Question

我正在尝试将GRASS GIS矢量层读入GeoPandas Dataframe。

由于我无法启用GRASS GIS see related issue

中的Fiona（只读）驱动程序，

我制作了一个“ hackish”方法（该方法有效），将GRASS GIS矢量层读入GeoPandas Dataframe：


import os
from osgeo import ogr
import pandas as pd
from shapely import wkt
import geopandas as gpd


def grass2gpd(layername, grassdb, location_name, mapset):
    datafile = os.path.join(GRASSDB, LOCATION_NAME, MAPSET, 'vector', layername, 'head')
    driver = ogr.GetDriverByName('GRASS')
    # here the data is read in readonly mode, but also the GDAL GRASS driver has no write capabilities
    # I am not sure at the end of the method on how to properly close the datasource (and, actually, if I have to ... )  
    dataSource = driver.Open(datafile, 0)     
    layer = dataSource.GetLayer() 
    srs = layer.GetSpatialRef().ExportToWkt()
    lyrDefn = layer.GetLayerDefn() 
    fieldnames = []
    for i in range( lyrDefn.GetFieldCount() ):  
        fieldnames.append(lyrDefn.GetFieldDefn(i).GetName() )
    # hack to avoid to call `layer.ResetReading()` and iterate again over the features
    #
    # I first build a list of dictionaries
    # each element of the list is of the form:
    # {geom: WKT_Geometry
    #  attr: {field_1: val, field_2: val, ..., field_N: val}}
    # So the attr key is a dictionary itself
    # the nested loop first get the feature then create a dictionary of attributes looping over the list of fields
    # 
    wktgeom = [{'geom':feature.GetGeometryRef().ExportToWkt(), 
                'attr':{i:feature.GetField(i) for i in fieldnames}} for feature in layer] 
    # At this point I should close or unlink the datasource, but I can't find the right method to do it
    #
    # Create a dataframe from the list of dictionaries
    #
    df = pd.DataFrame(wktgeom)
    # convert the WKT string to a shapely WKT object
    # concatenate a Geometry dataframe with an attribute dataframe 
    df_geom = pd.concat([df['geom'].apply(wkt.loads),  
                        pd.DataFrame(list(df['attr'].values))], 
                       axis=1, sort=False)
    # transform the pandas dataframe into a geopandas dataframe
    gdf = gpd.GeoDataFrame(df_geom, geometry='geom', crs=srs)
    return gdf

运行它，例如：


GRASSDB="/home/epinux/Data/grassdata"
LOCATION_NAME="lonlat"
MAPSET="PERMANENT"

layername="img_left_filteredBS"

gdf = grass2gpd(layername=layername, 
                grassdb=GRASSDB, 
                location_name=LOCATION_NAME, 
                 mapset=MAPSET)
type(gdf)

# returns
# geopandas.geodataframe.GeoDataFrame

该方法将返回一个geopandas.geodataframe.GeoDataFrame，如我所愿，但是...

我想知道是否存在直接传递到GeoPandas接口读取的OGR数据源GDAL-OGR Python的方法。如果没有，您是否有任何建议可以改进我提出的“骇人方法”？我在代码中添加了一些内联注释，试图解释我的担忧。

Answer 1

我刚收到Issue I opened on GitHub的回复，通过在OGR_GRASS中启用Fiona驱动程序解决了问题，以下代码可以正常工作：

import fiona
import geopandas as gpd

fiona.supported_drivers["OGR_GRASS"] = "r" 
gdf = gpd.read_file('/GRASSDB/LOCATION_NAME/MAPSET/vector/layername/head')

使用GeoPandas在Python中读取GRASS矢量数据源

1 个答案: