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Use the real mesh geometry for plain Elmer mesh grids - #193
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Plain --elmer-mesh grids (no DEM) put every column at lat 75, lon 320 (75 N 40 W), placeholder values from the initial implementation. Use the mesh cell centers instead, as the --netcdf-dem-mesh branch already did; both branches now share _set_cell_center_coordinates. Longitudes are now -180..180 instead of 0..360. Both give the same hour angle modulo 360 deg, so cos/sin(h) are unchanged; only the shading azimuth's h < 0 test differs, and Elmer grids cannot shade. On greenland_mesh_v0 (default 1-day January run) Tsurf changes by up to 0.06 K. The CI pseudo-coupling step is bit-identical because its surface energy balance comes from (fake) ICON-Land. Assisted-by: Claude Code:claude-opus-5-5
Plain --elmer-mesh grids (no DEM file) filled grid["z"] with random values between 0 and 100 m. Use the mean of the node z coordinates of each cell instead, which is where reader.py stores DEM elevations and what README.md describes for this input. A mesh without elevation data now gives 0 m everywhere. Assisted-by: Claude Code:claude-opus-5-5
Plain --elmer-mesh grids treated every column as flat. Use the plane through the nodes of each triangle instead. Its gradient in projected x/y is rotated to local east/north with the meridian convergence of the mesh CRS and scaled by the projection scale factor, since slope_x/slope_y are east/north gradients and EPSG:3413/3031 x/y are not. Mesh now keeps its CRS for this. slope_beta/slope_gamma use the same formulas as the MATLAB branch (arctan of the slope, slope_azimuth). A mesh without elevation data, such as greenland_mesh_v0 in CI, still gives exactly zero slopes. With elevation data, --couple-to-elmer-ice now aborts at startup in ElmerIce.validate_grid. Assisted-by: Claude Code:claude-opus-5-5
Elmer mesh grids now carry real slopes, which ElmerIce rejected since they cannot follow the surface elevation it sends back (no dhdx/dhdy yet). That turned every Elmer/Ice run on a mesh with elevation data into an AssertionError. Zero the slopes with a warning instead, which is what these runs used before the mesh slopes were introduced. Shading and 2-D elevation fields are still rejected. validate_grid is renamed to prepare_grid since it now modifies the grid. Assisted-by: Claude Code:claude-opus-5-5
Assisted-by: Claude Code:claude-opus-5-5
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Grids built from
--elmer-meshalone (no--netcdf-dem-mesh/--netcdf-dem-mesh-unstructured) filled the column geometry with placeholder values from the initial implementation: every column at 75 N 40 W (lon 320), a random elevation between 0 and 100 m, and flat surfaces. This PR replaces them with the geometry of the mesh, one commit each:_set_cell_center_coordinates). Longitudes are now -180..180, as for all other grid types. 320 and -40 give the same hour angle modulo 360 deg; only the shading azimuth testsh < 0, and Elmer grids cannot shade.reader.pywrites DEM elevations. A mesh without elevation data gives 0 m.slope_beta/slope_gammause the formulas of the MATLAB branch, moved unchanged into_slope_angles.Where results change, and where they do not
Measured with
--dump-reference --random-seed 0andtools/compare_snapshots.py, default run (1 Jan 1979, 8 x 3 h), per commit against its parent.--matlab-mesh,--netcdf-mesh--elmer-mesh+--netcdf-dem-mesh(-unstructured)--elmer-meshalone, mesh without elevation (greenland_mesh_v0)reader.py)greenland_mesh_v0,--couple-to-icon-atmo --couple-to-icon-land --couple-to-elmer-ice --fake-coupling)Notes:
ebm_*diagnostics there. A standalone--elmer-meshrun on the same mesh does change.--elmer-meshruns now carries the reallon/latandz.Behaviour with Elmer/Ice coupling
When coupled to Elmer/Ice (
--couple-to-elmer-ice), the columns stay flat and a warning is logged, since the slopes would not follow the surface elevation received from Elmer/Ice (it does not senddhdx/dhdyyet). Such runs therefore get the same flat columns as before.ElmerIce.validate_gridis renamed toElmerIce.prepare_gridbecause it now adapts the grid; shading and 2-D elevation fields are still rejected.Not covered
--netcdf-dem-mesh(-unstructured)branches still use flat slopes; their elevations are interpolated to cell centers only, so there are no node elevations to fit a plane through.slope_gammahas the wrong sign whereslope_y == 0exactly; this is pre-existing, moved unchanged, and fixed separately.Generated with Claude Code