Geometrical Normals in Alias 2017

[DavidPBP]

Hallo,

I have an issue with the new surface orientation tools of Alias. It is not a real bug, Alias works as it ever does, but is it correct?

In older Alias-Versions the Data-Translotor adjusted the geometrical normals automatically to match the visual normals, set with the surface-orientation tools.
One can argue that this data-translation changes the surfaces in some way, and that is generally wrong.
On the other hand it was very comfortable, not only because it wasnt easy to see the geometrical normals, but also because the geometrical normal of a surface affects many Construction-History elements. Changing them could mess up the whole model.

Now in the new Alias 2017 there is the possibility to adjust geometrical normals easyly. Thats good, I first thought.
But now I discovered the data-translation still changes the geometrical normals based on the visual ones. So the new tool isnt really useful.

In my opinion (and my collegues agreed with that) the exported normals should be the geometrical normals ones.
Is this feature of the Data-Translator still wanted, or should it rather be updated to match the new surface orientation possibilities? Please comment!

Kind regards, David

[duaxiong]

In there a particular reason you would want exported Normals to be different than the visual ones?

[DavidPBP]

The visual normals are just in-Alias Software-defined normals, for shading purposes (i.e. texturing and diagnostics). Other CAD-Software just didnt know these type of normals.

The geometrical normals are mathematically defined with the UV-direction of a surface. These are the normals every other CAD-Software will understand, because all CAD-Software is based on the same surface-mathematics.

Only in Alias it is necessary to differ between these two, because the UV-direction also affects the Construction-History. But for exchange to other software the visual normals doesnt really matter.

In Former Alias-Versions it wasnt easy to see the geometrical normals. So it was useful that the Data-Translators changed them based on the visual normals.

But with that, the Data-Translator changes the mathematical definition of a surface, with changing the UV-direction. And that is generally wrong.

Now finally with Alias 2017 there is the possibility to adjust the geometrical normals easily in Alias.

So why still exporting the visual normals? It would be more logical to export the 'common-CAD' geometrical normals directly.

[duaxiong]

So...you would prefer to flip the geometric Normals yourself, rather than have the export translator do it automatically...?

Is the translator deviating that much when it flips the UVs?

I wonder if the translator is using the same algorithm as the Set Geometric Surface Orientation function.  

In any case, it should be easy enough to add in an option for this on the exporter; Maybe put in a request in the next beta cycle.

[DavidPBP]

There are no deviations in the surfaces. Thats not the matter. Its just a logical one.

Usually I check and adjust all the normals just before I export and send my data to other departments, so at the very end of my modelling process.

It doesnt makes any difference if than I have to check visuals or geometricals.

But while the visual normal are Alias-specific and all other CAD-Software is working with just geometrical normals, for me it would be logical to adjust the geometrical ones before exporting the data. 

Also the geometrical normal with its definition affects the visual normal, but not the other way. So the geometrical is in some way the more important of the two, the first one I would choose to adjust.

But its a good hint to post it during the next beta-cycle, I'll do that. Thanks!

[duaxiong]

Personally, I'm fine with the way it works currently;  I think it may confound some people when they Export only to find that their Normals are not pointing the way that they set them in Alias.

[DavidPBP]

I was fine with the "old" way, too. As there wasnt any choice.

But I think the main reason for this new introduced difference is to easily unify the mathematically defined / geometric normals for better data-translation. Because other CAD-Programms only understand the geometric normals, while in Alias itself I cant see any further advantage.

Therefore for me its strange that the data-translator still refers to the visual normals only.