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When AutoCAD is not Accurate

June 2nd, 2009 | 4 Comments

precision When AutoCAD is not Accurate

CAD applications supposed to be accurate. And they are. But in some case, you might find AutoCAD to lost it’s accuracy.

concrete+hatch+error When AutoCAD is not Accurate
This hatch on the left is supposed to be conrete hatch. But as you can see, it doesn’t appear properly.
When you see errors like this, you might find that AutoCAD is no longer accurate.
I found that rotating objects with typing the rotation angle can be different to defining rotation angle by reference. Sorry, I cannot reproduce this error.
The problem is not in AutoCAD at all. It is the limitation of 32bit applications. You might find it in MicroStation too.
This might occur if you draw too far from 0,0. Many designer draw buildings by using global coordinate as reference. And it’s getting worse because we draw in metrics.
How we can avoid this? Just draw as close as possible to 0,0. Try to use reference and other units (m, km) to reduce large coordinate.

Illustration: http://www.sxc.hu/profile/kliverap

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Written by Edwin Prakoso

Application Engineer. Jakarta, Indonesia. 5+ years experience as CAD engineering application. AutoCAD, MicroStation, Revit, Inventor, and certified CATIA part design specialist. Here are some topics I am currently focusing on

Filed under: AutoCAD Troubleshoot

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4 Responses to "When AutoCAD is not Accurate"

  1. Eric Colburn says:
    June 3, 2009 at 1:53 pm

    You have touched on an important point by drawing attention to using large coordinates in an AutoCAD file (or for any other calculations, for that matter). Land surveyors sometimes work in assumed coordinate systems basing their work in low numbers, like N 5000, E 5000, and calculation errors will be smaller for this coordinate system, than say, for a state plane coordinate system where the points and drawing elements are, instead, located in the hundreds of thousands. i.e. N 3000000 E 300000.

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  2. Edo says:
    June 3, 2009 at 6:33 pm

    Thank you Eric. That's also what we do here. We tried to create a local coordinate to avoid this. But there are some architectural firm refuse to do this. They prefer to draw in mm for the building design in local coordinate, and then reference it to the whole site which is drawn in larger unit, ie. m or km.

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  3. Mike says:
    July 4, 2009 at 12:21 pm

    Currently finishing a Drafting degree with CAD specialization and we are taught to scale drawings so problems like this don't occur. An interesting point though. What is the exact error, or process that create these distortions?

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  4. Edo says:
    July 5, 2009 at 5:07 pm

    Mike,
    I won't suggest anyone to scale drawing in model space. Always draw real measurement on your model.
    Any modification can produce this error. I tried to rotate my drawings with reference, and rotate them back by keying in the angle… it won't come back to the original location. You might want to try to draw lines, and measure them. Try to draw them in millions unit away from 0,0.

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