geopandas.sjoin_nearest接受max_distance和distance_col参数。距离的单位是什么/我怎么解释?是学位吗?
https://geopandas.org/en/stable/docs/reference/api/geopandas.sjoin_nearest.html geopandas.sjoin_nearest
虽然geoandas提供了坐标系之间转换的实用程序(例如to_crs)，但大多数geoandas操作忽略了投影信息。空间操作，如距离、面积、缓冲区等，以几何图形的任何单位完成。如果几何图形的单位是米，这些就是米。如果它们以度为单位，它们就以度为单位。
例如，让我们看一下自然地球数据集。通过查看这些值，您可以看到几何列是经纬度坐标:
In [1]: import geopandas as gpd
In [2]: gdf = gpd.read_file(gpd.datasets.get_path('naturalearth_lowres'))
In [3]: gdf
Out[3]:
pop_est continent name iso_a3 gdp_md_est geometry
0 920938 Oceania Fiji FJI 8374.0 MULTIPOLYGON (((180.00000 -16.06713, 180.00000...
1 53950935 Africa Tanzania TZA 150600.0 POLYGON ((33.90371 -0.95000, 34.07262 -1.05982...
2 603253 Africa W. Sahara ESH 906.5 POLYGON ((-8.66559 27.65643, -8.66512 27.58948...
3 35623680 North America Canada CAN 1674000.0 MULTIPOLYGON (((-122.84000 49.00000, -122.9742...
4 326625791 North America United States of America USA 18560000.0 MULTIPOLYGON (((-122.84000 49.00000, -120.0000...
.. ... ... ... ... ... ...
172 7111024 Europe Serbia SRB 101800.0 POLYGON ((18.82982 45.90887, 18.82984 45.90888...
173 642550 Europe Montenegro MNE 10610.0 POLYGON ((20.07070 42.58863, 19.80161 42.50009...
174 1895250 Europe Kosovo -99 18490.0 POLYGON ((20.59025 41.85541, 20.52295 42.21787...
175 1218208 North America Trinidad and Tobago TTO 43570.0 POLYGON ((-61.68000 10.76000, -61.10500 10.890...
176 13026129 Africa S. Sudan SSD 20880.0 POLYGON ((30.83385 3.50917, 29.95350 4.17370, ...
[177 rows x 6 columns]
具体来说，它在WGS84(又名EPSG:4326)中。单位为度:
In [4]: gdf.crs
Out[4]:
<Geographic 2D CRS: EPSG:4326>
Name: WGS 84
Axis Info [ellipsoidal]:
- Lat[north]: Geodetic latitude (degree)
- Lon[east]: Geodetic longitude (degree)
Area of Use:
- name: World.
- bounds: (-180.0, -90.0, 180.0, 90.0)
Datum: World Geodetic System 1984 ensemble
- Ellipsoid: WGS 84
- Prime Meridian: Greenwich
如果我们调用area属性，geopandas将发出警告，但它仍然会为我们计算面积。地球的总面积为21497度^2，大约是180*360的1/3:
In [6]: gdf.area.sum()
<ipython-input-6-10238de14784>:1: UserWarning: Geometry is in a geographic CRS. Results from 'area' are likely incorrect. Use 'GeoSeries.to_crs()' to re-project geometries to a projected CRS before this operation.
gdf.area.sum()
Out[6]: 21496.990987992736
如果我们使用等面积投影，我们将得到更接近地球陆地面积的东西，单位是m^2:
In [10]: gdf.to_crs('+proj=cea').area.sum() / 1e3 / 1e3 / 1e6
Out[10]: 147.36326937311017