Question about geometry options in WW 2.0 for ATS 1.6

[Chuyang Liu]

Hi there,

In Watershed Workflow v2.0, we can use various shapes—such as pentagons, quadrilaterals, and triangles—to discretize watersheds and river networks. I just wanted to double-check: is it possible to use other polygonal geometries, like hexagons, heptagons, or octagons, for building meshes compatible with ATS 1.6?

If so, I would greatly appreciate any suggestions or best practices for implementing such geometries. These alternative shapes might better suit the needs of my current modeling application. Additionally, if there are any potential issues to avoid when using non-standard element types, I would be glad to know about them as well.

Best,

Chuyang

[Rathore, Saubhagya]

Hi Chuyang,

 

It is not a problem for ATS—unstructured meshes with elements of arbitrary shape are supported. The main task is figuring out how to generate such meshes and export them in Exodus format. Watershed Workflow provides standardized workflow for stream-aligned mesh where catchments are discretized using TINs and river networks using quads and pentagons, but with some effort in understanding the meshing workflow you can incorporate other shapes as well, that too anywhere in the catchment.

 

Here’s what has worked for me in WW 1.6:

 

1. Create polygons for your “special” mesh cells.
2. Provide them as internal boundaries (list of shapely Polygons) during tessellation, with their centroids as hole points (list of shapely Points).
3. Identify the indices of vertices belonging to your “special” cells in the resulting TIN mesh, then define topology/connectivity for these cells as special_conns.
4. Append special_conns to TIN_conns, and create the m2 object using vertices from triangulation and TIN_conns + special_conns.

 

In WW 2.0, the tessellation function directly yields the m2 mesh, so you can’t manipulate conns externally. But instead of relying on the high-level function, you can always call the lower-level routines and construct the m2 object yourself in a notebook.

 

There may be other approaches as well—for instance see this paper using polygons of various shapes for representing artic tundra landscape.

https://link.springer.com/article/10.1007/s10596-017-9679-3

 

Thanks,

Saubhagya

 

From: ats-...@googlegroups.com <ats-...@googlegroups.com> on behalf of Chuyang Liu <CL...@lbl.gov>
Date: Wednesday, September 17, 2025 at 2:58 PM
To: Amanzi-ATS Users <ats-...@googlegroups.com>
Subject: [EXTERNAL] Question about geometry options in WW 2.0 for ATS 1.6

Hi there, In Watershed Workflow v2. 0, we can use various shapes—such as pentagons, quadrilaterals, and triangles—to discretize watersheds and river networks. I just wanted to double-check: is it possible to use other polygonal geometries, like

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