AutoCAD units 1

[MarkWoodley]

I have been told that AutoCAD 2002 is a unitless system, that is to say one drawing unit could equal one inch, one millimeter, one mile, one lightyear, etc.....

Is this true?

If so, please explain.

If not, can you tell me how to locate what measurment system the drawing is in and how to alter my drawing units from Metric to Imerial and vice-versa?

Thanks
Mark Woodley

 

[jtt]

Hi Mark,

1)You can see the measurement system of a drawing and you can set the units from File menu - Units (or by typing "units" in the command line.
2)If you just want to change the units shown in dimensions,you can change it in Dimension Style.
3)If you want to convert from one measurement system to another, you'll need to rescale the drawing
For example,"to convert inches to centimeters, you scale the drawing by a factor of 2.54. To convert from centimeters to inches, the scale factor is 1/2.54 or about 0.3937" (AutoCad 2002 User Guide).

It will be easier to understand if you look up in the online help or in AutoCad 2002 User Guide.
You can download the AutoCad 2002 User Guide from <ftp://adeskftp.autodesk.com/WebPub/education/manuals/a2002ugd.zip> (it is a large file [41.9 mb]

Have a nice day,

John

 

[CarlB]

That's essentially true, AutoCAD is unitless, except when it comes to plotting scales and paper sizes.

To know what scale was used for creating the drawing, you can query an object of known dimensions, see what it reports, and figure out if it was drawn in feet, inches, mm, meters, etc.

Then if it's not at the scale you want, you can scale everything in the the drawing, using the scale factor to convert from one system of units to another. For example if it's in meters and you want it in feet, scale by 3.28084.

hope this helps,
Carl

 

[tigrek]

I find it best to leave the drawing content at real world sizes: 1 unit for 1 inch or foot or km or whatever.
Then, for plotting purposes, insert a frame drawn to size of paper but enlarge this block by intended scale on paper.

Scale in dimension texts is another matter.

 

[MarkWoodley]

I am still having problems with this entire concept of scaling to convert measurement systems.

If I draw a rectangle in AutoCAD 2002 of size 11&quot; by 7&quot; and then convert it into millimeters (according to the above) it must be scaled up by a factor of 25.4.

I now import my text blocks into the drawing and then when I export the drawing as an AutoCAD 12 *.dxf file, to import into an engraving program, the other program sees a rectangle (with text blocks) that is 279.4 INCHES (not millimeters) wide by 177.8 INCHES tall. But if I have converted my drawing to millimeters why does the engraving program still register the drawing size as inches?

I do not understand why you need to scale a drawing to convert it to another measurement system? The above scenario indicates that when you scale a drawing you are changing the SIZE of the drawing not the UNITS. Should a drawing not be the same size regardless of measurement system? If I continually re-scale my drawing then I will encounter rounding errors that will alter the dimensions of the drawing.

If I draw a line 1 inch long then I have already drawn a line that is 25.4 millimeters long. Once I scale the line up by a factor of 25.4 then I have a line 25.4 INCHES long (which is 645.16 millimeters long).

Please explain?

I am also having problems with the UNITS command; I cannot locate the global measurement change. The only indication of units is the &quot;Drawing Units for DesignCenter Blocks: When inserting blocks into this drawing, scale them to -> inches, millimeters, (etc....)&quot;
I am not using DesignCenter Blocks, I have created my own text blocks and I am inserting those. I also want to determine my measurement units prior to creating a new file.

 

[CarlB]

Mark,

You're trying to give AutoCAD too much credit for thinking - it doesn't know all the different possible units, it only knows how to draw something a given dimension you provide, it just keeps track of numbers. When you draw a 1 inch line (inches in your mind), it draws a line 1 unit long, AutoCAD doesn't know it's an inch (can't read your mind) and doesn't know it's the same as 25.4 mm or 0.083 feet or whatever. (May be an exception for dimensioning with alternate units, limited conversion capability). From your description, your engraving program interprets a length as being in inches, either you need to always provide it dimensions you want in inches unless you can set it to read other units.

