In [2]:
import fiona
c = fiona.open('/data/gdata/prov_capital.shp')
hits = list(c.items(bbox=(-5.0, 55.0, 0.0, 60.0)))
len(hits)
Out[2]:
0
迭代器与切割参数itertools.islice 的 stop 或 start, stop[, step] 的功能相同。要想查找迭代器的前两个参数，暂停即可。
In [3]:
hits = c.items(2, bbox=(-5.0, 55.0, 0.0, 60.0))
len(list(hits))
Out[3]:
0
要想得到迭代器第三到第五个参数，启动和停止即可。
In [4]:
hits = c.items(2, 5, bbox=(-5.0, 55.0, 0.0, 60.0))
len(list(hits))
Out[4]:
0
要想过滤属性值，可使用Python的内置 :py:func:filter 和:py:keyword:lambda函数 ，或者你也可以用单一属性的过滤功能，返回值为 True or False 。
In [5]:
def pass_positive_area(rec):
return rec['properties'].get('AREA', 0.0)>0.0
In [6]:
c = fiona.open('/data/gdata/prov_capital.shp')
hits = filter(pass_positive_area, c)
len(list(hits))
Out[6]:
0
In [7]:
import subprocess
import os
if not os.path.exists('/tmp/data'):
os.mkdir('/tmp/data')
cmd1 = 'ogr2ogr /tmp/data/ /data/gdata/GSHHS_c.shp GSHHS_c -nln foo'
cmd2 = 'ogr2ogr /tmp/data/ /data/gdata/GSHHS_c.shp GSHHS_c -nln bar'
subprocess.call(cmd1, shell=True)
subprocess.call(cmd2, shell=True)
Warning 1: Value 50654050.694499999 of field area of feature 1765 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 50654050.694499999 of field area of feature 1766 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 29220969.727000002 of field area of feature 1767 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 20154740.09 of field area of feature 1768 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 17534164.066799998 of field area of feature 1769 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 13919140.565400001 of field area of feature 3501 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 50654050.694499999 of field area of feature 1765 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 50654050.694499999 of field area of feature 1766 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 29220969.727000002 of field area of feature 1767 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 20154740.09 of field area of feature 1768 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 17534164.066799998 of field area of feature 1769 not successfully written. Possibly due to too larger number with respect to field width Warning 1: Value 13919140.565400001 of field area of feature 3501 not successfully written. Possibly due to too larger number with respect to field width
Out[7]:
0
一个数据源层可以用函数fiona.listlayers 列一下，写法是 listlayers()。在 Shapefile格式的情况下，层的名称需匹配文件库的名称。
In [8]:
import fiona
fiona.listlayers('/data/gdata')
Out[8]:
['GSHHS_c', 'GSHHS_h', 'GSHHS_l_L1', 'county_popu', 'hyd2_4l', 'prov_capital', 'region_popu', 'region_popu2', 'shape_towns', 'spatial_filter', 'world_pt', 'world_spatial_filter']
不像OGR，Fiona没有层与数据源的分类。要想访问层，需用数据源路径打开一个集，并用 layer 来指定该层。
In [9]:
import pprint
datasrc_path = '/data/gdata'
for name in fiona.listlayers(datasrc_path):
with fiona.open(datasrc_path, layer=name) as c:
pprint.pprint(c.schema)
{'geometry': 'Polygon',
'properties': {'Shape_Area': 'float:19.11',
'Shape_Leng': 'float:19.11',
'area': 'float:19.11',
'id': 'str:80',
'level': 'int:10',
'parent_id': 'int:10',
'sibling_id': 'int:10',
'source': 'str:80'}}
{'geometry': 'Polygon',
'properties': {'Shape_Area': 'float:19.11',
'Shape_Leng': 'float:19.11',
'area': 'float:19.11',
'id': 'str:80',
'level': 'int:10',
'parent_id': 'int:10',
'sibling_id': 'int:10',
'source': 'str:80'}}
{'geometry': 'Polygon',
'properties': {'area': 'float:24.15',
'id': 'str:80',
'level': 'int:10',
'parent_id': 'int:10',
'sibling_id': 'int:10',
'source': 'str:80'}}
{'geometry': 'Polygon',
'properties': {'AREA': 'float:13.11',
'NAME': 'str:60',
'PAC': 'int:10',
'POPU': 'float:13.11',
'Shape_Area': 'float:19.11',
'Shape_Leng': 'float:19.11'}}
{'geometry': 'LineString',
'properties': {'FNODE_': 'int:11',
'GBCODE': 'int32:6',
'HYD2_4M_': 'int:11',
'HYD2_4M_ID': 'int:11',
'LENGTH': 'float:12.3',
'LEVEL_LAKE': 'int32:1',
'LEVEL_RIVE': 'int32:1',
'LPOLY_': 'int:11',
