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SCRIP 0/360 seam duplicates nodes, giving euler_characteristic = 1 on a closed sphere

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評価

難易度
3/5
見積もり時間
1〜2日
初心者へのやさしさ
72/100
issue の種類
バグ
明瞭さ
明確に書かれている
活発さ
活発
技術スタック
numpy, python
領域
backend, data

調査の方向性

Start by running the provided MCVE with the SCRIP fixtures under test/meshfiles/scrip and compare it with Grid.from_healpix(3). Trace the SCRIP reader reached through ux.open_grid to its coordinate deduplication logic. Done means 0/360 seam nodes are merged and both listed closed meshes report Euler characteristic 2 without breaking the HEALPix control.

索引モデルが issue の本文から書いたものです。

説明

Version

2026.9.0 (and main)

How did you install UXarray?

Source

What happened?

A closed global SCRIP mesh reports euler_characteristic = 1 instead of 2.

SCRIP files store corner longitudes in 0..360 and include both endpoints of the seam: outCSne8 has 30 corners at lon=0 and 30 at lon=360. Those are the same meridian, but the reader's dedup compares (lon, lat) pairs literally, so the seam gets two sets of nodes and the mesh is topologically split along it.

mesh duplicate node coords V E F χ
outCSne8 15 407 790 384 1
ne30pg2 119 21,727 43,326 21,600 1
HEALPix z3 (control) 0 770 1,536 768 2

The HEALPix control has no duplicates and gives the right answer, which locates the problem in the SCRIP path rather than in the Euler computation.

Both meshes are reported as closed: true, so a caller gets a closure verdict that disagrees with the characteristic printed beside it.

What did you expect to happen?

χ = 2 for a closed sphere, and nodes on the 0/360 seam merged.

Can you provide a MCVE to reproduce the bug?
import numpy as np, uxarray as ux

for name, path in [
    ("outCSne8", "test/meshfiles/scrip/outCSne8/outCSne8.nc"),
    ("ne30pg2", "test/meshfiles/scrip/ne30pg2/grid.nc"),
]:
    g = ux.open_grid(path)
    V, E, F = int(g.n_node), int(g.n_edge), int(g.n_face)
    nodes = np.stack([np.round(g.node_lon.values, 9),
                      np.round(g.node_lat.values, 9)], 1)
    dupes = V - len(np.unique(nodes, axis=0))
    print(f"{name}: V={V} E={E} F={F} chi={V-E+F} duplicate_nodes={dupes}")

g = ux.Grid.from_healpix(3)          # control: no duplicates
V, E, F = int(g.n_node), int(g.n_edge), int(g.n_face)
print(f"healpix3: V={V} E={E} F={F} chi={V-E+F}")
Note

Same class as #1692 (coincident nodes), but the trigger here is specifically the 0/360 seam in SCRIP rather than general coincidence, and it reproduces on the meshes already in test/meshfiles. Unchanged by #1775 — that PR swaps the dedup algorithm but compares the same (lon, lat) pairs, so it inherits the behaviour rather than causing it.

主要言語
Python
スター
230
フォーク
56
平均マージ
6日 3時間
マージ済み PR（30日）
12

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