"""**Vector Module**
.. tip:: Provides functionality for manipulation of vector data. The data can
be in-memory or file based.
Resources for understanding vector data formats and the OGR library:
Treatise on vector data model: http://www.esri.com/news/arcuser/0401/topo.html
OGR C++ reference: http://www.gdal.org/ogr
"""
__author__ = 'Ole Nielsen <ole.moller.nielsen@gmail.com>'
__revision__ = '$Format:%H$'
__date__ = '01/11/2010'
__license__ = "GPL"
__copyright__ = 'Copyright 2012, Australia Indonesia Facility for '
__copyright__ += 'Disaster Reduction'
import os
import sys
import numpy
import logging
import copy as copy_module
from osgeo import ogr, gdal
from safe.common.utilities import (verify,
ugettext as safe_tr)
from safe.common.exceptions import ReadLayerError, WriteLayerError
from safe.common.exceptions import GetDataError, InaSAFEError
from layer import Layer
from projection import Projection
from geometry import Polygon
from utilities import DRIVER_MAP, TYPE_MAP
from utilities import read_keywords
from utilities import write_keywords
from utilities import get_geometry_type
from utilities import is_sequence
from utilities import array2wkt, array2ring
from utilities import calculate_polygon_centroid
from utilities import points_along_line
from utilities import geometrytype2string
from utilities import get_ringdata
from utilities import rings_equal
LOGGER = logging.getLogger('InaSAFE')
_pseudo_inf = float(99999999)
[docs]class Vector(Layer):
"""Class for abstraction of vector data.
"""
def __init__(self, data=None, projection=None, geometry=None,
geometry_type=None, name=None, keywords=None,
style_info=None, sublayer=None):
"""Initialise object with either geometry or filename
Args:
* data: Can be either
* A filename of a vector file format known to GDAL.
* List of dictionaries of field names and attribute values
associated with each point coordinate.
* None
* projection: Geospatial reference in WKT format.
Only used if geometry is provided as a numeric array,
if None, WGS84 geographic is assumed.
* geometry: A list of either point coordinates or polygons/lines
(see note below).
* geometry_type: Desired interpretation of geometry.
Valid options are 'point', 'line', 'polygon' or
the ogr types: 1, 2, 3.
If None, a geometry_type will be inferred from the data.
* name: Optional name for layer. If None, basename is used.
* keywords: Optional dictionary with keywords that describe the
layer. When the layer is stored, these keywords will
be written into an associated file with extension
'.keywords'.
Keywords can for example be used to display text about the
layer in an application.
* style_info: Dictionary with information about how this layer
should be styled. See impact_functions/styles.py
for examples.
* sublayer: str Optional sublayer (band name in the case of raster,
table name in case of sqlite etc.) to load. Only applicable
to those dataformats supporting more than one layer in the
data file.
Returns:
* An instance of class Vector.
Raises:
* Propogates any exceptions encountered.
Notes:
If data is a filename, all other arguments are ignored
as they will be inferred from the file.
The geometry type will be inferred from the dimensions of geometry.
If each entry is one set of coordinates the type will be
ogr.wkbPoint,
if it is an array of coordinates the type will be ogr.wkbPolygon.
To cast array entries as lines set geometry_type explicitly to
'line' in the call to Vector. Otherwise, they will default to
polygons.
Each polygon or line feature take the form of an Nx2 array
representing vertices where line segments are joined.
