[yt-users] opaqueness of iso-surface

[Sam Skillman]

Hi Renyue,

It turns out that's not such an easy thing to do at the moment.  Because of
the way the transfer function was constructed, most of the renderings turn
out to live in an optically thin regime.  This is primarily due to the
adaptive nature of grid traversal and the clipping of the transfer function
to have a maximum value of 1.0 and the way the integration is approximated.
 I've added some changes to this in a bitbucket fork that is part of an
effort to refactor the volume rendering.  If you'd like to try it out, you
can clone this fork from:

https://bitbucket.org/samskillman/yt-refactor

Note that this also brings with it some OpenMP stuff, and by default it
runs with OMP_NUM_THREADS = number of cores the node.  You can get rid of
this with export OMP_NUM_THREADS=1.

Because of the adaptive nature of our ray-casting, you may need to set
alpha to something higher than 1.0 (since it get's multiplied by something
like dx during ray tracing).  You can find an example script of mine where
I add three isocontours, as well as use a camera lighting (yet another
feature in the works).

http://paste.yt-project.org/show/2244/

Let me know if you have any luck/difficulty with this.  We will be pushing
for this in the next stable release.

Best,
Sam


On Tue, Mar 20, 2012 at 10:37 AM, Renyue Cen <cen at astro.princeton.edu>wrote:

> Hi,
>
> For  iso-density surface I have a primitive question: how do I make
> certain contour level totally opaque?
> I can do " tf.add_gaussian(-25.5, 0.05, [1.0, 0, 0, 1.0])"
> but specifying alpha=1.0 in this example does not seem to make that level
> (red) totally opaque.
>
> Thanks,
> Renyue
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