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  1. #1
    Luminous Being tzframpton's Avatar
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    Default Possible AutoCAD inaccuracy?? (DWG Included)

    I have an issue that my boss came to me about. He created a polyline tracing over some architectural rooms to create a zone for an HVAC load calculation. Nothing fancy just a simple PLINE, and took the area. Later, he decided he wanted to split it into two zones. He took the area's of each zone, then added them together to double check his work and it came out a different number than the original single zone. I have attached the file for clarity, but here's the breakdown:
    • Single zone is 5,501 sq ft.
    • Separated zones are 4,062 sq ft. & 1,177 sq ft.
    • Add 4,062 + 1,177 = 5,239 sq ft????
    Nothing literally changed between these two zones, there is simply a line that divides them into two separate zones, that is it.

    At first guess, we thought maybe AutoCAD formulates the area calculation from the perimeter and uses some type of conversion method to produce this number. I tested a PLINE where I actually overlapped a few lines, but I found that AutoCAD is definitely smarter than that, it still took the literal area of it even though the length of the PLINE was inaccurate due to the overlapping lines. My boss (who's also the vice president of engineering) is stumped by this. He just cannot understand how AutoCAD is producing this number, and where the loss is. I'm hoping someone out there might have a clue as to what is happening here. Thanks in advance for anyone who might be able to help!!
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    Revit & AutoCAD "In fact I find AutoCAD to be a very frustrating experience now." -Steve Stafford

  2. #2
    Quantum Mechanic ReMark's Avatar
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    Default

    And everyone is using the same software (MEP 2010) right?
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  3. #3
    Super Moderator Tiger's Avatar
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    Default

    The Area that shows up in Properties on the smaller (1177 sq ft) and the area that I get from AREA-command are not the same...the AREA-command gives the correct amount (ie added with the bigger area equals the non-divided area) - but why that is, I have no idea.

    Update, if I draw a new PLine over the smaller area, THAT comes up with the right Area in Properties I wonder how the lines where divided, Break?
    whether is when you are asking yourself, should I stay or should I go
    weather is when it's cold as all that outside
    wether is a goat soprano
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  4. #4
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    Default

    The smaller area is not drawn right. If you do a pedit, and close the polyline, you'll see that it is not drawn correctly. Create a new boundary (BO command) and do an area on the newly created boundary, and you'll see that it produces the correct area.

    HTH

  5. #5
    Quantum Mechanic ReMark's Avatar
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    Default

    Oops. Sounds like the boss needs some training on the use of Osnaps.
    "I have only come here seeking knowledge. Things they wouldn't teach me of in college." The Police

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  6. #6
    Super Moderator Tiger's Avatar
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    Default

    If I step through the Vertixes on the PLine (Pedit > Edit Vertix > Next ..) , after it comes to the end, it goes back and overlaps itself....
    whether is when you are asking yourself, should I stay or should I go
    weather is when it's cold as all that outside
    wether is a goat soprano
    #SpellingMatters

  7. #7
    Luminous Being tzframpton's Avatar
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    Default

    Ah!! So that's it.... I told my boss that I have seen in the past arguments relating to AutoCAD's accuracy and that it cannot be beaten. I even thought about using the BOUNDARY command to test, sometimes I guess I jump the gun in my questions before I seek the answer myself. Once again, thanks a lot guys.
    Revit & AutoCAD "In fact I find AutoCAD to be a very frustrating experience now." -Steve Stafford

  8. #8
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    Default

    So, it was operator error or boss error
    Please do not PM me with CAD questions. Post your question on the forum. Our users are the best out there and you'll get the best possible answer to your question.

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  9. #9
    Luminous Being tzframpton's Avatar
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    Default

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    Boss Error for sure.
    Revit & AutoCAD "In fact I find AutoCAD to be a very frustrating experience now." -Steve Stafford

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