If polygons have holes, their geometry must be passed in as a
list of polygon geometry objects
(as defined in module geometry.py)
"""
# Invoke common layer constructor
Layer.__init__(self,
name=name,
projection=projection,
keywords=keywords,
style_info=style_info,
sublayer=sublayer)
# Input checks
if data is None and geometry is None:
# Instantiate empty object
self.geometry_type = None
self.extent = [0, 0, 0, 0]
return
if isinstance(data, basestring):
self.read_from_file(data)
else:
# Assume that data is provided as sequences provided as
# arguments to the Vector constructor
# with extra keyword arguments supplying metadata
msg = 'Geometry must be specified'
verify(geometry is not None, msg)
msg = 'Geometry must be a sequence'
verify(is_sequence(geometry), msg)
if len(geometry) > 0 and isinstance(geometry[0], Polygon):
self.geometry_type = ogr.wkbPolygon
self.geometry = geometry
else:
self.geometry_type = get_geometry_type(geometry, geometry_type)
# Convert to objects if input is a list of simple arrays
if self.is_polygon_data:
self.geometry = [Polygon(outer_ring=x) for x in geometry]
else:
self.geometry = geometry
if data is None:
# Generate default attribute as OGR will do that anyway
# when writing
data = []
for i in range(len(geometry)):
data.append({'ID': i})
# Check data
self.data = data
if data is not None:
msg = 'Data must be a sequence'
verify(is_sequence(data), msg)
msg = ('The number of entries in geometry and data '
'must be the same')
verify(len(geometry) == len(data), msg)
# Establish extent
if len(geometry) == 0:
# Degenerate layer
self.extent = [0, 0, 0, 0]
return
# Compute bounding box for each geometry type
minx = miny = sys.maxint
maxx = maxy = -minx
if self.is_point_data:
A = numpy.array(self.get_geometry())
minx = min(A[:, 0])
maxx = max(A[:, 0])
miny = min(A[:, 1])
maxy = max(A[:, 1])
elif self.is_line_data:
for g in self.get_geometry():
A = numpy.array(g)
minx = min(minx, min(A[:, 0]))
maxx = max(maxx, max(A[:, 0]))
miny = min(miny, min(A[:, 1]))
maxy = max(maxy, max(A[:, 1]))
elif self.is_polygon_data:
# Do outer ring only
for g in self.get_geometry(as_geometry_objects=False):
A = numpy.array(g)
minx = min(minx, min(A[:, 0]))
maxx = max(maxx, max(A[:, 0]))
miny = min(miny, min(A[:, 1]))
maxy = max(maxy, max(A[:, 1]))
self.extent = [minx, maxx, miny, maxy]
def __str__(self):
"""Render as name, number of features, geometry type
"""
g_type_str = geometrytype2string(self.geometry_type)
return ('Vector data set: %s, %i features, geometry type '
'%s (%s)' % (self.name,
len(self),
str(self.geometry_type),
g_type_str))
def __len__(self):
"""Size of vector layer defined as number of features
"""
if hasattr(self, 'geometry') and self.geometry is not None:
return len(self.geometry)
else:
return 0
def __eq__(self, other, rtol=1.0e-5, atol=1.0e-8):
"""Override '==' to allow comparison with other vector objecs
Args:
* other: Vector instance to compare to
* rtol, atol: Relative and absolute tolerance.
See numpy.allclose for details
Note:
The algorithm will try to falsify every aspect of equality for the
two layers such as data, geometry, projection, keywords etc.
Only if none of them can be falsified will it return True.
"""
# Check type
if not isinstance(other, Vector):
msg = ('Vector instance cannot be compared to %s'
' as its type is %s ' % (str(other), type(other)))
raise TypeError(msg)
# Check keywords
if self.keywords != other.keywords:
return False
# Check number of features match
if len(self) != len(other):
return False
# Check projection
if self.projection != other.projection:
return False
# Check geometry type
if self.geometry_type != other.geometry_type:
return False
# Check geometry
if self.is_polygon_data:
geom0 = self.get_geometry(as_geometry_objects=True)
geom1 = other.get_geometry(as_geometry_objects=True)
else:
geom0 = self.get_geometry()
geom1 = other.get_geometry()
if len(geom0) != len(geom1):
return False
if self.is_point_data:
if not numpy.allclose(geom0, geom1,
rtol=rtol, atol=atol):
return False
elif self.is_line_data:
# Check vertices of each line
for i in range(len(geom0)):
if not rings_equal(geom0[i], geom1[i], rtol=rtol, atol=atol):
return False
elif self.is_polygon_data:
# Check vertices of outer and inner rings
for i in range(len(geom0)):
x = geom0[i].outer_ring
y = geom1[i].outer_ring
if not rings_equal(x, y, rtol=rtol, atol=atol):
return False
for j, ring0 in enumerate(geom0[i].inner_rings):
ring1 = geom1[i].inner_rings[j]
if not rings_equal(ring0, ring1, rtol=rtol, atol=atol):
return False
else:
msg = ('== not implemented for geometry type: %s'
% self.geometry_type)
raise InaSAFEError(msg)
# Check keys for attribute values
x = self.get_data()
y = other.get_data()
if x is None:
if y is not None:
return False
else:
for key in x[0]:
for i in range(len(y)):
if key not in y[i]:
return False
for key in y[0]:
for i in range(len(x)):
if key not in x[i]:
return False
# Check attribute values
for i, a in enumerate(x):
for key in a:
X = a[key]
Y = y[i][key]
if X != Y:
# Not obviously equal, try some special cases
try:
# Try numerical comparison with tolerances
res = numpy.allclose(X, Y,
rtol=rtol, atol=atol)
except (NotImplementedError, TypeError):
# E.g. '' (Not implemented)
# or None or {} (Type error)
pass
else:
if not res:
