[MOAB-dev] Geodesic mesh representation

[Paul Wilson]

Hi Chris,

MOAB should have no problem with this.  We use MOAB in this way 
frequently to represent curvilinear surfaces as sets of triangles, based 
on sets of vertices represented in 3D.

Paul


On 11/06/2013 06:39 PM, Chris Eldred wrote:
> This makes sense. I guess my concern was that I had coordinates in 3D
> and topology was 2D.
>
> So the mesh will have a dimension of 3 but the highest-dimensionality
> elements in it will be faces (2D)- and MOAB can deal with this?
>
> And yes my mesh looks basically identical to the MPAS mesh you attached.
>
> -Chris
>
> On Wed, Nov 6, 2013 at 5:32 PM, Iulian Grindeanu <iulian at mcs.anl.gov> wrote:
>> you maybe can follow this example:
>>
>> https://bitbucket.org/fathomteam/moab/src/bee2e77e416976393a63a221a814d85285403a7e/examples/old/FileRead.cpp?at=master
>>
>> It is a 2d mesh, but it reads from 2 files, one with coordinates position
>> and one with connectivity for triangles.
>>
>> You can create a mesh with just create_vertex() and create_element() methods
>> on moab::Interface
>>
>> ________________________________
>>
>> I have the mesh in a flat text file format- one file with vertex
>> coordinates, one file that lists the connectivity of faces to vertices
>> (ie for each face, what are the vertices that "bound" it).
>>
>> Topologically, the mesh is 2D since the highest dimensionality element
>> is a face (bounded by edges). However, the mesh represents a
>> discretization of the surface of a sphere, so vertex coordinates are
>> 3D (x,y,z). Since I am on the surface of a sphere of unit radius, I
>> could always go to a 2D coordinate representation in terms of angles
>> and just store the 3D coordinates as Tag values. Then everything would
>> be 2D (although the coordinates would be weird).
>>
>> It is unclear to me how to define a 3D mesh from this, since there
>> really are no cells (elements of dimension = 3) in the mesh.
>>
>> On Wed, Nov 6, 2013 at 4:44 PM, Iulian Grindeanu <iulian at mcs.anl.gov> wrote:
>>>
>>> ________________________________
>>>
>>> Dear Moab-Dev,
>>>
>>> I have a geodesic mesh (like MPAS or GCRM) and I was wondering what
>>> the best way to represent the mesh in MOAB was. It is topologically 2D
>>> but it is embedded in a 3D manifold (so vertex coordinates are x,y,z).
>>> I was thinking that I would treat the mesh as 2D, feed in "bogus"
>>> vertex coordinates and just use tags over the mesh elements to keep
>>> track of the actual mesh coordinates. This way, I keep the 2D
>>> topological structure (which is more important for my application
>>> anyways). Is this a good approach?
>>>
>>> Thanks,
>>> Chris Eldred
>>>
>>> --
>>> Chris Eldred
>>> DOE Computational Science Graduate Fellow
>>> Graduate Student, Atmospheric Science, Colorado State University
>>> B.S. Applied Computational Physics, Carnegie Mellon University, 2009
>>> chris.eldred at gmail.com / celdred at atmos.colostate.edu
>>>
>>> Probably I don't understand what you need :(
>>>
>>> What kind of format do you have ? netcdf? Is the mesh on a sphere /
>>> surface?
>>>
>>> The vertex coordinates are retrieved with "get_coords" methods, and set
>>> with
>>> set_coords methods, or use "coords_iterate" type methods in readUtil
>>> interface.
>>>
>>> Why not keep the full 3d mesh? what is so special about the 2d topological
>>> structure?
>>> Is it structured in any way? Can you use the MPAS reader or not?
>>>
>>> Iulian
>>>
>>
>>
>> --
>> Chris Eldred
>> DOE Computational Science Graduate Fellow
>> Graduate Student, Atmospheric Science, Colorado State University
>> B.S. Applied Computational Physics, Carnegie Mellon University, 2009
>> chris.eldred at gmail.com / celdred at atmos.colostate.edu
>>
>>
>
>

-- 
-- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ --
Paul Wilson ~ UW-Madison ~ 608-263-0807 ~ cal: http://bit.ly/pphw-cal
Professor, Engineering Physics. ~ http://cnerg.engr.wisc.edu
Faculty Director, Advanced Computing Infrastructure


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