'NAME': 'str:60',
'RPOLY_': 'int:11',
'TNODE_': 'int:11'}}
{'geometry': 'Point',
'properties': {'lat': 'float:13.11', 'lon': 'float:13.11', 'name': 'str:100'}}
{'geometry': 'Polygon',
'properties': {'code2': 'int32:5',
'code4': 'int32:5',
'name': 'str:50',
'pname': 'str:50',
'popu': 'float:13.11'}}
{'geometry': 'Polygon',
'properties': {'code2': 'int32:5',
'code4': 'int32:5',
'name': 'str:50',
'pname': 'str:50',
'popu': 'float:13.11'}}
{'geometry': 'Point',
'properties': {'County': 'int32:1',
'LocalCounc': 'int32:1',
'Name': 'str:62',
'PK_UID': 'int32:4',
'Peoples': 'int32:7',
'Region': 'int32:1'}}
{'geometry': 'Polygon', 'properties': {'FID': 'int:11'}}
{'geometry': 'Point',
'properties': {'AREA': 'float:17.2',
'CAT': 'int:16',
'CNTRY_NAME': 'str:80',
'FIPS_CNTRY': 'str:80',
'ORIG_FID': 'int:10',
'POP_CNTRY': 'float:17.2'}}
{'geometry': 'Polygon',
'properties': {'Shape_Area': 'float:19.11',
'Shape_Leng': 'float:19.11',
'area': 'float:19.11',
'id': 'str:80',
'level': 'int:10',
'parent_id': 'int:10',
'sibling_id': 'int:10',
'source': 'str:80'}}
原版本中图层还可以由索引来指定。现在似乎不行了。
In [13]:
# for i, name in enumerate(fiona.listlayers(datasrc_path)):
# print(i,name)
# with fiona.open(datasrc_path, layer=i) as c:
# print(len(c))
0 GSHHS_c
--------------------------------------------------------------------------- ValueError Traceback (most recent call last) Cell In[13], line 3 1 for i, name in enumerate(fiona.listlayers(datasrc_path)): 2 print(i,name) ----> 3 with fiona.open(datasrc_path, layer=i) as c: 4 print(len(c)) File /opt/conda/lib/python3.12/site-packages/fiona/env.py:457, in ensure_env_with_credentials.<locals>.wrapper(*args, **kwds) 454 session = DummySession() 456 with env_ctor(session=session): --> 457 return f(*args, **kwds) File /opt/conda/lib/python3.12/site-packages/fiona/__init__.py:342, in open(fp, mode, driver, schema, crs, encoding, layer, vfs, enabled_drivers, crs_wkt, ignore_fields, ignore_geometry, include_fields, wkt_version, allow_unsupported_drivers, opener, **kwargs) 339 path = _parse_path(fp) 341 if mode in ("a", "r"): --> 342 colxn = Collection( 343 path, 344 mode, 345 driver=driver, 346 encoding=encoding, 347 layer=layer, 348 ignore_fields=ignore_fields, 349 include_fields=include_fields, 350 ignore_geometry=ignore_geometry, 351 wkt_version=wkt_version, 352 enabled_drivers=enabled_drivers, 353 allow_unsupported_drivers=allow_unsupported_drivers, 354 **kwargs 355 ) 356 elif mode == "w": 357 colxn = Collection( 358 path, 359 mode, (...) 372 **kwargs 373 ) File /opt/conda/lib/python3.12/site-packages/fiona/collection.py:226, in Collection.__init__(self, path, mode, driver, schema, crs, encoding, layer, vsi, archive, enabled_drivers, crs_wkt, ignore_fields, ignore_geometry, include_fields, wkt_version, allow_unsupported_drivers, **kwargs) 224 if self.mode == "r": 225 self.session = Session() --> 226 self.session.start(self, **kwargs) 227 elif self.mode in ("a", "w"): 228 self.session = WritingSession() File fiona/ogrext.pyx:887, in fiona.ogrext.Session.start() ValueError: Null layer: <closed Collection '/data/gdata:gdata', mode 'r' at 0x7f39c04d55e0> gdata
若没有指定层， fiona.open 会返回第一层的开放集 。
In [14]:
with fiona.open(datasrc_path) as c:
c.name == fiona.listlayers(datasrc_path)[0]
要打开一个只读的shapefile，最简单的方法就是 fiona.open 函数，可以把其文件名作为一个命名图层的数据源。
如：
fiona.open('/tmp/foo.shp', 'r', layer='foo')在实践中，依靠隐含的第一层和默认 'r' 模式是很实用的。
In [15]:
'wah' not in fiona.listlayers(datasrc_path)
Out[15]:
True
In [16]:
datasrc_path = '/tmp/data'
with fiona.open(datasrc_path, layer='bar') as c:
with fiona.open(datasrc_path, 'w', layer='wah', **c.meta) as d:
d.write(next(iter(c)))
fiona.listlayers(datasrc_path)
Out[16]:
['foo', 'bar', 'wah']
在 'w' 模式中，如果指定的话，会覆盖原有的层，就像是Python的open功能似的。
In [17]:
'wah' in fiona.listlayers(datasrc_path)
Out[17]:
True
In [18]:
with fiona.open(datasrc_path, layer='bar') as c:
with fiona.open(datasrc_path, 'w', layer='wah', **c.meta) as d:
pass