return False
# Finally cast as booleans.
# This will e.g. match False with None or ''
if not (bool(X) is bool(Y)):
return False
# Vector layers are identical up to the specified tolerance
return True
[docs] def read_from_file(self, filename):
"""Read and unpack vector data.
It is assumed that the file contains only one layer with the
pertinent features. Further it is assumed for the moment that
all geometries are points.
* A feature is a geometry and a set of attributes.
* A geometry refers to location and can be point, line, polygon or
combinations thereof.
* The attributes or obtained through GetField()
The full OGR architecture is documented at
* http://www.gdal.org/ogr/ogr_arch.html
* http://www.gdal.org/ogr/ogr_apitut.html
Examples are at
* danieljlewis.org/files/2010/09/basicpythonmap.pdf
* http://invisibleroads.com/tutorials/gdal-shapefile-points-save.html
* http://www.packtpub.com/article/geospatial-data-python-geometry
Limitation of the Shapefile are documented in
http://resources.esri.com/help/9.3/ArcGISDesktop/com/Gp_ToolRef/
geoprocessing_tool_reference/
geoprocessing_considerations_for_shapefile_output.htm
"""
basename = os.path.splitext(filename)[0]
# Look for any keywords
self.keywords = read_keywords(basename + '.keywords')
# FIXME (Ole): Should also look for style file to populate style_info
# Determine name
if 'title' in self.keywords:
title = self.keywords['title']
# Lookup internationalised title if available
title = safe_tr(title)
vectorname = title
else:
# Use basename without leading directories as name
vectorname = os.path.split(basename)[-1]
if self.name is None:
self.name = vectorname
self.filename = filename
self.geometry_type = None # In case there are no features
fid = ogr.Open(filename)
if fid is None:
msg = 'Could not open %s' % filename
raise ReadLayerError(msg)
# Assume that file contains all data in one layer
msg = 'Only one vector layer currently allowed'
if fid.GetLayerCount() > 1 and self.sublayer is None:
msg = ('WARNING: Number of layers in %s are %i. '
'Only the first layer will currently be '
'used. Specify sublayer when creating '
'the Vector if you wish to use a different layer.'
