CAD question, re closure calculation errors...

[Lee Hixson]

I (and virtually every other Autocad/Autodesk user I know) have always had trouble running closure calculations. Inevitably, there will be some of your figures that "error out" when you try to create a "Parcel" in order to run a closure calculation. A white "X" appears the the junction of two lines (or a line and a curve) and it asks you if you want to "force a closure."

Most of my fellow CAD friends say to just use grips to make sure you snap one line to the end of the other one. This usually works. But sometimes it doesn't work. In either case, it makes it harder, and takes longer, to run your closures when you have to stop and fiddle with the line work all the time.

And yes, I've tried it both ways: defining the figure as a polyline, and defining it as a series of lines and curves. I've got a line with 7 segements today that simply will not close at this one point.

Has anyone figured out a sure-fire fix for this irritating problem?

[Lee Hixson]

Thanks, P.A., I'll use that next time I'm running closures on closed figures. That will probably take care of it.

Trouble is, today I'm trying to generate a closure using the inverse routine on an open figure: a design centerline for a new section of freeway that is composed of a series of tangents and curves. On some of the other design lines in my drawing I have successfully run such an inverse closer, but this one design line keeps slapping an "X" at this one juncture of a line and a curve.

Any ideas on fixing such an open figure?

Thanks, Lee

[dmi]

You are correct. It is a pain. I do not think there is a quick fix. When the figure does not close, then you has to stop and fix it somehow. The trick I use to is fillet with a zero radius and that fixes the problem. If it is a tangent curve, then I fillet the back and forward tangents with the radius I want. I always check after the fillet operation to make sure that the entities still report the values I want. I have used Bpoly, but you have to be careful because bpoly will find a way to create a closed figure even if it is not the one you want.

[Scott Tikalsky]

Lee:

1st, how are you? I haven't talked to you in quite a while.

I think Marc has your solution. This has always been a problem. Whenever using grips to connect endpoints doesn't work, I have fund elevation issues to be the fault.

Say hi to Dan & Rich for me.

[Ian Wilson]

Man, am I glad that others are facing this problem, too. I was afraid I was the only one. At least that's the tone I get fro the agencies.

Of course, part of the problem here is that the agencies require a numerical closure to a specific value regardless of the size of the project. +/- 0.02' for a 25x80 city lot or an entire section. It doesn't matter that the precision is 1:10,000 or 1:1,000,000, they "need" that +/- 0.02 to check that lil' box!

[Lee Hixson]

Dane...

I tried your idea and it worked. I erased the curves, then re-formed them using the fillet command and it allowed me (oh thanks, AutoDesk peeps) to run my closure.

So this makes me wonder? Over the last 10 years, how many hours (yeah, even years worth of hours) have been wasted by sundry cad people jumping through extra hoops in an effort to "work around" this problem? I wish I could have all my own wasted hours back.

This simply HAS to have a fix. For example, why couldn't there be a "gap closure" setting within the Parcel menus, such that you could dial in the gap that's allowed when running a closure? For example, if you set it to 0.00001 then any drawing gaps less than that distance would be ignored.

Scott.....

Thanks for inquiring. Yes, we're all doing fine. I'll say hi to everyone.

[pls7809]

I am totally frustrated by this as well. I am admittedly more a Microstation user than AutoCAD user, but I prefer typing in the bearings and distances into a third party closure program instead of using the one that comes with AutoCAD. It usually only takes a one time typing it in and then one time combing through the parcels that didn't close to 0.02'.

Ian...I have the same gripe as well. What do you do when you have a closure around a section of freeway maybe a mile long and there's a 28,000 meter radius curve along the frontage road? If your delta is 0°01'50" on paper (actually 0°01'49.55"), your length will be off by a huge amount and your parcel will not close within 0.02'. I'm dealing with this right now.

[Stan_K]

Ryan - Begin your Parcel Closure calculations immediately AFTER the small curve. You may need to redraw you polyline if using that method. This will limit the effect of small curve inaccuracies to the last course. This also applies to very long radius curves.

Stan

[pls7809]

There's a county where the checklist they send back says "closure within 0.02' (8766)", but when I read 8766 it doesn't mention 0.02' anywhere. It does talk about mathematical accuracy, but is 0.02' just picked out of the air?

[Dave Karoly, PLS]

Years ago I asked my boss about a silly agency requirement like that. I don't remember what it was.

He said, "Dave, you gotta understand they dream up most of this stuff over drinks after work."

Mr. 0.02' in his Martini has probably never actually worked on a field crew.

-PLS7849

[Ian Wilson]

Greg: the 0.02' is an arbitrary fixed standard. It's easier to have a fixed standard than having to calculate a ratio.

Ryan: we do what we have to so that we meet such a standard...we prevaricate (so much more polite than comit perjury or, for the agency, suborning perjury).

What about the two halves of a lie, each of which measures 100.145'? Each section is rounded to 100.14' but the total is rounded to 100.19'. That creates a 0.01' error in the cumulative total. Result: does not compute...error...error...must reject map...


Sometimes I feel like Tooter Turtle in the old cartoon...."Mr. Wizard! Mr. Wizard!"

"Drizzle, Drazzle, Druzzle, Drome, time for this one to come home!"...er...get back to work...

[PLS7393]

Man, am I glad that others are facing this problem, too. I was afraid I was the only one. At least that's the tone I get fro the agencies.

Of course, part of the problem here is that the agencies require a numerical closure to a specific value regardless of the size of the project. +/- 0.02' for a 25x80 city lot or an entire section. It doesn't matter that the precision is 1:10,000 or 1:1,000,000, they "need" that +/- 0.02 to check that lil' box!

Thanks Ian, I knew I was suppose to do something with that box!
Now where's my red pen?