# 大型网格正交化

[返回示例目录](index.md)

以下保留原笔记本的代码和已保存输出；转换过程中未重新执行代码。

本示例演示如何加载大型二维网格并进行正交化。首先导入所需的库。这里还使用 UGrid 库正确加载二维网格。

```python
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
from meshkernel import (
    GeometryList,
    MeshKernel,
    OrthogonalizationParameters,
    ProjectionType,
    Mesh2d,
)
from ugrid import UGrid, UGridMesh2D
```

定义正交性阈值和文件名。

```python
orthogonality_criteria = 0.3
input_file = "./Michigan_Huron_ORTHO_mc025_mn5_net.nc"
output_file = "./Michigan_Huron_orthogonality_issues.xyz"
```

读取网格几何数据。

```python
with UGrid(input_file, "r") as ug:
    num_mesh2d_topologies = ug.mesh2d_get_num_topologies()
    mesh2d_ugrid = ug.mesh2d_get(num_mesh2d_topologies - 1)
```

根据节点和边创建 `meshkernel` 的二维网格。

```python
mesh2d_mk = Mesh2d()
mesh2d_mk.node_x = mesh2d_ugrid.node_x
mesh2d_mk.node_y = mesh2d_ugrid.node_y
mesh2d_mk.edge_nodes = mesh2d_ugrid.edge_nodes
```

创建 `MeshKernel` 实例。

```python
mk = MeshKernel(ProjectionType.SPHERICAL)
```

设置网格，此调用计算开销较大。

```python
mk.mesh2d_set(mesh2d_mk)
```

获取网格。

```python
mesh2d_output = mk.mesh2d_get()
```

```python
fig, ax = plt.subplots()
mesh2d_output.plot_edges(ax, color="black")
```

![单元格 15 的绘图输出](images/08_mesh2d_orthogonalization_15_0.png)

查询正交性，此调用计算开销较大。

```python
orthogonality = mk.mesh2d_get_orthogonality().values
```

提取正交性指标值高于 `orthogonality_criteria` 的边。

```python
criteria_indices = np.where(orthogonality > orthogonality_criteria)[0]
```

将提取的边保存到文件。

```python
xyz_df = pd.DataFrame([])
xyz_df["edge_x"] = mesh2d_output.edge_x[criteria_indices]
xyz_df["edge_y"] = mesh2d_output.edge_y[criteria_indices]
xyz_df["orthogonality"] = orthogonality[criteria_indices]
xyz_df.to_csv(output_file, index=False, header=False, sep=" ")
```

## 执行正交化

```python
selecting_polygon = GeometryList(
    np.empty(0, dtype=np.double), np.empty(0, dtype=np.double)
)
land_boundaries = GeometryList(
    np.empty(0, dtype=np.double), np.empty(0, dtype=np.double)
)
```

```python
mk.mesh2d_compute_orthogonalization(
    project_to_land_boundary_option=0,
    orthogonalization_parameters=OrthogonalizationParameters(outer_iterations=1),
    selecting_polygon=selecting_polygon,
    land_boundaries=land_boundaries,
)
```

```python
mesh2d_output = mk.mesh2d_get()
```

```python
fig, ax = plt.subplots()
mesh2d_output.plot_edges(ax, color="black")
```

![单元格 26 的绘图输出](images/08_mesh2d_orthogonalization_26_0.png)