% (filename, fid.GetLayerCount()))
LOGGER.warn(msg)
# Why do we raise an exception if it is only a warning? TS
raise ReadLayerError(msg)
if self.sublayer is not None:
layer = fid.GetLayerByName(self.sublayer)
else:
layer = fid.GetLayerByIndex(0)
# Get spatial extent
self.extent = layer.GetExtent()
# Get projection
p = layer.GetSpatialRef()
self.projection = Projection(p)
layer.ResetReading()
# Extract coordinates and attributes for all features
geometry = []
data = []
# Use feature iterator
for feature in layer:
# Record coordinates ordered as Longitude, Latitude
G = feature.GetGeometryRef()
if G is None:
msg = ('Geometry was None in filename %s ' % filename)
raise ReadLayerError(msg)
else:
self.geometry_type = G.GetGeometryType()
if self.is_point_data:
geometry.append((G.GetX(), G.GetY()))
elif self.is_line_data:
ring = get_ringdata(G)
geometry.append(ring)
elif self.is_polygon_data:
# Get outer ring, then inner rings
# http://osgeo-org.1560.n6.nabble.com/
# gdal-dev-Polygon-topology-td3745761.html
number_of_rings = G.GetGeometryCount()
# Get outer ring
outer_ring = get_ringdata(G.GetGeometryRef(0))
# Get inner rings if any
inner_rings = []
if number_of_rings > 1:
for i in range(1, number_of_rings):
inner_ring = get_ringdata(G.GetGeometryRef(i))
inner_rings.append(inner_ring)
# Append Polygon instance to geometry list
geometry.append(Polygon(outer_ring=outer_ring,
inner_rings=inner_rings))
elif self.is_multi_polygon_data:
try:
G = ogr.ForceToPolygon(G)
# FIXME: reuse the code for polygon above
ring = G.GetGeometryRef(0)
M = ring.GetPointCount()
coordinates = []
for j in range(M):
coordinates.append((ring.GetX(j), ring.GetY(j)))
# Record entire polygon ring as an Mx2 numpy array
geometry.append(numpy.array(coordinates,
dtype='d',
copy=False))
# msg = ('Got geometry type Multipolygon (%s) for filename '
# '%s which is not yet supported. Only point, line '
# 'and polygon geometries are supported. However, '
# 'you can use QGIS functionality to convert '
# 'multipart vector data to singlepart (Vector -> '
# 'Geometry Tools -> Multipart to Singleparts and '
# 'use the resulting dataset.'
# % (ogr.wkbMultiPolygon, filename))
except:
msg = ('Got geometry type multipolygon (%s) when read '
'%s and failed to ForceToPolygon')
raise ReadLayerError(msg)
# # FIXME: Unpact multiple polygons to simple polygons
# # For hints on how to unpack see
#http://osgeo-org.1803224.n2.nabble.com/
#gdal-dev-Shapefile-Multipolygon-with-interior-rings-td5391090.html
#http://osdir.com/ml/gdal-development-gis-osgeo/2010-12/msg00107.html
# ring = G.GetGeometryRef(0)
# M = ring.GetPointCount()
# coordinates = []
# for j in range(M):
# coordinates.append((ring.GetX(j), ring.GetY(j)))
# # Record entire polygon ring as an Mx2 numpy array
# geometry.append(numpy.array(coordinates,
# dtype='d',
# copy=False))
else:
msg = ('Only point, line and polygon geometries are '
'supported. '
'Geometry type in filename %s '
'was %s.' % (filename,
self.geometry_type))
raise ReadLayerError(msg)
# Record attributes by name
number_of_fields = feature.GetFieldCount()
fields = {}
for j in range(number_of_fields):
name = feature.GetFieldDefnRef(j).GetName()
# FIXME (Ole): Ascertain the type of each field?
# We need to cast each appropriately?
# This is issue #66
# (https://github.com/AIFDR/riab/issues/66)
#feature_type = feature.GetFieldDefnRef(j).GetType()
fields[name] = feature.GetField(j)
# We do this because there is NaN problem on windows
# NaN value must be converted to _pseudo_in to solve the
# problem. But, when InaSAFE read the file, it'll be
# converted back to NaN value, so that NaN in InaSAFE is a
# numpy.nan
# please check https://github.com/AIFDR/inasafe/issues/269
# for more information
if fields[name] == _pseudo_inf:
fields[name] = float('nan')
#print 'Field', name, feature_type, j, fields[name]
data.append(fields)
# Store geometry coordinates as a compact numeric array
self.geometry = geometry
self.data = data
[docs] def write_to_file(self, filename, sublayer=None):
"""Save vector data to file
Args:
* filename: filename with extension .shp or .gml
* sublayer: Optional string for writing a sublayer. Ignored
unless we are writing to an sqlite file.
