ibach Posted June 12, 2013 Author Share Posted June 12, 2013 That's what I'm aware off, but i ve newer seen it happen in non rotated rectangle whose sides are exact round numbers before version 2014 (do not know about 2013) I just drew the same thing in version 2014 beginning at the 0,0,0 and in world coordinate system, and got the same error, +0.00000002 What's wrong about binary representation of round numbers?! Quote Link to comment Share on other sites More sharing options...
ibach Posted June 12, 2013 Author Share Posted June 12, 2013 Moreover, If I convert it to region, area is calculated correctly! ........................But when I rotate that region, error is back... (which is ok I suppose...) Newer mind rotation... Why does autocad calculates the same surface area at the same place, same points, same geometry, same rotation differently if it is a polyline or the region?! Quote Link to comment Share on other sites More sharing options...
ibach Posted June 12, 2013 Author Share Posted June 12, 2013 And more... When I do the UNDO of that rotation shouldn't I get the same region sa before... NO I get error of .00000006 after UNDO!!! Doesn't UNDO mean I did nothing to the region at all?! No it obviously does not! There is something terribly wrong here... I need to know what. Side lenghts and vertex positions are still the same, only the area is different. No I do not get it. Quote Link to comment Share on other sites More sharing options...
nestly Posted June 12, 2013 Share Posted June 12, 2013 So lets assume that Properties uses a different method for calculating polyline area than the AREA command. Are you opposed to using the AREA command if it always returns the correct value (out to 8 decimal places), compared to the Properties palette which does not? Quote Link to comment Share on other sites More sharing options...
ReMark Posted June 12, 2013 Share Posted June 12, 2013 Why are you using AutoCAD to model molecules? That does not sound like the right tool for the job. Quote Link to comment Share on other sites More sharing options...
ibach Posted June 13, 2013 Author Share Posted June 13, 2013 ReMark, you are right, but we live in upside down world... I work for 10 months without pay. Why do I work at all?! nestly, that's just it, I'd love to know both methods used, to be able to compare results. Quote Link to comment Share on other sites More sharing options...
nestly Posted June 13, 2013 Share Posted June 13, 2013 Perhaps Properties just calculates on fewer decimal places. You can find threads at any AutoCAD forum about autocad freezing even high end computers when selecting complex polygons with the property palette open. This is due to the automatic area calculation that occurs when a polyline is selected. My advice is to set units to 7 decimal places, so you see all zeros in properties and call it a day, because now that you know that 0.00000000 may or may not be exactly zero, you're going to start wondering what the 9th digit is, and if it is zero, what's the 10th 11th and 12th...... Quote Link to comment Share on other sites More sharing options...
RobDraw Posted June 14, 2013 Share Posted June 14, 2013 Why are you using AutoCAD to model molecules? That does not sound like the right tool for the job. +1 One of the definitions of insanity is doing the same thing and expecting different results. AutoCAD is actually giving different results for what we all know is the same rectangle. You've may have proven that AutoCAD is insane. I think that you've also proven that, for this type of precision, it is crazy to use AutoCAD. Quote Link to comment Share on other sites More sharing options...
SEANT Posted June 14, 2013 Share Posted June 14, 2013 (edited) At least use the appropriate unit. Nanometer or Angstrom would make better use of 16 significant digits. Edited June 14, 2013 by SEANT Quote Link to comment Share on other sites More sharing options...
neophoible Posted June 14, 2013 Share Posted June 14, 2013 I have not seen where AutoCAD promises to be accurate to that many decimal places, especially when it comes to calculations beyond graphical position. And eliminating computational error on computers is not really possible, even for graphical position. stephen-g's link explains that. Binary cannot represent every number perfectly; neither can decimal. Numerical methods to predict and minimize error are complicated, and can be very time-consuming. If you need a high level of computational accuracy, you will need to have someone involved who knows how to handle it expertly, and don't forget the computers and software to achieve it. Perhaps, as ReMark suggested, there are expert tools to get you there without that personal expertise. On the other hand, if you really want to be sure, make all of your calculations by hand. I recall an anecdote about a father and daughter balancing their checkbooks. She used her calculator to check her arithmetic. He checked the calculator by hand. In other words, she trusted the calculator more, he trusted himself more. Quote Link to comment Share on other sites More sharing options...
ReMark Posted June 14, 2013 Share Posted June 14, 2013 ChemDraw Pro 13.0 from PerkinElmer for chemical structure drawing and analysis. ChemSketch? Quote Link to comment Share on other sites More sharing options...
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