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 From:  yannada
2503.1 
Please tell me that's a graphics card issue. I get that all the timr, the more complex the geometry the more visable they are...
graphics card_Quadro FX 350M

example_001

example_002

EDITED: 17 Apr 2009 by YANNADA

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 From:  Michael Gibson
2503.2 In reply to 2503.1 
Hi Yannada, these are a variety of tolerance and precision issues, nothing really out of the ordinary for either one but they are some slightly different things.

When you go to an extreme zoom level, you can usually expect for the shaded mesh display to start to lose precision and you can kind of see the limits of floating point numbers. The mesh will kind of "snap" to a smaller number of locations.

That's something that is a graphics card issue but it is common to all graphics cards and not just your particular model - it is because graphics cards use "single precision" floating point numbers for their mathematics, which have some limited precision but are also faster and use less memory.

Note that you have zoomed in by an extreme amount, so that the distance shown here is really very small:



You can generally expect that operations in MoI that involve fitting will get a result accurate to within 0.001 units, which is pretty much the same (or more accurate) as what is commonly done with most CAD systems.

It's normal for there to be gaps or overshoots on edges, as long as they are all under that tolerance level.

In the case that you show there, 0.000002 is clearly at a higher level of accuracy than 0.001 so no real problem at all there...

This process is done by all software that performs intersections on NURBS surfaces. Otherwise to get higher accuracy than that would cause the curves to become so dense with control points that the data size for models would go up by like a factor of 10 or 100, making models unwieldy and requiring too long to do the calculations.

So anyway that is something that is totally normal, other CAD systems will also generate the same kinds of tolerance levels and will expect to be able to handle things of that level of accuracy.

If you get things that look like misalignments that are of a much larger size than that, like larger than 0.001 units, then those would be more of something to worry about.

- Michael

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 From:  yannada
2503.3 In reply to 2503.2 
Oh thanks Michael I feel better now.
Also If I remember correctly in Solidworks I could adjust that which help me to sort of inspect the model, are there any settings in MoI?
As well when I demoed Rhino I think I could change the tollerance to 0.0001 etc. Or was that a geometry tollerance? I'm not sure.
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 From:  Michael Gibson
2503.4 In reply to 2503.3 
Hi Yannada, no there isn't currently any way in MoI to adjust it.

That is possible to do in Rhino and it tends to cause several really weird problems.

For instance, if you receive a file from someone else and you don't happen to be aware that they set the file tolerance to be really loose, it is very surprising when you try to create a new object after having opened that file and see things like big gaps or saggy parts in intersections or fillets. It's really hard to figure out what is going wrong and it is not so easy to remember to check the tolerance.

Even if you set it yourself some time ago it is something that is hard to remember.

So I didn't want to get into those same kinds of problems.

Maybe in the future I can allow some kind of adjustment that will only last for the next operation or only during the current modeling session and not get stored in the file, that may be a possibility later on.

Also another issue is that I want to move to not have a totally fixed tolerance and instead have it adaptive to the overall size of the object. There are just a couple of things that do this currently like Join and Network but I want to add more things that follow this in the future because otherwise it doesn't really work very well with the tolerance being too tiny in comparison with the objects. Like if you have objects that are around 20,000 units in size, then 0.001 is too small in comparison to that, you end up with the same kind of "extremely heavy intersection curve" type problem.

- Michael
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Message 2503.5 deleted 22 Mar 2009 by YANNADA
 

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