Note:
Shp limitation, if attribute names are longer than 10
characters they will be truncated. This is due to limitations in
the shp file driver and has to be done here since gdal v1.7 onwards
has changed its handling of this issue:
http://www.gdal.org/ogr/drv_shapefile.html
**For this reason we recommend writing to spatialite.**
"""
# Check file format
basename, extension = os.path.splitext(filename)
msg = ('Invalid file type for file %s. Only extensions '
'sqlite, shp or gml allowed.' % filename)
verify(extension in ['.sqlite', '.shp', '.gml'], msg)
driver = DRIVER_MAP[extension]
# FIXME (Ole): Tempory flagging of GML issue (ticket #18)
if extension == '.gml':
msg = ('OGR GML driver does not store geospatial reference.'
'This format is disabled for the time being. See '
'https://github.com/AIFDR/riab/issues/18')
raise WriteLayerError(msg)
# Derive layername from filename (excluding preceding dirs)
if sublayer is None or extension == '.shp':
layername = os.path.split(basename)[-1]
else:
layername = sublayer
# Get vector data
if self.is_polygon_data:
geometry = self.get_geometry(as_geometry_objects=True)
else:
geometry = self.get_geometry()
data = self.get_data()
N = len(geometry)
# Clear any previous file of this name (ogr does not overwrite)
try:
os.remove(filename)
except OSError:
pass
# Create new file with one layer
drv = ogr.GetDriverByName(driver)
if drv is None:
msg = 'OGR driver %s not available' % driver
raise WriteLayerError(msg)
ds = drv.CreateDataSource(filename)
if ds is None:
msg = 'Creation of output file %s failed' % filename
raise WriteLayerError(msg)
lyr = ds.CreateLayer(layername,
self.projection.spatial_reference,
self.geometry_type)
if lyr is None:
msg = 'Could not create layer %s' % layername
raise WriteLayerError(msg)
# Define attributes if any
store_attributes = False
fields = []
if data is not None:
if len(data) > 0:
try:
fields = data[0].keys()
except:
msg = ('Input parameter "attributes" was specified '
'but it does not contain list of dictionaries '
'with field information as expected. The first '
'element is %s' % data[0])
raise WriteLayerError(msg)
else:
# Establish OGR types for each element
ogrtypes = {}
for name in fields:
att = data[0][name]
py_type = type(att)
msg = ('Unknown type for storing vector '
'data: %s, %s' % (name, str(py_type)[1:-1]))
verify(py_type in TYPE_MAP, msg)
ogrtypes[name] = TYPE_MAP[py_type]
else:
#msg = ('Input parameter "data" was specified '
# 'but appears to be empty')
#raise InaSAFEError(msg)
pass
# Create attribute fields in layer
store_attributes = True
for name in fields:
fd = ogr.FieldDefn(name, ogrtypes[name])
# FIXME (Ole): Trying to address issue #16
# But it doesn't work and
# somehow changes the values of MMI in test
#width = max(128, len(name))
#print name, width
#fd.SetWidth(width)
# Silent handling of warnings like
# Warning 6: Normalized/laundered field name:
#'CONTENTS_LOSS_AUD' to 'CONTENTS_L'
gdal.PushErrorHandler('CPLQuietErrorHandler')
if lyr.CreateField(fd) != 0:
msg = 'Could not create field %s' % name
raise WriteLayerError(msg)
# Restore error handler
gdal.PopErrorHandler()
# Store geometry
geom = ogr.Geometry(self.geometry_type)
layer_def = lyr.GetLayerDefn()
for i in range(N):
# Create new feature instance
feature = ogr.Feature(layer_def)
# Store geometry and check
if self.is_point_data:
x = float(geometry[i][0])
y = float(geometry[i][1])
geom.SetPoint_2D(0, x, y)
elif self.is_line_data:
