[Yt-dev] Volume rendering with current (3628:da3894bf42a5) change set

[Matthew Turk]

Hi Chris,

On Tue, Jan 4, 2011 at 7:21 AM, Chris Malone <chris.m.malone at gmail.com> wrote:
> Hi Matt,
>
>> >
>> > After using the debugger as you suggested and looking more closely it
>> > seems
>> > that LE is still an empty list because self.bricks = None even after a
>> > call
>> > to self.partition_grids().  The latter is not working properly because
>> > self._brick_collection.source._grids is an empty ndarray.  For example,
>> > I
>> > get the following DEBUG message before the fatal error:
>> >
>> > yt         DEBUG      2010-12-30 16:40:49,932 Preloading ['Density']
>> > from 0
>> > grids
>> >
>> > I now need to track down why _grids is not being filled appropriately;
>> > all
>> > the other grid-type-lists I have found are properly filled.
>>
>> My guess is actually the width argument -- you're setting it to 1.0,
>> and the center to 0.5, 0.5, 0.5.  Can you try with:
>>
>> W = pf['unitary']
>> c = 0.5*(pf.domain_right_edge + pf.domain_left_edge)
>>
>> which should grab all the bricks?
>
> Ok, that makes a bit more sense - I always thought the width and center
> values were relative coordinates.  Fixing c to be the physical center of the
> domain worked, but I had to modify W to be the physical width:
>
>     W = pf.domain_right_edge - pf.domain_left_edge
>
> to grab the bricks.  As far as I can tell with all the other frontends,
>
>     pf['unitary'] = (1.0 / (pf.domain_right_edge -
> pf.domain_left_edge)).max(),
>
> which is a a pretty small number.  With these fixes I'm at least getting a
> volume rendered image, but I'm not sure exactly what it is - it looks
> strange, but I'll play with the transfer functions and such to see if I can
> quantify what I mean by "strange."

Ahhh, I messed up -- it should be

1.0/pf['unitary']

It's also possible something funky is going on, so if you'd like, feel
free to send some images and the TransferFunction instantiation so we
can take a whack.  I think it's pretty important that we have an
intuitive interface to volume rendering!

-Matt

>
> Chris
>
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