CM instead of INCHES

[joe-2020]

what can I do if I want to work with cm instead of inches and if I have a building in inches, can I turn it to centimeters?

[barthbradley]

sure. Revit draws 1:1. Unit of measurement doesn't factor. 

[Anonymous]

Change the project units to centimetres.

[Anonymous]

From what I understand, Revit doesn't draw 1: 1.  AutoCAD does though.  Revit uses real world measurements that relate to the earths surface, so an inch is a specific amount of millimetres.  Revit uses inches internally and converts these to metric on the user interface.

[barthbradley]

Huh?  Sorry @Anonymous , maybe I'm misreading you, but I can't agree with this statement. Can you elaborate on your thinking?

[Anonymous]

Hi Barth - yes.

Consider how Revit places a project in real space.  Although AutoCAD has a coordinate system, it is not related to real space and you can have a coordinate system that covers a very large area.  That is a reason that Revit cannot deal with projects far from the origin, or projects that are too large to fit within the 20 mile radius.  The curvature of the earth becomes an issue for calculating distances and starts to throw Revit out.  For metric users, the fact that Revit calculates in imperial units can start to cause issues down the line, where slight discrepancies in the conversion calculations can start to cause lines to not be parallel or at right angles to each other.  This becomes noticeable when the accuracy of the units is set very high (12 decimal places).  It can lead to 'lines slightly off axis' eventually, but it is usually below the threshold for that.

[aRcHiTeCt.JM]

... hi @joe-2020 

... yes ...you can go back and forth between inch and cm

... as much as you need / want

... just change the project units

… hi @Anonymous 

… everything that you draw on REVIT is real size

… meaning 1:1 scale

… (either inch or cm)

… meaning … that all the dimensions are real - life sizes

… the model is 1:1 ……  but views are scaled

... that is the only way to put everything on paper

… @Anonymous  you are saying that it is not 1:1 because in a 20 mile radius distance (or more) the earths curvature will affect the scale by 0.000000000001 cms ?

… wtf !

… even if that were true

… I believe nobody is drawing anything bigger or larger than a few 200 – 300 meters?

… lets ask to @loboarch , @Viveka_CD  … @ everyone ...

… 1:1 is the rule … and that’s it

... as @barthbradley said I can't agree with you on this one ...

[Anonymous]

Perhaps my post was misleading – yes we do draw 1:1 but the units are not irrelevant.

What I mean is that Revit is not unit agnostic like AutoCAD.  In CAD, a unit is a unit – it doesn’t care. However, in Revit the units relate to actual distance. 

I’m not suggesting that 0.00000001cm makes any difference to anyone – not even Revit notices this, but it is the reason that Revit can’t handle such large projects from my understanding.

[barthbradley]

Your are confusing RATIO with SCALE.  1:1 RATIO.  

[loboarch]

---

@Anonymous wrote:

Perhaps my post was misleading – yes we do draw 1:1 but the units are not irrelevant.

What I mean is that Revit is not unit agnostic like AutoCAD.  In CAD, a unit is a unit – it doesn’t care. However, in Revit the units relate to actual distance. 

I’m not suggesting that 0.00000001cm makes any difference to anyone – not even Revit notices this, but it is the reason that Revit can’t handle such large projects from my understanding.

---

This is "kind of" true. In Revit, 1 "unit" internally is static. It is set in a way that assumes you are drawing "building sized" stuff. You can set the user interface to report units in inches, feet, CM, MM, etc... but internally there is 1 unit that is converted from and to based on what units the user has set.

Now separate from Revit, this concept of setting the "unit" is somewhat a declaration of how accurate you are going to be. Why this is important is because you can't be accurate at all "scales" in ANY software. Take AutoCAD for an example, there 1 unit is undefined at the system level. The user controls the "unit". You could specify angstroms (atomic level) or light years (galaxy level). once you set this however, you are defining what "zone" you are going to be accurate in. If you are drawing things that are a couple of angstroms across you will not be able to draw a line 1 light year long and vice versa. You are only going to be accurate and able to draw things in the general "range" you are working in.

Now back to Revit. In Revit the "unit" is set at the system level. I believe the internal "unit" is inches. So this sets the accuracy level of drawing elements. You end up be prevented from drawing things smaller than 1/256th inch and not greater than 20 miles. Drawing things greater than 20 miles also introduces problems with the earth's curvature as well.  

[barthbradley]

@loboarch: hear that?

My brain just exploded.

"Clean-up on Isle 5!!!"

Now try this question: At 10:00 AM Imperial Train left the station and an hour later Metric Train left the same station on a parallel track. If Imperial Train traveled at a constant speed of 60 miles per hour and Metric Train at 80 kilometers per hour, then at what time did Metric Train pass Imperial Train?”

Just being silly.  Thanks.  Good post.  

[aRcHiTeCt.JM]

... and this guy @joe-2020 was just asking if he can exchange units ... 

[barthbradley]

@Anonymous: I get your thinking. It's valid. 

@joe-2020: Change Project Units and "Trust but Verify".  It's going to be uncomfortable though. You're going to be dealing with "non-standard" measurements.  

[Anonymous]

It didn't - it's travelling slower.