
but who is surveying to the 4th or 5th decimal place anyway. All the more reason to have "True experience" prior to seating for the LS exam.

Fortunately in our immediate area, We have map checkers with common sense and extraordinary talent.

PELS,
I love the story of the old days closures. My dad had me write down the report while he worked the Olivetti.

good

[pls7809]

Technically, if you use LDD to run your closures, you click the lines or parcels you want closures for and then it spits out a calculation, error of closure, etc. LDD does this calc based on the unit precisions you have set up in AutoCAD. I figured this out because I couldn't get a closure of less than 0.02' (as required by most counties, rather than 1:10000 or whatever is acceptable) on my GPS control figure on sheet 1 of my RS. Long distances will do that to you. So I changed by precisions to 0.1" for my bearings and then re-ran the closure, without changing the lines at all, and now my closure was 0.005'.

If you are set up to 1" and 0.01', it calculates the closure at those settings, not to the infinte decimal place.

Then after getting the report, I hand check every dimension on the map.

[RAM]

To me clicking on the lines of your map is not an indepent check. That is why we close the map file and hand entry the data for a true indepent check.

[pls7809]

Which is why I check every demension on the map by hand after the map check is complete.

[Peter Ehlert]

Thanks for the tip Martin... in this day and age of simple computing there is no reason to have those simple math errors on a map.

we chase enough error on the ground without having to find the blows on the map too!

[goodgps]

The so called "map closures" used to be for finding gross errors such as incorrect bearing quadrants or transposed distances etc. The units were run out "as-shown" just to prove that the math really does close within a 1:10000 ratio error.

Today, closure reports (no matter how generated) are used by map checkers to hold maps hostage.

Truely, all closure reports should be office checked to catch little erors such as bad o-snaps or non-trimmed lines etc. These initial reports should be used by the drafter, even before the "fluff" of the map is created. or in otherwords . . . during base calc sheet prep.

The rub, sometimes happens, when we add a reference monument to show location, and label the distance as (reference only) . soon some linework gets closed on the (reference) loops and voila the checker wants a closure to prove this portion of the map that wasn't even surveyed. Sure the point was used for line only maybe from two different direction but now it becomes a mathematical burdon to the process.

On the otherhand, NO, just running an inverse closure around the figure does not satisfy and "error representative" closure.

Public agencies asking for closures on every 60x100 lot is overkill. But that sort of thing is being written into policy for cities all around California.

PS, checking fees must go up in order to review all this data . . . right ?

"good"