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Message - Re: 3DMF response from Abvent

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Posted by  Kevin Matthews on March 09, 2001 at 17:46:29:

In Reply to:  3DMF response from Abvent posted by Jeff on March 09, 2001 at 13:34:56:

Okay, pull up a chair... Mike has already posted the concise "answer" in this case, but I thought you might like some more explanation.

About 3DMF files, the problem is that DesignWorkshop does not use the standard 3DMF format designed by Apple

Of course, we beg to differ...

...more precisely, DesignWorkshop uses kQ3UnknownTypeText to save the scale factor instead of using a kQ3TransformTypeScale object.

This is good, because here we are getting to the nub of the issue, and therefore the problem. There are serious language factors here, just within (technical) English, let alone to French which may underly the confusion.

So, to go on, we need to define a couple of terms, "scaling", and "units".

Scaling refers to changing the size of objects. It results in numbers, like the coordinates of objects in a 3D model, getting larger or smaller.

Units refers to a label that goes along with a batch of numbers, like the coordinates of objects in a 3D model. It gives us an external reference for the meaning of those numbers.

Those are our definitions for the purposes of this discussion.

Unfortunately the term "scaling" is thrown around rather loosely, so sometimes it is intended to mean 'scaling", as it should, and sometimes it is intended to mean "units", which gets confusing.

Apple helps this confusion, inadvertently, by using the name "ScaleAttribute" for the standard piece of custom data used to define the units of a 3DMF file.

For reliably controlled translation, the units are what you need to know. If the source and destination units match, then no scaling is necessary. If the source and destination units don't match, then the numbers that make up the model need to be scaled by the ratio of source and destination units.

Getting back to Abvent, inside a 3DMF file, the translation scaling issue does not actually involve scaling, but rather, it is a matter of "units".

In QuickDraw 3D documentation, one can read : 'Unknown Object are generated when reading files which contain custom data which has not been registered in the instantiation of QuickDraw 3D'. So the solution for you would be to save your model in cm, if it is possible, or to ask Artifice if the Scale Attribute is a really 'custom data', and what they suggest about it.

Yes, ScaleAttribute is really 'custom data', standardized custom data, which Apple defined in an official article in Develop magazine, as Mike already quoted in his message.

THEREFORE, the technically correct resolution to the "3DMF scaling problem" is for Abvent to read the ScaleAttribute units definer which is properly included in our 3DMF files, and then scale the incoming model to match whatever units they want to use inside Artlantis.

But don't tell them I said so!

; - )

Cheers,

K

 


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