Rust version of SOLWEIG

[songololo]

@biglimp This repo sub-classes the solweig_runner classes to add Rust version of SOLWEIG.

The only change is that this version swaps-in `solweig.py. It is similar to existing solweig calc scripts but swaps-in Rust functions:

• Shadows
• GVF
• Anisotropic
• L veg
• K veg

These functions were identified through performance profiling and appear to work as intended per test_rustalgos.py

Demo here: Athens-demo.py

Individually these functions run between 3 - 20x faster with overall speedup of around 5x for the Athens demo. Larger rasters or more cores probably more.

[biglimp]

Nice! We are also working on implementation of GPU-calculation for the shadow casting algorithms. I wonder if a combination of rust and GPU is possible and if so, what the performance would be like...

[paolodep36]

what about this? https://github.com/xiaojianggis/gpusvf?tab=readme-ov-file. I am also wondering if numba could be another option. what you think?

[biglimp]

what about this? https://github.com/xiaojianggis/gpusvf?tab=readme-ov-file. I am also wondering if numba could be another option. what you think?

We are working on a gpu-version solweig. Should be available this autumn. We have tried numba implementation. The decrease in computation time was not great.

[songololo]

Nice! We are also working on implementation of GPU-calculation for the shadow casting algorithms. I wonder if a combination of rust and GPU is possible and if so, what the performance would be like...

@biglimp as an experiment I added a version of GPU shadowing to the rust branch. For the test dataset it is about 30x faster for shadowing calls but the speedup will vary widely.

PS - full disclosure the GPU version was mostly "vibe coded" from the rust version but it seems to be passing the tests I was using for the rust code.

[songololo]

Another update that larger files sometimes run out of RAM or GPU buffers so a new tiling workflow has been added as a branch in umep-core and is now the version that umepr (rust) is based on

[biglimp]

Just remember when you tile your data that you need an overlap between tiles. See e.g. this publication: Lindberg et al. 2025

[songololo]

Thanks @biglimp. Yes, this is what it does. It will add a buffer dynamically based on shadow length and then it will trim back the buffers before welding the tile together.

[songololo]

@biglimp a heads up that I've just merged a new implementation of the Rust version into the main branch (replacing the original UMEP Rust version).

This version has a full working standalone Python implementation in parallel with QGIS support and a working experimental plugin for QGIS version 4.

The purpose of this prototype is to test that we can get Rust and GPU and tiling support all working from the GDAL ecosystem within QGIS. So far it seems to work as intended, but we could do with some testing and feedback from anyone who's able to.

[biglimp]

Sounds great! We just need to specify version, as we constantly update solweig and a new version is coming out soon.

Also, we have other models and tools that probably would benefit from Rust and GPU, both the shadow casting tool and the Solar radiation tool (SEBE). They are all using the same type of shadow casting algorithms and in some cases even the same function. Would it be easy to add this functionality throughout the UMEP ecosystem?

Did you see the work from the US? Is your GPU-code derived from this or do you have your own? https://joss.theoj.org/papers/10.21105/joss.09535

@nilswallenberg, interesting implementation of both rust and gpu by @songololo

[songololo]

Thanks for the link. This version uses a different implementation and grew out of the work from last year's experiment. I'm trying to keep everything bundled into the Rust binary so that it is easy to install from QGIS 4 or from Python.

Happy to see how we can make this available for the other tools.

We can update the algorithm to match your latest versions, so if you let me know when new versions are released, I can incorporate those into this codebase.