[MOAB-dev] Order of the nodes in get_connectivity

[Filipe Antônio Cumaru Silva Alves]

Hi Vijay,

> Are you asking specifically about how to look at the numbering for the
> nodes in each element type ?
I was wondering if get_connectivity returns the nodes ordered by some 
spacial criterion. For example, given a pyramid formed by the nodes with 
coordinates (x,y,z) below

[(0,1,0), (1,0,0), (1,1,0), (0,0,0), (0.5, 0.5, 1)]

Calling get_connectivity would return the corresponding EntityHandles of

[(0,0,0), (1,0,0), (0,1,0), (1,1,0), (0.5,0.5,1)]

in this order.

> Again, what element types are you interested in?

I'm interested in polyhedra in general. I noticed MOAB already has 
entity types for tetrahedra, hexahedra, pyramids and prisms, besides one 
for generic polyhedra.

> You can look at the methods exposed by verdict.h and use the area
> calculation method corresponding to your element.
Thanks, that slipped under the radar. It'll be very useful.


Once again, many thanks.

Filipe

On 22/09/2020 16:36, Vijay S. Mahadevan wrote:

> Hi Filipe,
>
> Are you asking specifically about how to look at the numbering for the
> nodes in each element type ? These are available in the CN (Canonical
> Numbering) class [1]. If you are looking at numbering for specific
> element types, you can look more closely at the mConnectivityMap
> declaration in [2].
>
>> 1. Is there a method from MOAB to calculate areas and volumes?
> There are examples that do this. Again, what element types are you
> interested in?
>
> You can look at the methods exposed by verdict.h and use the area
> calculation method corresponding to your element.
>
>> 2. How are the nodes ordered in the get_connectivity method?
> The ordering in the get_connectivity uses the internal MOAB numbering
> in the local space.
>
> Vijay
>
> [1] https://ftp.mcs.anl.gov/pub/fathom/moab-docs-develop/CN_8cpp.html
> [2] https://ftp.mcs.anl.gov/pub/fathom/moab-docs-develop/MBCNArrays_8hpp_source.html
>
> On Tue, Sep 22, 2020 at 1:44 PM Filipe Antônio Cumaru Silva Alves
> <facsa at cin.ufpe.br> wrote:
>> Hello,
>>
>> I'm developing a tool for multiscale mesh preprocessing using MOAB and
>> I'm currently working on a method to calculate areas and volumes for the
>> mesh elements. This task depends on the order of the nodes returned by
>> the get_connectivity method. However, I can't find any information in
>> the documentation on how the nodes are sorted other than the definition
>> (here
>> <https://ftp.mcs.anl.gov/pub/fathom/moab-docs-develop/classmoab_1_1ElementSequence.html#a918f9016130f7b0d7e3598dda2984430>)
>> and the implementation (here
>> <https://ftp.mcs.anl.gov/pub/fathom/moab-docs-develop/classmoab_1_1UnstructuredElemSeq.html#af0d6d48f8d60cd82a1a8abc3a7d433ca>).
>>
>> Thus, I have two questions:
>>
>>   1. Is there a method from MOAB to calculate areas and volumes?
>>   2. How are the nodes ordered in the get_connectivity method?
>>
>>
>> Many thanks,
>>
>> --
>> Filipe Antônio Cumaru Silva Alves
>>