Parallel lines not actually parallel

[Doug]

I had the same problem. "My computer" did an update to Windows 10, and everything seemed fine until I started a new project. I layout a project using offsets. Then I tried to dimension the grid and they were off "just a little". I am sure the steel company would have loved to use that grid for shop drawings! I did the usual circle Revit, Dell, Windows, me... finally I took the computer to MICROSOFT STORE, the did a restore and everything is just fine in my world! Do you have WNIDOWS 10?

[Duncan Lithgow]

No Windows 10 here. Happily being productive with Windows 7 Professional. They'll have to drag me screaming "Right to privacy!" before they switch me to Windows 10.

How to reclaim your privacy in Windows 10, piece by piece

[CAtDiva]

No Windows 10 here. Happily being productive with Windows 7 Professional. They'll have to drag me screaming "Right to privacy!" before they switch me to Windows 10.

How to reclaim your privacy in Windows 10, piece by piece

Thanks for that link ... I'll definitely be using it when I upgrade.

[ken.peters]

I do not believe it is Revit. The lines may indeed be parallel. The big brains at our office say it is the way computers calculate floating point decimals.
and you are asking for measurement accuracy beyond the limit of the programming.

Nice video it is interesting to see it in action.

[andrewharle]

I have had issues when tracing a DWG, due to inaccuracies in the DWG. Quite often people draw in a user coordinate system in AutoCAD which looks fine in AutoCAD but when brought into Revit lines will be a fraction of a degree out of true, and lengths will be fractions of a millimetre out. Revit's import/link function has an option which is ticked by default to correct lines that are slightly off axis, but I'm not sure this actually works.

I tried modelling over a DWG of a piece of furniture once and had to give up and start again because the DWG was not accurate enough for Revit, so mirroring and offset caused problems.

[peterdew]

I'm also shocked that it shows such small distances. I would never have noticed it except that I have a QA dimension type I was using as I worked on a non-orthogonal wing of the project. It measures in mm to two decimal places. I've only stressed about it as I was concerned that the incremental inaccuracies would snowball into a larger problem. Clearly I can't get away from this issue so I'll just have to live with it.

Nice that you also think it's just internal Cartesian X,Y inaccuracies.

Thanks for your help good people.

Perhaps you are right to draw attention to it, but measuring to 2 decimal points using mm ?
Do you really mean you are modelling and dimensioning things such as 300,201.01mm
ie 300 metres, 20cm and 0.01mm ?
Can't you simply switch dimension mm to 2 decimal points off ?

[Duncan Lithgow]

... it is the way computers calculate floating point decimals.
and you are asking for measurement accuracy beyond the limit of the programming.

I'd love to understand decimal floating points better than my small brain can... As I understand it the reason for using this approaching is precisely because it allows the huge range of values CAD software needs (even more what CAM and GIS software needs).

Yeah, the video is really something. It somehow seems counterintuitive to me after years of interaction with CAD software to realize that of course it's not infinitely accurate.

- - - Updated - - -

Can't you simply switch dimension mm to 2 decimal points off ?

Yes I can. As I wrote earlier, I have a dimension style colored red and showing two decimal places for quality control purposes. Nasty things can happen when users drag objects around.

[DaveP]

This is a gross oversimplification, but think of it this way:
Let's say your small brain can only remember 9 digits:
123456789
But it can also keep track of the decimal point.
Now, that decimal point could be anywhere within that string. However, you can still only remember 9 digits.
So you can remember
1.23456789
or you can remember
12345.6789
or you can remember
123456789.
but you can never remember more than those 9 digits.
So, the more digits there are to the left of the decimal, the less your can remember on the right.
That means you lose accuracy the larger the number gets.

Now, obviously, your computer can remember a lot more than 10 digits, but it's the same concept.
If you model your building 200 miles away from the origin, it's going to have a hard time being accurate to 0.0000001",
but if it's close to the origin, it's got more room for more decimal places.