Model - Precision of created objects

[Anonymous]

What I've done:

I created a Box with dimensions (length x width x height) 10x10x10 mm.

Problem:

Box is not exactly the size which is shown in the preview before.

In special the length and the width of the box are not equal 10.0 mm at the end, although my mouse was snapping to the grid and it was correctly shown in the preview dialog. At the end the width and height is 10.000000149 mm instead of 10.0 mm.

[James.Youmatz]

Hi @Anonymous,

Thanks for posting! I believe this has to do with the precision of Fusion in general. Fusion is precise out to the Micro level, not the Nano, even though we can display that many decimal places. 

Thanks,

[Anonymous]

Hi @James.Youmatz,

why is then the 'Nano Level' not truncated of the floats used to describe and calculate everything. All methods of the API and functions done via the UI are using the 'nano level' instead of ignoring it?

e.g. if you want to compare two points with the Point3D isEqualTo() method of the Fusion API the nano level makes a difference which makes no sense at all!

Greets Fabi

[James.Youmatz · Accepted solution]

Hi @Anonymous,

Good call - we tested around with this a bit more and I see what you are saying now. It has to do with snapping to the origin. If I create a line (without snapping to the grid at all), make it 10.0, and then inspect the line, it is accurate. Then I can go ahead and place a coincident constraint to put it back on the origin. This seems to work. I'll log this bug with high priority. 

Thanks,

[jeff_strater · Accepted solution]

One small comment to add in addition to what @James.Youmatz said.  This problem only seems to occur if you rely on grid snapping.  Completely agree that grid snapping should be more accurate than that, but when I want completely accurate values, I always type in numbers into the input entries.  If you do that, the cube does come out exactly to the dimensions entered.

Just if you were looking for a way to get better results...

Jeff

[Anonymous]

@James.Youmatz Thanks for logging it!

@jeff_strater yeahh you are right, Thank you very much. The problem is that many beginners watching my videos are not going to enter the exact dimension, because they seem to be exact on the first preview and it saves time to not enter the values. Later on you are surprised on that, especially subsequent faults would be not negligible.

I also created an Idea adsk.com/api-point3d-use-isclose-in-isequalto onto the Fusion IdeaStation. My advice is to compare floats with isclose() instead of '==' or you could also multiplicate the floats with the micro level and do an integer equation.