Question

我正在使用python matplotlib从温度数据的2D数组（存储在NetCDF文件中）生成等高线图，我有兴趣将轮廓多边形和/或线导出为geojson格式，以便我可以使用它们在matplotlib之外。我已经发现“pyplot.contourf”函数返回一个“QuadContourSet”对象，该对象具有包含轮廓坐标的“collections”属性：

contourSet = plt.contourf(data, levels)
collections = contourSet.collections

有没有人知道matplotlib是否有办法将“集合”中的坐标导出为各种格式，特别是geojson？我搜索了matplotlib文档和网页，但没有提出任何明显的内容。

谢谢！

Answer 1

geojsoncontour是一个Python模块，可将matplotlib等高线转换为geojson。

它使用以下简化但完整的方法将matplotlib轮廓转换为geojson：

import numpy
from matplotlib.colors import rgb2hex
import matplotlib.pyplot as plt
from geojson import Feature, LineString, FeatureCollection

grid_size = 1.0
latrange = numpy.arange(-90.0, 90.0, grid_size)
lonrange = numpy.arange(-180.0, 180.0, grid_size)
X, Y = numpy.meshgrid(lonrange, latrange)
Z = numpy.sqrt(X * X + Y * Y)

figure = plt.figure()
ax = figure.add_subplot(111)
contour = ax.contour(lonrange, latrange, Z, levels=numpy.linspace(start=0, stop=100, num=10), cmap=plt.cm.jet)

line_features = []
for collection in contour.collections:
    paths = collection.get_paths()
    color = collection.get_edgecolor()
    for path in paths:
        v = path.vertices
        coordinates = []
        for i in range(len(v)):
            lat = v[i][0]
            lon = v[i][1]
            coordinates.append((lat, lon))
        line = LineString(coordinates)
        properties = {
            "stroke-width": 3,
            "stroke": rgb2hex(color[0]),
        }
        line_features.append(Feature(geometry=line, properties=properties))

feature_collection = FeatureCollection(line_features)
geojson_dump = geojson.dumps(feature_collection, sort_keys=True)
with open('out.geojson', 'w') as fileout:
    fileout.write(geojson_dump)

Answer 2

确保导出所有轮廓的良好开端是在迭代get_paths个对象然后Collection to_polygons方法时使用Path方法得到numpy数组：

http://matplotlib.org/api/path_api.html?highlight=to_polygons#matplotlib.path.Path.to_polygons

然而，最终格式取决于你。

import matplotlib.pyplot as plt
cs = plt.contourf(data, levels)
for collection in cs.collections:
    for path in collection.get_paths():
        for polygon in path.to_polygons(): 
            print polygon.__class__
            print polygon

matplotlib等高线图geojson输出？

2 个答案: