Databases and Units

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Anthony Bavuso (a.t.bavuso++at++larc.nasa.gov)
Mon, 20 Dec 1999 13:16:45 -0500

I have another question related to my previous question about open flight
databases and units. Thanks to a very informative response from Calvin Lu,
I can now at run-time ask a database what physical units it uses. But then
my problem is what do I do with that information. I need to get all of the
models to use one consistent physical unit so they all are of the
appropriate sizes. There are several obvious possibilities.

I could for example place a pfSCS node above my geometry scaling it to the
desired units. But then would I take a run-time hit whenever I traverse my
model scene graph to convert the model units into the desired units through
the pfSCS node. This is of course undesirable.

What I would like to be able to do is once immediately after loading the
model to alter the loaded geometry to use the desired units. In other words
I would like to load into memory the geometry in its native units; scale it
to my desired units; and then replace the original geometry in memory.
Therefore every time I traverse the scene graph of the model it is
inherently in the desired units.

How would I do this?

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