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@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@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@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@gmail.com>

>> wrote:

>> >

>> >

>> > On Tuesday, November 10, 2015, Erik Schnetter <schnetter@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@gmail.com>

>> >> http://www.perimeterinstitute.ca/personal/eschnetter/

>> >

>> >

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>

>

>

> --

> Erik Schnetter <schnetter@gmail.com>

> http://www.perimeterinstitute.ca/personal/eschnetter/

>

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