[MDAL-Developer] 3D Meshes

[Paul Harwood]

Re-opening this and adding back the wider group( I had not noticed that
they had dropped off).

The question is about saving 3D meshes with volumetric datasets. The
context is around creating a python interface and using it for 3D
volumetric data.

There are a number of questions coming out of this work - I will raise
individual issues and PRs where appropriate but I wanted to discuss the
issues wider:

1 There seems to be a general lack of drivers capable of writing any sort
of data - according to the flags and therefore also according to the C API
which checks the flags. UGRID, for instance, was mentioned but the Ugrid
driver capabilities do not include the ability to write ANY data. Is that
correct? It seems to contradict what has been said elsewhere.

There are three drivers that can write meshes (2DM, SELAFIN and UGRID). Of
these only one can write data - SELAFIN - and only on vertices. This is
very limited. Is it correct?

The flags also say that DataOnFace can be written by the TUFLOW FV driver
but that meshes cannot, and that data can be written by the DAT drivers.
But none of that helps with creating a new mesh with data of any type (let
alone 3D).

2 There are NO drivers that admit to the ability to write DataOnVolumes
datasets.

Is this true?

3 The C API MDAL_G_addDataset() method explicitly excludes (i.e. there is a
validation check to enforce the exclusion) creation of DataOnVolume
datasets. This does make the conversation earlier in the email chain about
how to create these datasets incorrect. Is there a reason for this
exclusion and is there a way around it.

Thanks for any pointers / comments

Paul

On Thu, 17 Jun 2021 at 10:22, Paul Harwood <runette at gmail.com> wrote:

> Ok, thanks. Got it now
>
> On Thu, 17 Jun 2021 at 10:20, Peter Petrik <
> peter.petrik at lutraconsulting.co.uk> wrote:
>
>> base net is same as 2D mesh, verticals are just datasets defined in
>> https://github.com/lutraconsulting/MDAL/blob/42eb61f880f99ca0aa89a72f5afc5193b2f061e2/mdal/api/mdal.h#L648
>>
>>
>>
>> On Thu, Jun 17, 2021 at 11:07 AM Paul Harwood <runette at gmail.com> wrote:
>>
>>> To be more precise - I can see how to add volume based datasets but not
>>> how to add the vertical structure - i.e. the number of volumes per face of
>>> the base net.
>>>
>>> On Thu, 17 Jun 2021 at 08:18, Paul Harwood <runette at gmail.com> wrote:
>>>
>>>> We probably need to change or clarify the README which says that 3D
>>>> data is not supported for UGRID. Does that column mean something else ?
>>>>
>>>> Is the support read-only? I cannot immediately see how to use the C API
>>>> to write a layered 3D mesh.
>>>>
>>>> On Thu, 17 Jun 2021 at 07:27, Peter Petrik <
>>>> peter.petrik at lutraconsulting.co.uk> wrote:
>>>>
>>>>>
>>>>> https://ugrid-conventions.github.io/ugrid-conventions/#3d-layered-mesh-topology
>>>>> is supported
>>>>>
>>>>> On Wed, Jun 16, 2021 at 8:38 PM Paul Harwood <runette at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Sorry - in that last email when I said "is UGRID unstructured 3d MESH
>>>>>> supported"? I meant "is UGRID LAYERED 3d mesh supported"!
>>>>>>
>>>>>> On Wed, 16 Jun 2021 at 19:35, Paul Harwood <runette at gmail.com> wrote:
>>>>>>
>>>>>>> Peter
>>>>>>>
>>>>>>> Can I just confirm. I look at the GH readme and it says that only
>>>>>>> XMDF supports 3d (i.e. I guess TUFLOW). There is an issue about UGRID that
>>>>>>> mentions a PR. Also the Readme says that XMDF support for 3D is read-only.
>>>>>>>
>>>>>>> Is UGRID Unstructured 3D mesh supported?
>>>>>>>
>>>>>>> Is any 3D RW?
>>>>>>>
>>>>>>> On Wed, 16 Jun 2021 at 14:59, Paul Harwood <runette at gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> That makes sense. Thanks. I think that ugrid is what I want
>>>>>>>>
>>>>>>>> On Wed, 16 Jun 2021, 14:45 Peter Petrik, <
>>>>>>>> peter.petrik at lutraconsulting.co.uk> wrote:
>>>>>>>>
>>>>>>>>> I think we only support TUFLOW 3d data and UGRID specification for
>>>>>>>>> 3D stuff, which limits your options quite a bit :)
>>>>>>>>>
>>>>>>>>> P.
>>>>>>>>>
>>>>>>>>> On Wed, Jun 16, 2021 at 3:28 PM Paul Harwood <runette at gmail.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Hi all
>>>>>>>>>>
>>>>>>>>>> I am thinking about voxel based 3D data in meshes.
>>>>>>>>>>
>>>>>>>>>> I am aware of this
>>>>>>>>>> https://github.com/qgis/QGIS-Enhancement-Proposals/issues/158
>>>>>>>>>>
>>>>>>>>>> The question I have is a simple one :
>>>>>>>>>>
>>>>>>>>>> Absent any other constraint, what would be the "best" format to
>>>>>>>>>> use to hold and transfer voxel based 3D mesh data?
>>>>>>>>>> _______________________________________________
>>>>>>>>>> MDAL-Developer mailing list
>>>>>>>>>> MDAL-Developer at lists.osgeo.org
>>>>>>>>>> https://lists.osgeo.org/mailman/listinfo/mdal-developer
>>>>>>>>>>
>>>>>>>>>
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