[yt-dev] Vertex-centred AMR data?

Erik Schnetter schnetter at gmail.com
Wed Nov 11 06:55:07 PST 2015


Matt

For the moment, anything that works would be fine. I always selecting full
cells is easier I'd be happy to try this first.

-erik

On Wed, Nov 11, 2015 at 9:53 AM, Matthew Turk <matthewturk at gmail.com> wrote:

> Hi Erik,
>
> Thanks, this helps.  This means that for the specific case of your
> data, we will need to use a different selection method than that used
> for finite element data, where we select full cells rather than
> allowing partial selection.  Instead of "rounding up" we should be
> using a method similar to particle selection, where discrete points
> are sampled.
>
> For the case of changing a set of points into a pixel buffer, this
> means we will use nearest-neighbor interpolation (with no sub-cellular
> interpolation).  This should be straightforward, as it will suffice to
> define an edge of a zone (which will be truncated at boundaries) and
> width, which we do already for cell-centered data.
>
> On Wed, Nov 11, 2015 at 8:50 AM, Erik Schnetter <schnetter at gmail.com>
> wrote:
> > Matt
> >
> > In my notion, there are no cells, only vertices. Or if you want to
> renaming
> > things, then there are only cells, no vertices, but the fine a coarse
> grid
> > cells do not share faces.
> >
> > To answer your question specifically: no, it does not matter whether  the
> > centre of a "cell" is selected. Only the vertices that are selected
> should
> > be part of the selection.
> >
> > -erik
> >
> > On Wed, Nov 11, 2015 at 8:57 AM, Matthew Turk <matthewturk at gmail.com>
> wrote:
> >>
> >> Hi Erik,
> >>
> >> I have some ideas about this, but it relies heavily on the notion of
> >> how to regard "vertices" as separate from "cells", or if they should
> >> not be.  In terms of things like visualization, vertex centered data
> >> is not a huge leap in functionality, but in terms of data selection we
> >> need to be careful.  The canonical question is, if you have a region
> >> selector that includes the *center* of a zone, should all of its
> >> vertices be selected?  For instance, imagine you have a region
> >> selector whose corner resides at the center of a (3D) cell.  Does one
> >> select all eight vertices, since the "cell" is nominally selected, or
> >> just the one vertex that is included?  If we can answer that, we can
> >> start the work of implementing.
> >>
> >> On Tue, Nov 10, 2015 at 7:11 PM, Nathan Goldbaum <nathan12343 at gmail.com
> >
> >> wrote:
> >> >
> >> >
> >> > On Tuesday, November 10, 2015, Erik Schnetter <schnetter at gmail.com>
> >> > wrote:
> >> >>
> >> >> I have implemented a front-end for cell-centred Cactus AMR data.
> >> >>
> >> >
> >> > Awesome! We'd love to have this in the public distribution of yt.
> >> >
> >> >>
> >> >>
> >> >> However, many Cactus simulations use vertex-centred AMR. That is,
> data
> >> >> is
> >> >> stored at the vertices of a grid (not in the cells), and coarse
> >> >> vertices are
> >> >> at the same locations as fine vertices.
> >> >>
> >> >> How do I present such data to yt? Do I need to set grid coordinates
> >> >> differently, or is there a "vertex centred" flag?
> >> >>
> >> >> When vertex-centred data are displayed, then I expect either a
> "control
> >> >> volume" around each vertex to have the same value, or to use e.g.
> >> >> linear
> >> >> interpolation in the cells from the respective boundaries.
> >> >
> >> >
> >> > We don't have good support for vertex-centered AMR data. I think Matt
> >> > would
> >> > have a better idea of what approaches we might take here.
> >> >
> >> >>
> >> >>
> >> >> -erik
> >> >>
> >> >> --
> >> >> Erik Schnetter <schnetter at gmail.com>
> >> >> http://www.perimeterinstitute.ca/personal/eschnetter/
> >> >
> >> >
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> >
> >
> >
> > --
> > Erik Schnetter <schnetter at gmail.com>
> > http://www.perimeterinstitute.ca/personal/eschnetter/
> >
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-- 
Erik Schnetter <schnetter at gmail.com>
http://www.perimeterinstitute.ca/personal/eschnetter/
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