# FIXME (Ole): Change this to use array2ring instead!
#geom = ogr.Geometry(ogr.wkbLineString)
#linear_ring = array2ring(geometry[i])
#geom.AddGeometry(linear_ring)
wkt = array2wkt(geometry[i], geom_type='LINESTRING')
geom = ogr.CreateGeometryFromWkt(wkt)
elif self.is_polygon_data:
# Create polygon geometry
geom = ogr.Geometry(ogr.wkbPolygon)
# Add outer ring
linear_ring = array2ring(geometry[i].outer_ring)
geom.AddGeometry(linear_ring)
# Add inner rings if any
for A in geometry[i].inner_rings:
geom.AddGeometry(array2ring(A))
else:
msg = 'Geometry type %s not implemented' % self.geometry_type
raise WriteLayerError(msg)
feature.SetGeometry(geom)
G = feature.GetGeometryRef()
if G is None:
msg = 'Could not create GeometryRef for file %s' % filename
raise WriteLayerError(msg)
# Store attributes
if store_attributes:
for j, name in enumerate(fields):
actual_field_name = layer_def.GetFieldDefn(j).GetNameRef()
val = data[i][name]
if type(val) == numpy.ndarray:
# A singleton of type <type 'numpy.ndarray'> works
# for gdal version 1.6 but fails for version 1.8
# in SetField with error: NotImplementedError:
# Wrong number of arguments for overloaded function
val = float(val)
elif val is None:
val = ''
# We do this because there is NaN problem on windows
# NaN value must be converted to _pseudo_in to solve the
# problem. But, when InaSAFE read the file, it'll be
# converted back to NaN value, so that NaN in InaSAFE is a
# numpy.nan
# please check https://github.com/AIFDR/inasafe/issues/269
# for more information
if val != val:
val = _pseudo_inf
feature.SetField(actual_field_name, val)
# Save this feature
if lyr.CreateFeature(feature) != 0:
msg = 'Failed to create feature %i in file %s' % (i, filename)
raise WriteLayerError(msg)
feature.Destroy()
# Write keywords if any
write_keywords(self.keywords, basename + '.keywords')
# FIXME (Ole): Maybe store style_info
[docs] def copy(self):
"""Return copy of vector layer
This copy will be equal to self in the sense defined by __eq__
"""
if self.is_polygon_data:
geometry = self.get_geometry(copy=True, as_geometry_objects=True)
else:
geometry = self.get_geometry(copy=True)
return Vector(data=self.get_data(copy=True),
geometry=geometry,
projection=self.get_projection(),
keywords=self.get_keywords())
[docs] def get_attribute_names(self):
"""Get available attribute names
These are the ones that can be used with get_data
"""
return self.data[0].keys()
[docs] def get_data(self, attribute=None, index=None, copy=False):
"""Get vector attributes
Note:
Data is returned as a list where each entry is a dictionary of
attributes for one feature. Entries in get_geometry() and
get_data() are related as 1-to-1
If optional argument attribute is specified and a valid name,
then the list of values for that attribute is returned.
If optional argument index is specified on the that value will
be returned. Any value of index is ignored if attribute is None.
If optional argument copy is True and all attributes are requested,
a copy will be returned. Otherwise a pointer to the data is
returned.
"""
if hasattr(self, 'data'):
if attribute is None:
if copy:
return copy_module.deepcopy(self.data)
else:
return self.data
else:
msg = ('Specified attribute %s does not exist in '
'vector layer %s. Valid names are %s'
'' % (attribute, self, self.data[0].keys()))
verify(attribute in self.data[0], msg)
if index is None:
# Return all values for specified attribute
return [x[attribute] for x in self.data]
else:
# Return value for specified attribute and index
msg = ('Specified index must be either None or '
'an integer. I got %s' % index)
verify(isinstance(index, int), msg)
msg = ('Specified index must lie within the bounds '
'of vector layer %s which is [%i, %i]'
'' % (self, 0, len(self) - 1))
verify(0 <= index < len(self), msg)
return self.data[index][attribute]
else:
msg = 'Vector data instance does not have any attributes'
raise GetDataError(msg)
[docs] def get_geometry_type(self):
"""Return geometry type for vector layer
"""
return self.geometry_type
[docs] def get_geometry_name(self):
"""Return geometry name for vector layer
"""
return geometrytype2string(self.geometry_type)
[docs] def get_geometry(self, copy=False, as_geometry_objects=False):
"""Return geometry for vector layer.
Depending on the feature type, geometry is
geometry type output type
-----------------------------
point list of 2x1 array of longitudes and latitudes)
line list of arrays of coordinates
polygon list of arrays of coordinates
Optional boolean argument as_geometry_objects will change the return
value to a list of geometry objects rather than a list of arrays.
