RE: partially buried contours

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

-----Original Message-----
From: Bill Hibbard [mailto:billh@xxxxxxxxxxxxx]
Sent: Tuesday, January 07, 2003 12:24 PM
To: Donna L Gresh
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,

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
> 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