Hope this helps,

Carl

 

[CDH]

If you are simply changing the units from Architectural to Decimal, then yes you will need to scale it (see below), because if you draw a rectangle 11&quot;x7&quot; and then change to decimal, you now have a rectangle that is 11.0x7.0 1-unit = 1-unit and you import into your program and is recognized as 11&quot;x7&quot;

Now, if you have ADT, you can go into the drawing setup and change the &quot;Drawing Units&quot; to inches, mm, cm, whatever, and it will automatically change the drawing to display the correct units without having to scale it.

Instead of scaling it up 25.4, I think you actually need to scale it by 0.03937 (1/25.4)
For example, if you want a rectangle 100mm x 100mm, draw it at 100x100 using decimal units, then scale it by 0.03937
and you have a rectangle that is 3.937 x 3.937 which you program should interpret as 3.937 inches.
If you scale it up, then you will have a rectangle 2540 inches square, which the prgram will also interpret as 2540 inches.
The way I understand it is your program interprets a unit in ACAD a an inch. Even if you draw that rectangle in decimal units, it gets interpreted as an inch. by scaling it down it is still interpreting an inch, but it is and actual inch this time.

Hopefully this makes sense and is what you are looking for and I hope I'm not confused in my thinking

chris

 

[jerryjumpjet]

What previous contributors have said is true about ACAD being unitless. It is unitless only up till you plot. That is where you apply scale. Now, all that is easy to say but not easy to implement. When you draw something at 1x1 unit that is what it is. (1x1 unit) This is the ideal situation. Always, I repeat ALWAYS draw at full scale. If it's 1 inch long or 1 mile it's 1 unit. You can &quot;truly&quot; draw anything, no matter what size. If you want inches; draw in inches. If you want millimeters; draw millimeters. Where it becomes more critical is when you affix a title block or text to your drawing. Before CAD, scaling questions needed to be considered because of paper size. You had to figure out at what scale would you need to fit on the paper (or material) you selected. Then react accordingly. Many times I've shaken my head watching a rookie operator going through all the trouble of scaling everything as if they were still drawing on a board. Now, with CAD you are not limited to a certain paper size. It's sort of backwards. Scaling only matters at output. (plot) Now, you need to figure at what scale you need to size your title block (paper) for what you are trying to represent. If you use no title block, it still applies if text is involved in either notes or dimensions. If you have no text or dimensions you still need to figure for what you want to spit out of you're printing device.
----ANYWAY, there used to be a setting when configuring your output device (printer) for ACAD that asked whether you wanted inches or millimeters. I'm not sure how that's set in the most recent versions. I would guess it's when you CONFIGURE YOUR OUTPUT DEVICE to work with AutoCAD. Most will probably default to inches with millimeters as a choice. Then, put in the scale. (plotted unit/drafting unit) [1/2 = half scale] -- [1/24 = (1/2&quot; = 1' scale)] -- [4/1 = 4x scale]

 

[AggieCE]

Mark,

I agree with what most everyone else has said, but have a couple of things to add. ACAD is unitless as described above. If you draw a line with a length of &quot;1&quot; it will be 1 unit long. The type of unit is set by you (the user) in your drawing setup, which affects plotting and measure-type commands. I agree with Jerry about always drawing at full scale (I think of it as &quot;real world&quot; scale). But it IS important to think about what scale you will plot at (i.e., 1&quot; = 100', etc.) before you begin drawing for at least one very good reason. If you will add text to your drawing, in the same file you are drawing your linework in, you will have to set up your text so that it will look right when you plot. For example, the standard text height at my company for general text is 0.1 inches when plotted. Let's say I'm drawing a plan view of my house, including my lot. Let's say my lot is 150'x300' (it is actually much, much smaller). Anyway, I want to plot it on a 24&quot;x36&quot; sheet, so after subtracting space for the border, I end up with about 33&quot; of useable width. So I've got to fit 300' within 33&quot; of paper. Thus, I need a scale of 1&quot; = 10'. In my drawing, I draw at real world scale (my units are set for feet), my linetype scale is set at 10 (for a scale of 1/10), and my general text height is set for 1&quot; height. Now, I insert some text in some leaders, dimensions strings, etc. Now when I PLOT, I plot the file at a scale of 1 to 10 and my plotted text height is 0.1 inches (also, my hidden and other non-continuous linetypes look right). Does that make since?

