不幸的是,matplotlib没有提供类似Matlab中的demcmap
功能。可能在Python basemap
包中有一些内置功能,我不知道。
因此,我们可以在matplotlib自带选项中使用子类Normalize
,构建围绕颜色图谱中间点的颜色规范化。这种技术可以在StackOverflow上的另一个问题中找到,并根据特定需求进行调整,即设置一个sealevel
(可能最好选择为0
)以及颜色图谱col_val
(介于0和1之间)应与该海平面相对应的值。在地形图的情况下,看起来0.22
,对应于蓝绿色,可能是一个不错的选择。
然后将Normalize实例作为imshow
的参数给出。结果可以在下面的图片的第一行中看到。
由于海平面周围的平滑过渡,0
附近的值呈现为蓝绿色,使得很难区分陆地和海洋。
因此,我们可以稍微改变地形图,并剪切掉那些颜色,从而更好地显示海岸线。这是通过组合介于0和0.17以及0.25到1之间的地图的两个部分来完成的,因此剪切了其中的一部分。
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.colors
class FixPointNormalize(matplotlib.colors.Normalize):
"""
Inspired by https://dev59.com/b2Ij5IYBdhLWcg3wilrB
Subclassing Normalize to obtain a colormap with a fixpoint
somewhere in the middle of the colormap.
This may be useful for a `terrain` map, to set the "sea level"
to a color in the blue/turquise range.
"""
def __init__(self, vmin=None, vmax=None, sealevel=0, col_val = 0.21875, clip=False):
self.sealevel = sealevel
self.col_val = col_val
matplotlib.colors.Normalize.__init__(self, vmin, vmax, clip)
def __call__(self, value, clip=None):
x, y = [self.vmin, self.sealevel, self.vmax], [0, self.col_val, 1]
return np.ma.masked_array(np.interp(value, x, y))
colors_undersea = plt.cm.terrain(np.linspace(0, 0.17, 56))
colors_land = plt.cm.terrain(np.linspace(0.25, 1, 200))
colors = np.vstack((colors_undersea, colors_land))
cut_terrain_map = matplotlib.colors.LinearSegmentedColormap.from_list('cut_terrain', colors)
data = np.linspace(-1000,2400,15**2).reshape((15,15))
fig, ax = plt.subplots(nrows = 2, ncols=3, figsize=(11,6) )
plt.subplots_adjust(left=0.08, right=0.95, bottom=0.05, top=0.92, hspace = 0.28, wspace = 0.15)
plt.figtext(.5, 0.95, "Using 'terrain' and FixedPointNormalize", ha="center", size=14)
norm = FixPointNormalize(sealevel=0, vmax=3400)
im = ax[0,0].imshow(data+1000, norm=norm, cmap=plt.cm.terrain)
fig.colorbar(im, ax=ax[0,0])
norm2 = FixPointNormalize(sealevel=0, vmax=3400)
im2 = ax[0,1].imshow(data, norm=norm2, cmap=plt.cm.terrain)
fig.colorbar(im2, ax=ax[0,1])
norm3 = FixPointNormalize(sealevel=0, vmax=0)
im3 = ax[0,2].imshow(data-2400.1, norm=norm3, cmap=plt.cm.terrain)
fig.colorbar(im3, ax=ax[0,2])
plt.figtext(.5, 0.46, "Using custom cut map and FixedPointNormalize (adding hard edge between land and sea)", ha="center", size=14)
norm4 = FixPointNormalize(sealevel=0, vmax=3400)
im4 = ax[1,0].imshow(data+1000, norm=norm4, cmap=cut_terrain_map)
fig.colorbar(im4, ax=ax[1,0])
norm5 = FixPointNormalize(sealevel=0, vmax=3400)
im5 = ax[1,1].imshow(data, norm=norm5, cmap=cut_terrain_map)
cbar = fig.colorbar(im5, ax=ax[1,1])
norm6 = FixPointNormalize(sealevel=0, vmax=0)
im6 = ax[1,2].imshow(data-2400.1, norm=norm6, cmap=cut_terrain_map)
fig.colorbar(im6, ax=ax[1,2])
for i, name in enumerate(["land only", "coast line", "sea only"]):
for j in range(2):
ax[j,i].text(0.96,0.96,name, ha="right", va="top", transform=ax[j,i].transAxes, color="w" )
plt.show()
![enter image description here](https://istack.dev59.com/nchSZ.webp)