# Mesh connectivity for volume coupling **URL:** \ **Category:** Using preCICE\ **Tags:** volume-coupling\ **Created:** [September 4, 2025, 6:56pm UTC](https://precice.discourse.group/t/mesh-connectivity-for-volume-coupling/2614 "2025-09-04T18:56:37Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Ray\_Scarr](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/ray_scarr/32/980_2.png) [@Ray\_Scarr](https://precice.discourse.group/u/Ray_Scarr)\ **Post date:** [September 4, 2025, 6:56pm UTC](https://precice.discourse.group/t/mesh-connectivity-for-volume-coupling/2614/1 "2025-09-04T18:56:37Z")
Building on [this topic](https://precice.discourse.group/t/volume-coupling-to-particle-tracker/2586/4), I want to check my understanding of when connectivity information is required for volume coupling. Suppose I have a hexahedral mesh for my fluid solver. I would expect that I could pass the cell centroids to preCICE as a point cloud, with which I could do [just-in-time data mapping](https://precice.org/couple-your-code-just-in-time-mapping.html) with any of the RBF interpolation methods, or just nearest neighbor. I would only need to split the cells into tetrahedra if I wanted to use nearest-projection. In other words, the information my fluid solver needs to pass to preCICE for volume coupling is analogous to what it sends for surface coupling. Is this correct? Is there any reason to prefer nearest-projection or RBFs for coupling a fluid solver to a particle solver? ---
**Author:** ![fsimonis](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/fsimonis/32/6_2.png) [@fsimonis](https://precice.discourse.group/u/fsimonis)\ **Post date:** [September 9, 2025, 11:52am UTC](https://precice.discourse.group/t/mesh-connectivity-for-volume-coupling/2614/2 "2025-09-09T11:52:27Z")
> [@Ray\_Scarr](#): > > I want to check my understanding of when connectivity information is required for volume coupling. Connectivity information for volume coupling is only required for mappings: - both `to` and `from` meshes of a mapping using `constraint="scaled-consistent-volume"` - `to` mesh of a `linear-cell-interpolaiton` mapping with `constraint="conservative"` - `from` mesh of a `linear-cell-interpolaiton` mapping with `constraint="consistent"` It’s also used by ``. > [@Ray\_Scarr](#): > > I would only need to split the cells into tetrahedra if I wanted to use nearest-projection. Only if your mapping constrain requires it. As you do volume coupling, `linear-cell-interpolation` is likely what you want to use. `nearest-projection` is for surface coupling. > [@Ray\_Scarr](#): > > In other words, the information my fluid solver needs to pass to preCICE for volume coupling is analogous to what it sends for surface coupling. Is this correct? Correct > [@Ray\_Scarr](#): > > Is there any reason to prefer nearest-projection or RBFs for coupling a fluid solver to a particle solver? The linear-cell-interpolation mapping can be much faster and easier to debug than an RBF mappings. @DavidSCN and @r_walloner have more experience with this though. ---
**Author:** ![r\_walloner](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/r_walloner/32/3028_2.png) [@r\_walloner](https://precice.discourse.group/u/r_walloner)\ **Post date:** [September 9, 2025, 12:29pm UTC](https://precice.discourse.group/t/mesh-connectivity-for-volume-coupling/2614/3 "2025-09-09T12:29:41Z")
At the moment, just-in-time mapping only supports RBF and NN anyway. As @fsimonis already mentioned, both of these do not require connectivity information. So if you want/need to use just-in-time mapping, that would probably be the limiting factor. As for preferring RBF over NN, in my experience RBF can yield a more stable coupling. When using NN for mapping fluid velocities to the particles, I experienced more solver crashes, especially at larger time step sizes. ---
**Author:** ![Ray\_Scarr](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/ray_scarr/32/980_2.png) [@Ray\_Scarr](https://precice.discourse.group/u/Ray_Scarr)\ **Post date:** [September 9, 2025, 3:40pm UTC](https://precice.discourse.group/t/mesh-connectivity-for-volume-coupling/2614/4 "2025-09-09T15:40:46Z")
Thanks @fsimonis and @r_walloner, this clarifies much and saves me a lot of work. ---
**Author:** ![fsimonis](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/fsimonis/32/6_2.png) [@fsimonis](https://precice.discourse.group/u/fsimonis)\ **Post date:** [September 26, 2025, 9:55am UTC](https://precice.discourse.group/t/mesh-connectivity-for-volume-coupling/2614/5 "2025-09-26T09:55:49Z")