How to access Facet Data in a 3D surface

• To: visad-list@xxxxxxxxxxxxx
• Subject: How to access Facet Data in a 3D surface
• From: "Developers" <developers@xxxxxxxxxxxxxxxxxxxx>
• Date: Fri, 02 Aug 2002 17:32:19 GMT

Hello, 

I am working on a project in which we are using VisAd to display a 3
dimensional image of data points.  We essentially create a 3d surface out
of these data points, which are made up of triangular facets, made out of
the data points.  My question is pretty simple, but I am having a really
interesting time figuring out how exactly VisAd creates all of these
triangular facets, and how to access those facets.

Essentially, I want the user to be able to click on the screen somewhere
and be able to report what facet the user clicked on, and report any data
associated with that facet. What I can't figure out is how VisAd stores the
data associated with the facets that it is drawing.  

I have looked into MouseHelperJ3D and I see how to get the location in
world space of the observer (eye_position) and how to get the location in
3D space that the user clicked on (position).  I can create a vector out of
this and this is my ray in 3D space.  I want to know if that ray,
emminating from the observer, going out into space, intersects with any of
the facets in the data set we are displaying.

I have looked into the following classes and elucidated the following (tell
me where I am incorrect):

FlatField is a container for the entire "data model"?
DataReferenceJ3D setData() is a gateway of some kind in setting the data
for each of the facets in the 3D surface?

The confusion I encounter is that when I try to go past the
DataReferenceJ3D, it starts referencing an object called "Thing".  I am
having difficulty understanding exactly what a "Thing" is.  Is it in any
way related to how I access where the facets are in 3D space?

Typically in 3D graphics one uses some kind of data structure to hold all
of the facets in an object.  I understand this could be different for
Java3D, but essentially, the data for displaying the facets has to be
stored somewhere, and there has to be a way to access it.  Im just having
difficulty finding it.

If anyone has any suggestions where to look to find out about this, I would
be very appreciative.



Cheers, 


Greg

• Follow-Ups:
  • Re: How to access Facet Data in a 3D surface
    • From: Bill Hibbard