使用 RegularGridInterpolator 时，如何仅在边界外使用最近邻插值

Question

使用 RegularGridInterpolator 获取输入数据外壳（边界）之外的值，可以在外推值或固定值之间进行选择。如何在船体内部进行线性插值，在船体外部进行最近邻插值？

Answer 1

下面的class使用了两个插值器。第一个将船体外的所有值设置为 np.nan。第二个插值器仅对那些 nan 值进行最近邻插值。

class RegularGridInterpolatorNNextrapol:
    def __init__( self, points, values, method='linear' ):
        self.interp = RegularGridInterpolator(points, values, method=method,
                                              bounds_error=False, fill_value=np.nan)
        self.nearest = RegularGridInterpolator(points, values, method='nearest',
                                           bounds_error=False, fill_value=None)

    def __call__( self, xi ):
        vals = self.interp( xi )
        idxs = np.isnan( vals )
        vals[idxs] = self.nearest( xi[idxs] )
        return vals

这是一个生成下图的示例：

x = np.linspace( -0.5, 0.5, 5 )
y = np.linspace( -0.5, 0.5, 5 )
X1, Y1 = np.meshgrid(x, y)
z = np.hypot(X1, Y1)

interp = RegularGridInterpolatorNNextrapol((x,y), z)

X = np.linspace(min(x)-0.2, max(x)+0.2,40)
Y = np.linspace(min(y)-0.2, max(y)+0.2,40)
X, Y = np.meshgrid(X, Y)  # 2D grid for interpolation

pts = np.column_stack((X.flatten(),Y.flatten()))
Z = interp( pts )

plt.pcolormesh(X, Y, Z.reshape(X.shape), shading='auto')
plt.plot(X1, Y1, "ok" )
plt.legend()
plt.colorbar()
plt.axis("equal")
plt.show()

使用 RegularGridInterpolator 时，如何仅在边界外使用最近邻插值

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