topic Re: Rounding Errors!!! in Civil 3D Forum

Rounding Errors!!!

jensdragonfly — Tue, 03 May 2016 22:34:52 GMT

There is an issue when rounding in Autodesk. I think that typical standards state that when you 5 and over you round up and 5 and under you round down. This is the not the case in Civil3D. The attached image shows that 40.77 Plus 4.02 equals 44.78. If I was to ask anyone to add those up, you would nit get 44.78, but 44.79.

Apparently a long time ago some one thought it was thet other way around.

Re: Rounding Errors!!!

troma — Wed, 04 May 2016 13:35:48 GMT

Let's just try an example:

40.76724 ≈ 40.77

+4.01737 ≈ +4.02

44.78461 ≈ 44.78

Looks perfectly legitamate to me.

Re: Rounding Errors!!! - Status changed to: Solution Provided

peterfunkautodesk — Wed, 04 May 2016 13:45:42 GMT

troma's response is a great illustration of what is going on. The distance is rounded based on the length of the line and not based on the sum of two rounded station values. Excel works exactly the same way.

Regards,

Peter Funk
Sr Product Manager
Civil 3D
Autodesk, Inc.

Re: Rounding Errors!!!

troma — Wed, 04 May 2016 13:44:05 GMT

For further reading:

https://forums.autodesk.com/t5/autocad-civil-3d-general/rounding-of-values/m-p/4794571#M240764

Re: Rounding Errors!!!

doni49 — Mon, 16 May 2016 15:00:25 GMT

This is why I keep my WORKING files set to show lengths & stations to a precision of 4 decimal places -- it makes it easy to see things like this. The files that I actually plot from are set to more appropriate precision values.

Re: Rounding Errors!!!

doni49 — Mon, 16 May 2016 15:04:37 GMT

P.S. I don't know how many times I've had a corridor "drop to zero" because it extended past the profile. The corridor might have ended at 102+00.00 and the profile might have too so I was confused.

But when I changed the precision, I saw that the profile actually ended at 101+99.9985. My corridor ended 0.0015 ft beyond the profile. But because the profile was rounded to two decimal places, I thought it went to 102+00.00

Re: Rounding Errors!!!

codee — Fri, 24 Jul 2020 21:34:12 GMT

2020 and the rounding errors still persist. No adding... just labeling the surface at my survey point wrong. point is 100.005 and C3D labels it as 100.00

Garbage

Re: Rounding Errors!!!

ChrisRS — Mon, 27 Jul 2020 04:14:49 GMT

Garbage? ... Maybe ... Maybe Not. Let's look.

@codee wrote:
... just labeling the surface at my survey point wrong. point is 100.005 and C3D labels it as 100.00

Garbage

There are potentially two things going on:

AutoCAD and Civil 3D use the round 5 to Even rule. Typically "round number ending in 5 up" is taught in elementary school. In science (high school and up), accounting, and AutoCAD a less biased method is used. When the least significant digit is exactly 5, round to the neared even number.
- 100.005 rounds to 100.00 (0 is even)
- 100.015 rounds to 100.02 (2 is even)
- 100.025 rounds to 100.02 (2 is even)
- 100.035 rounds to 100.04 (4 is even)
  etc.
Civil 3D labels (and AutoCAD) round based on the full stored precision of the object being labeled, not the displayed value.
- 100.00450001 through 100.00549999 will display as 100.005 and round to 100.00
- 100.01450001 through 100.01549999 will display as 100.015 and round to 100.02
- 100.02450001 through 100.02549999 will display as 100.025 and round to 100.02
- 100.03450001 through 100.03549999 will display as 100.035 and round to 100.04

____________________________________________________________________________

What is the actual elevation of your survey point?

This is from a survey I received for a surveyor. (I converted LDT points to C3D Cogo points)

A Line has been created, snapping one end to one particular point.

The elevation of that particular point is 1654.780 (See lower right)

The elevation display precision is controlled by the
Drawing Settings Elevation Precision setting, in this case: 3. (see lower left)

The elevation of line endpoint is 1654.77990000. Display of this elevation is controlled by "Units"

Rounding is based on the full precision of the point elevation, or surface elevation.

Re: Rounding Errors!!!

jmayo-EE — Mon, 27 Jul 2020 21:15:50 GMT

Civil 3D rounds with the half-to-even rule.

https://forums.autodesk.com/t5/civil-3d-forum/round-normal/m-p/2644574#M126748

https://en.wikipedia.org/wiki/Rounding