mbIntxCheck

Verify a precomputed mesh intersection against its source and target meshes. After a parallel run of mbtempest (or any other intersection generator) produces an intersection mesh, this tool checks that the per-element areas balance correctly between source / target / intersection.

For each source element, sum the areas of all intersection polygons that claim it as their source parent — that sum should equal the source element's own area, to within a configurable tolerance. Same check on the target side. Mismatches are written as element-level tags to per-side verification files.

Synopsis

mpiexec -n N  mbintx_check  -s <source.h5m>  -t <target.h5m>  -i <intx.h5m> \
                            -v <source_verif.h5m> -w <target_verif.h5m> \
                            [options]

Binary name on disk is mbintx_check.

Options

Flag	Default	Description
-s <file>, --source <file>	—	Source mesh (parent on one side of the intersection).
-t <file>, --target <file>	—	Target mesh (parent on the other side).
-i <file>, --intersection <file>	—	Precomputed intersection mesh. Each element carries srcParent / tgtParent tags pointing back into the source/target.
-v <file>, --verif_source <file>	—	Output: source mesh with per-cell area_error tag written.
-w <file>, --verif_target <file>	—	Output: target mesh with per-cell area_error tag written.
-m <eps>, --threshold_source <eps>	small	Pass/fail threshold for the per-cell source-area error.
-q <eps>, --threshold_target <eps>	small	Pass/fail threshold for the per-cell target-area error.
-p {0\|1}, --sphere <flag>	1	Mesh sits on a sphere (1) or in a plane (0); affects how areas are computed.
-n {0\|1}, --old_convention <flag>	0	Use the legacy parent tag names (pre-current convention). Set this if the intersection file was produced by an older mbtempest.

What it does

1. Reads the three meshes in parallel.
2. For each intersection element i:
   • Looks up its source parent s = srcParent[i] and target parent t = tgtParent[i].
   • Accumulates area(i) into the running totals src_sum[s] and tgt_sum[t].
3. After the gather, computes per-cell errors:

   src_error[s] = area(s) − src_sum[s]
   tgt_error[t] = area(t) − tgt_sum[t]

4. Writes the errors as element-level tags on the corresponding source / target mesh and saves them to the verification files.
5. Prints summary statistics (max error, number of cells above threshold) per side.

If the intersection is correct, both errors are zero to floating-point precision. Non-zero errors indicate missing or duplicated intersection polygons.

Example

After a parallel mbtempest run that produced intx.h5m:

mpiexec -n 4  mbintx_check \
  -s source.h5m  -t target.h5m  -i intx.h5m \
  -v source_verif.h5m  -w target_verif.h5m \
  -m 1e-10  -q 1e-10

Open source_verif.h5m and target_verif.h5m in ParaView/VisIt and color by the area_error tag to spot regions where the intersection is incomplete.

Sphere vs plane

The -p flag selects the geometric model:

• -p 1 (default): areas are computed as spherical-polygon areas on the unit sphere. Use for climate / atmosphere / ocean grids.
• -p 0: areas are computed as planar-polygon areas. Use for 2-D regional or Cartesian meshes.

See also

• `mbtempest` — generates the intersection meshes that mbIntxCheck verifies
• `compareMaps` — diff two remap weight files (different goal: matrix equivalence vs. area consistency)