Unit system in AutoCAD

[Kyudos]

Can someone explain to me why AutoCAD does not have a proper unit-of-measure system?

Is the unitless approach a legacy thing? Did it save CPU cycles somewhere back in the dark ages?

With the commputing power available today, I don't see any reason for AutoDesk to NOT have implemented something more logical.

AutoCAD is used to draw/design real-world things, why then can I not work in (real) real-world units?

Why can I not change display units and have AutoCAD scale my input?

(e.g., I tell AutoCAD I'm working in metres and draw a 10m line, then I tell AutoCAD I want to work in feet and draw a 10 ft line - I don't want them to be the same length, I want them to be relatively the correct absolute length).

I find the current set-up completly bizarre and wrong-headed - espeically in the era of the internet and international collaborative projects where different people use different units. Why not have your base (absolute) unit fixed as a property of your DWG? Or better yet, why doesn't (hasn't) AutoDesk picked a base absolute unit to use internally that can be interpreted through fixed conversions as any unit the user wishes to see?

[dgorsman]

Welcome aboard.

Piping and Instrument Diagrams (P&IDs), Mechanical Flow Diagrams (MFDs), and electrical schematics aren't real world objects.  AutoCAD continues to be the jack-of-all-trades tool, a Swiss Army knife of CAD, so lacking units isn't that big a deal.  FYI, the vertical versions along with Inventor and Revit which are more focused *do* implement a concept of units.

[Kyudos]

Ok granted, not everything done in AutoCAD is 'real-world', but not even an option to use proper units in the base offering? You have to rely on the vertical apps?

[3wood]

You can draw metric and imperial in separate drawings, and xref or insert one into another.

[Kyudos]

But that is my point - you can't "draw in metric or imperial" real units, you can only draw in unitless numbers that are accepted by convention to be some representation of a metric or imperial unit. I'm saying you should be able to work in absolute units if you want, and change between unit representations. That would mean if I'm working in metres and draw a 10m line, then switch my units to ft AutoCAD should tell me that my line is 32.8084ft long - and I'm not talking about drawn dimensions either - I want my line to have an absolute, real, length.

[JDMather]

-dwgunits and follow the command line.  (with the preceeding - sign)

Not quite the same as their modern products that allow any appropriate units at any time.

[scot-65]

This might help.

[Kyudos]

Hi JD - I'm aware of -DWGUNITS, but that just scales one set of unitless numbers to another set of unitless numbers, your 'things' still don't have any absolute size.

I'm just failing to see any advantage in sticking rigidly to the unitless paradigm.

[Kyudos]

Hi Scot - I'm not struggling with unit conversion, I'm wondering why AutoCAD doesn't have the option for me to work in real, absolute, units

[dgorsman]

There are higher development priorities.  Not to mention hundreds of thousands, if not millions, of legacy drawings that would need to be updated ie. is this drawing in meters or millimeters?

Ideal?  Probably not.  But what is, is.  Yes, I could fight for it but the likelyhood of change is small as is the annoyance.  Discretion being the better part of grey (or no!) hair, I choose to fight more appropriate battles.

[Kyudos]

Higher development priorities than making AutoCAD work in a logical and consistent fashion? 

I don't know why anyone drawing a real-world object would want their unit set open to any form of interpretation.

If this was an optional way to work, there would be no need to do anything with legacy drawings unless the user so wished.

I'm guessing AutoDesk has more than a few developers on staff, this wouldn't be a project of more than a few months surely? What bemuses me is why they haven't already done it!

(but I (and my hair!) agree - I can't see them changing)

[JDMather]

In  a modern next-generation program like Autodesk Inventor I can enter any units I need at any time.

The program retains the units designations.

I work in the mechanical design world.

What field do you work in?  Maybe Autodesk has already developed a next-generation tool for your field of work.

[JDMather]

---

@Kyudos wrote:

Hi JD - I'm aware of -DWGUNITS, but that just scales one set of unitless numbers to another set of unitless numbers, your 'things' still don't have any absolute size.

---

Uh!

When I set the units with -dwgunits and take the file into any other CAD program the "things" are the same absolute size.

What other software are you using that doesn't correctly read the AutoCAD dwg units.  (I can also export out from AutoCAD is several other formats - and the units are correct when opening in the other CAD programs I use.)

Have you confused the AutoCAD units command with the AutoCAD -dwgunits command?

[3wood]

I think -DWGUNITS works well except it takes a few steps to the final result.

[pendean]

It appears you are ready to move on from AutoCAD to more advanced CAD tools (from Autodesk or others): what's your industry or specialty? AutoCAD is obviously the wrong tool for you (and no one is going to change it just for you).

[JDMather]

I'm still waiting for the OP to post an example that AutoCAD is not "units aware".

I can post AutoCAD examples translated to other CAD programs that demonstrate that AutoCAD dwg does store units information (and writes units information to several neutral and proprietary formats besides dwg).

[Kyudos]

Hi JD - the image you showed for Inventor was the kind of thing I was expecting in the base AutoCAD. I didn't expect unit handling to be a special-case scenario for a CAD progam.

Yes AutoCAD has a unit setting, which it appears to use to scale things which are inserted in other drawings. This may be exported and interpreted by other CAD programs with 'proper' unit systems, but AutoCAD doesn't use them (as far as I can tell).

To repeat my example - in AutoCAD, if I set the units to metres and draw a line from (0, 0) to (0, 10) I get a line 10 'units' long. If I then change my units to feet, I would expect AutoCAD to show my line as being from (0,0) to (0, 32.8084), but my line is still from (0,0) to (0,10) because it doesn't really have any units. The INSUNITS are just 'what the designer thought he was using when he drew this', the numbers themselves are unitless.

I'm looking at some ARX development, and I can work with how the system is, its just not as straightforward as it could be.

[JDMather]

What does the command line say when you use the -dwgunits command with your example?

Also, you didn't answer the question about what field of work you are in.  There might already be an Autodesk 21st century tool that has the functionality you need.