RE: partially buried contours

Interesting suggestion, Craig, but to work on a point by
point basis it has to be implemented in the 3-D graphics
API. You may want to make your suggestion to the Java3D


On Tue, 7 Jan 2003 Craig_Barrington@xxxxxx wrote:

> Hi Bill and Donna,
> I'm just a casual observer; somewhat interested in Visad.
> I'm not sure who the developers are, or if they are "listening", but this is
> mainly to them.
> I'm just guessing that the logic that Visad uses to determine if the contour
> lines are visible needs to be changed to be much simpler as follows:
> Visad must have an algorithm that determines whether a point on the surface
> is visible.
> If that point is (would be) visible, then a contour line on the surface at
> that point is visible (instead of the point).  That is the basic idea.  i.e.
> The surface is drawn, and then the contours are drawn, using the same
> algorithm to decide on visibility as the surface itself.
> Well, as I said, that's the basic idea I wanted to suggest to the Visad
> developers.  It might save everyone a lot of futzing around with ad hoc
> hacks (Hey, how about "ad hacks"?).
> Craig Barrington
> Fluor Federal Services
> Richland, WA
> 509-373-0946
> Craig_Barrington@xxxxxx
> -----Original Message-----
> From: Bill Hibbard [mailto:billh@xxxxxxxxxxxxx]
> Sent: Tuesday, January 07, 2003 12:24 PM
> To: Donna L Gresh
> Cc: visad-list
> Subject: Re: partially buried contours
> Hi Donna,
> I did a couple experiments and found something you can do, but
> its a bit of a hack. You can raise the contours away from the
> surface, if you can decide on a fixed direction for them to be
> raised. Say you decide to raise the contours by 0.02 in the
> positive ZAxis direction. Ideally, you could construct a
> ConstantMap of 0.02 to ZAxisOffset and include it in the call
> to DisplayImpl.addReference(). However, the system doesn't
> seem to pick up the ConstantMap to ZAxisOffset. So instead,
> replace your ScalarMap to ZAxis with an identical ScalarMap
> to ZAxisOffset, and use a ConstantMap to ZAxis in place of
> the ConstantMap to ZAxisOffset. Ugly, but it worked in a test
> I ran.
> Note that for 2-D displays, the system adds an implicit offset
> to raise line graphics above images and trianlges.
> Good luck,
> Bill
> On Tue, 7 Jan 2003, Donna L Gresh wrote:
> > I am adding IsoContours over a surface in three-space (an analog to
> > discussion in tutorial 3.7 of "IsoContours over image") and find that the
> > contours are partially "buried' in the surface. It is more or less obvious
> > depending on viewing angle. In my days of using Data Explorer there was a
> > way to add "fuzz" to the contours to allow them to "float" a bit above the
> > background object. Is there something equivalent in VisAD? Apologies if
> > it's documented and I just didn't see it; I did look in the javadoc and
> the
> > discussion.
> >
> > Here's a picture to show what I mean:
> > (See attached file: buriedcontours.jpg)
> >
> > Donna L. Gresh, Ph.D.
> > IBM T.J. Watson Research Center
> > (914) 945-2472
> >
> > gresh@xxxxxxxxxx