Okay, here's another thing. I see alot of people draw a scaled-up border, and that's fine. I prefer to draw my border in a seperate file in paper space at full scale, then draw my line work in model space and use a viewport. Then, rather than actually scaling the drawing for plotting, you zoom within your viewport to get it at the scale you need. Actually, I don't even put my linework in the same drawing file as my border. I actually do my linework in a seperate drawing (in model space), then xref my border into paper space. If you don't use model space/paper space I may have just lost you, but it works the same if everything is done in model space. If you only work in model space, I'd xref my linework drawing into my border drawing (you have to scale the xref). Man, this would be alot easier if we were both sitting in front of the same computer with ACAD open. Anyway, the point is this...regardless of which technique you use, if you are going to have text in your drawing, be it labels or only in the border, you need to know what the final plot scale will be and set up your text heights accordingly or you may end up having to redo alot of text (yes, I have learned this the hard way after deciding I needed to change the scale of my drawing after I had done all of my labeling). The key here is always think ahead and plan your final product before you start drawing lines on paper (so to speak).

One other thing....

I usually draw everything in decimal feet, so if I measure a line and ACAD returns a value of 323.25, I know it is 323.25 feet long; however, when drawing details, structural drawings, etc., I often need my units to be in feet and inches. In this case, you have to set things up a little differently. I end up drawing in inches rather than feet, so if I measure a line that is 12 units long, I know that it is 12&quot; (one foot). This is important when using the dimensioning commands, offset command, etc.. The only bad thing about architectural units is roundoff error and figuring out the scaling factors for plotting as described above.

Well, I didn't mean to ramble on so long. Good luck, and I hope this helped!

 

[pardal]

i want to keep track of this topic.

You can reach me at k281969@hotmail.com
but keep your post here for mutual benefits.
Pardal

 

[Sirius]

Right, my two pence worth..........

You say that your engraving software inputs it at the wrong scale - this is most likely the input translators on your engrave software. I have the same trouble with Teksoft, a file we get sent (apart from linetypes/layers/colours going all wrong etc) which is suppost to be in metric comes in 25.4 times too big or small!!!. Other softwares work fine. Its crazy!.

If you only use model space for your work (as many autocad users do because they dont understand paperspace techniques) then an easy way to convert your drawings is to start a new empty file with the option of 'metric' or 'inches' on starting - then go back to your original file and copy to clipboard all your work, switch back to your new file and paste it in. Hey presto all your imperial work should be metric now (eg 25.0&quot; is now 25.0mm). Havent done it for a while but I remember it working to this end.
This would only be useful for when the 'unit length' is the right value but in the wrong measurement system (metric/imperial) obviously......

When is imperial measurements going to die? thats my question!. Older fashioned companies in England are still stuck in imperial and first angle draughting and of course the Americans!!.
Didnt some space project go 'tits up' because us europeans were in metric and the U.S was still using imperial!!! Bonkers.
Mind you, saying that, if somebody asked me how tall I was I would say &quot;5 foot 9 inches&quot; and wieghed 11 stone. Its the era I was educated in I suppose - where folk could not make thier minds up what to teach us in schools!!
Metric and third angle is the only way!!! heheheh.

Hope the tip works for you, I use Acad2k by the way.......paperspace has vastly improved in R2000 than release 14!!!! If youre on 2000, count yourself lucky if you get into it!!.


See ya,

Sirius.