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Make ETO accuracy consistent to something

Make ETO accuracy consistent to something

This one might be hard to explain.  And a bit picky, but oh well.

I have a part that is 136.1875 inches long.

I want to scale the part down to be exactally 10 inches on my drawing.  So I apply the formula 1/(136.1875/10) to get the scale to apply to the view.

My viewscale that I see in the intent model properties is 0.07342817806333 which is close to the number I get with my windows calculator(0.07342817806333180357962368058743).  

However, when I look at the intent model width property I see a value of 10.0000000005782.  When I use 0.07342817806333 * 136.1875, my windows calculator shows 9.999999999999754375.  When I use 0.07342817806333180357962368058743 * 136.1875, my windows calculator shows 10.000000000000000000000000000001.  Where did 10.0000000005782 come from?

 

Anyway, I'm wondering if this has anything to do with the intersection of inventor accuracy and ETO accuracy?  Inventor's 100 millionth vs ETO's 10 trillionth = inconsistancy

 

~Andrew

4 Comments
JackGregory
Alumni

Ah, floating point math.  One of my favorite subjects.

 

First, I am sure you are aware that our display of numbers is not the same as what is actually in the value.  So when you look in Intent model properties, we aren't showing all the decimal places.  So using that number in a further calculation is obviously going to round off.

 

But, I want to drill down and nail this, so I am going to be careful and ask you precisely where (in the user interface) you are taking / seeing the 10.0....5782 value from?  And what version of ETO is this on?

 

Finally, where are you basing "Inventor's 100 millionth" accuracy on?  Internally, ETO uses IEEE double-precision floating point ("double") for real numbers.  Inventor can't do any better.  It is possible you have discovered a real bug here, which I would like to investigate, but right now it feels like a displaying issue, not a real internal accuracy issue.

JackGregory
Alumni

I tried this using these dynamic rules:

 

Rule scaled As Number = 1/(size/10)
Rule size As Number = 136.1875
Rule scaled_back As Number = scaled*size

When I look at scaled_back in the properties window in Inventor, I see a perfect 10.0

 

Let me know what might be different from what you are looking at.

alundr
Advocate

viewModel.width = 8.14503175473055  'pulled from intent model browser

viewModel.height = 2.125

 

Rule viewScale As Number

    Dim StartingScale As Number
    Dim EndScale As Number
    StartingScale = 1/(viewModel.width/10)
    If viewModel.height*StartingScale > 6 Then
        EndScale = 1/(viewModel.height/6)
    Else
        EndScale = StartingScale
    End If

    Return EndScale
End Rule

 

'EndScale = 1.2277422975290555097497227630025  according to Windows calculator

 

Child LengthView As :LengthView
    Model = viewModel
    viewscale = viewScale
    viewOrientation = (If viewModel.Hand = "Right" Then :Back Else :Front)
    rotationAngle = (If viewModel.Hand = "Right" Then 90 Else 270)
    origin = (If viewModel.Hand = "Right" Then Point((17),6.5,0) Else Point(3,6.5,0))
    showViewLabel? = True
    ViewLabelPosition = lengthView.origin + (UnitY*(((viewModel.height*viewScale)/2)+.25))
End Child

 

And this is what I see in my model browser.

Accuracy Intent Model.JPG

 

alundr
Advocate

Win 7 Pro 64bit

Dual Intel Xeon E5645 

12GB ram

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