[yt-dev] Orientation, coordinate systems

[Michael Zingale]

Matt, does this explain why in a notebook the orientation of a volume
rendering resulting from cam.show() is wrong compared to when you do
write_png() on the result of cam.snapshot()

(I see gravity going sideways instead of vertically in one of my plots)


On Tue, Apr 15, 2014 at 11:47 AM, Matthew Turk <matthewturk at gmail.com>wrote:

> Hi everyone,
>
> Here's step one:
>
>
> https://bitbucket.org/yt_analysis/yt/pull-request/821/abstract-out-all-axis-information/diff
>
> -Matt
>
> On Fri, Jan 31, 2014 at 12:03 PM, Matthew Turk <matthewturk at gmail.com>
> wrote:
> > Hi all,
> >
> > On the hangout today we talked about this and I did some digging into
> > how yt manages arrays, and how this comes out in matplotlib.
> > Basically, there are two things going on.
> >
> > One is: what do we want our pixel coordinates to be?  When dealing
> > with images, typically [0,0] is the upper left of the *image*.  This
> > is also what yt does -- except, it corresponds to the origin in the
> > coordinate system.  Basically, our origin corresponds to the origin,
> > but in images, this is y-axis flipped.
> >
> > Fortunately, matplotlib handles this gracefully with an origin=
> > keyword.  You can state that origin='lower', which flips the y-axis of
> > the image, thus putting 0,0 at the bottom left.  This works if you
> > only care about using matplotlib to plot things -- but if you want to
> > take your image buffer somewhere else and save it, it's now opposite
> > what you'd get out of matplotlib.
> >
> > And thus we enter into the issue of the volume rendering, which we
> > typically save out using a direct png writer, which by default will
> > flip the axes and write it out.  But I'm wondering what the right
> > approach is.  I see two options:
> >
> >  * Fix the way we pixelize images so that the *lower left* matches the
> > origin of the coordinate system.  We would no longer use
> > origin='lower' in our matplotlib calls.
> >  * Use origin='lower' everywhere, and assume that FRBs and whatnot
> > will be correctly pixelized by the individual getting them back out.
> >
> > I am inclined toward the first option, but because it's invasive and
> > actually changes the way our images are generated, I wanted to get a
> > feeling from the group.  We're now breaking convention somewhat, and
> > our integer and coordinate system values won't match up in the y axis
> > anymore.
> >
> > -Matt
> >
> > On Fri, Jan 17, 2014 at 1:45 PM, Cameron Hummels <chummels at gmail.com>
> wrote:
> >> I agree with Nathan.  I filed a bug to this effect a few weeks ago
> >> demonstrating that one gets different orientations (transposes) out of
> the
> >> volume rendering infrastructure than out of the Projection
> infrastructure
> >> with the same inputs.  This is very confusing and I think should be
> >> remedied.  Good call, Matt.
> >>
> >>
> >> On Fri, Jan 17, 2014 at 11:38 AM, John ZuHone <jzuhone at gmail.com>
> wrote:
> >>>
> >>> On Jan 17, 2014, at 1:35 PM, Nathan Goldbaum <nathan12343 at gmail.com>
> >>> wrote:
> >>>
> >>> To clarify further: I'd ideally like to see these two function calls
> >>> produce identical plots:
> >>>
> >>> ProjectionPlot(pf, 2, 'Density')
> >>> OffAxisProjectionPlot(pf, [0,0,1], 'Density')
> >>>
> >>> without having to specify a north_vector by hand for the second plot.
> >>>
> >>>
> >>> This is my biggest reason for wanting to see this fixed.
> >>>
> >>> _______________________________________________
> >>> yt-dev mailing list
> >>> yt-dev at lists.spacepope.org
> >>> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
> >>>
> >>
> >>
> >>
> >> --
> >> Cameron Hummels
> >> Postdoctoral Researcher
> >> Steward Observatory
> >> University of Arizona
> >> http://chummels.org
> >>
> >> _______________________________________________
> >> yt-dev mailing list
> >> yt-dev at lists.spacepope.org
> >> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
> >>
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>



-- 
Michael Zingale
Associate Professor

Dept. of Physics & Astronomy * Stony Brook University * Stony Brook, NY
11794-3800
*phone*:  631-632-8225
*e-mail*: Michael.Zingale at stonybrook.edu
*web*: http://www.astro.sunysb.edu/mzingale
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