Re: 3D symbols for point data: spheres and beachballs

• To: Stuart Wier <wier@xxxxxxxxxx>
• Subject: Re: 3D symbols for point data: spheres and beachballs
• From: Bill Hibbard <billh@xxxxxxxxxxxxx>
• Date: Thu, 7 Oct 2004 13:59:10 -0500 (CDT)

Hi Stuart,

> Needing to make small 3D symbols for point data, spheres in particular,
> I am using code like that in the ucar.visad package, class
> ShapeUtility.java, which creates VisADGeometryArray-s by specifiy the
> xyz locaiton of every vertex, and a normal for each vertex and face.
> See the 3d pyramids in the figure at the bottom of
>   http://geon.unavco.org/unavco/IDV_for_GEON.html
> The VisADGeometryArray and the ShapeUtility code allows the
> needed feature of resizing the shape and setting a color.  But making a
> sphere looks difficult, since it is not a simple
> polygon with flat faces. Has someone a solution?

In OpenGL and similar 3-D graphics libraries, smooth shapes
like spheres are constructed with large numbers of flat
triangles. The larger the number of triangles, the smoother
the appearence.

> Looking ahead, I need to color the sphere in panels (gores) like a
> beachball for earthquake focal mechanisms. See
> http://quake.wr.usgs.gov/recenteqs/beachball.html
> Any ideas?

You can construct a VisADTriangleArray, with different
colors for different triangles. The key is to avoid any
of the TriangleStrip classes, since they share vertices
among triangles that may not have the same colors.

Good luck,
Bill

• References:
  • 3D symbols for point data: spheres and beachballs
    • From: Stuart Wier