This currently only applies to polygon geometries
"""
if copy:
geometry = copy_module.deepcopy(self.geometry)
else:
geometry = self.geometry
if self.is_polygon_data:
if not as_geometry_objects:
geometry = [p.outer_ring for p in geometry]
else:
if as_geometry_objects:
msg = ('Argument as_geometry_objects can currently '
'be True only for polygon data')
raise InaSAFEError(msg)
return geometry
[docs] def get_bounding_box(self):
"""Get bounding box coordinates for vector layer.
Format is [West, South, East, North]
"""
e = self.extent
return [e[0], # West
e[2], # South
e[1], # East
e[3]] # North
[docs] def get_extrema(self, attribute=None):
"""Get min and max values from specified attribute
Return min, max
"""
if attribute is None:
msg = ('Valid attribute name must be specified in get_extrema '
'for vector layers. I got None.')
raise InaSAFEError(msg)
x = self.get_data(attribute)
return min(x), max(x)
[docs] def get_topN(self, attribute, N=10):
"""Get top N features
Args:
* attribute: The name of attribute where values are sought
* N: How many
Returns:
* layer: New vector layer with selected features
"""
# Input checks
msg = ('Specfied attribute must be a string. '
'I got %s' % (type(attribute)))
verify(isinstance(attribute, basestring), msg)
msg = 'Specified attribute was empty'
verify(attribute != '', msg)
msg = 'N must be a positive number. I got %i' % N
verify(N > 0, msg)
# Create list of values for specified attribute
values = self.get_data(attribute)
# Sort and select using Schwarzian transform
A = zip(values, self.data, self.geometry)
A.sort()
# Pick top N and unpack
data, geometry = zip(*A[-N:])[1:]
# Create new Vector instance and return
return Vector(data=data,
projection=self.get_projection(),
geometry=geometry,
keywords=self.get_keywords())
@property
def is_point_data(self):
return self.is_vector and self.geometry_type == ogr.wkbPoint
@property
def is_line_data(self):
return self.is_vector and self.geometry_type == ogr.wkbLineString
@property
def is_polygon_data(self):
return self.is_vector and self.geometry_type == ogr.wkbPolygon
@property
def is_multi_polygon_data(self):
return self.is_vector and self.geometry_type == ogr.wkbMultiPolygon
#----------------------------------
# Helper functions for class Vector
#----------------------------------
[docs]def convert_line_to_points(V, delta):
"""Convert line vector data to point vector data
Args:
* V: Vector layer with line data
* delta: Incremental step to find the points
Returns:
* Vector layer with point data and the same attributes as V
"""
msg = 'Input data %s must be line vector data' % V
verify(V.is_line_data, msg)
geometry = V.get_geometry()
data = V.get_data()
N = len(V)
# Calculate centroids for each polygon
points = []
new_data = []
for i in range(N):
c = points_along_line(geometry[i], delta)
# We need to create a data entry for each point.
# FIXME (Ole): What on earth is this?
# pylint: disable=W0621
new_data.extend([data[i] for _ in c])
# pylint: enable=W0621
points.extend(c)
# Create new point vector layer with same attributes and return
V = Vector(data=new_data,
projection=V.get_projection(),
geometry=points,
name='%s_point_data' % V.get_name(),
keywords=V.get_keywords())
return V
[docs]def convert_polygons_to_centroids(V):
"""Convert polygon vector data to point vector data
Args:
* V: Vector layer with polygon data
Returns:
* Vector layer with point data and the same attributes as V
"""
msg = 'Input data %s must be polygon vector data' % V
verify(V.is_polygon_data, msg)
geometry = V.get_geometry()
N = len(V)
# Calculate points for each polygon
centroids = []
for i in range(N):
c = calculate_polygon_centroid(geometry[i])
centroids.append(c)
# Create new point vector layer with same attributes and return
V = Vector(data=V.get_data(),
projection=V.get_projection(),
geometry=centroids,
name='%s_centroid_data' % V.get_name(),
keywords=V.get_keywords())
return V