В следующем автономном скрипте Python показано, как с помощью инструмента CopyTraversedSourceFeatures можно найти улицы, относящиеся к маршрутам, идущим от центроидов переписных районов до ближайшей пожарной станции. Это позволяет определить, какие улицы чаще всего использовались в экстренных ситуациях.
# Name: CopyTraversedSourceFeatures_ex02.py
# Description: The scenario shows how to find the streets that are common to the
# routes between the closest fire station and the census tract
# centroids. These streets can be used to identify critical points
# in case of an emergency.
# Requirements: Network Analyst Extension
# Import system modules
import os
import arcpy
from arcpy import env
try:
# Check out Network Analyst license if available. Fail if the Network Analyst license is not available.
if arcpy.CheckExtension("network") == "Available":
arcpy.CheckOutExtension("network")
else:
raise arcpy.ExecuteError("Network Analyst Extension license is not available.")
# Set environment settings
output_dir = "C:/Data"
# The NA layer's data will be saved to the workspace specified here
env.workspace = os.path.join(output_dir, "Output.gdb")
env.overwriteOutput = True
env.qualifiedFieldNames = False
# Set local variables
input_gdb = "C:/Data/SanFrancisco.gdb"
output_gdb = "C:/Data/Output.gdb"
network = os.path.join(input_gdb, "Transportation", "Streets_ND")
layer_name = "EmergencyRoutes"
travel_mode = "Driving Time"
facilities = os.path.join(input_gdb, "Analysis", "FireStations")
incidents = os.path.join(input_gdb, "Analysis", "TractCentroids")
edge_frequency = os.path.join(output_gdb, "EdgeFrequency")
critical_streets = os.path.join(output_gdb, "CriticalStreets")
# Create a new closest facility analysis layer.
result_object = arcpy.na.MakeClosestFacilityAnalysisLayer(
network, layer_name, travel_mode, "FROM_FACILITIES"
)
# Get the layer object from the result object. The closest facility layer can
# now be referenced using the layer object.
layer_object = result_object.getOutput(0)
# Get the names of all the sublayers within the closest facility layer.
sublayer_names = arcpy.na.GetNAClassNames(layer_object)
# Stores the layer names that we will use later
facilities_layer_name = sublayer_names["Facilities"]
incidents_layer_name = sublayer_names["Incidents"]
# Load fire station features as facilities
arcpy.na.AddLocations(layer_object, facilities_layer_name, facilities)
# Load tract centroids as incidents. Map the ID field from Tract
# Centroids as the name for incidents using field mappings
field_mappings = arcpy.na.NAClassFieldMappings(
layer_object, incidents_layer_name
)
field_mappings['Name'].mappedFieldName = "ID"
arcpy.na.AddLocations(
layer_object, incidents_layer_name, incidents, field_mappings
)
# Solve the closest facility layer and copy the travered source features to
# the output geodatabase. Use default names for the output feature
# classes and table. Retrieve the first output, which is the traversed edges.
traversed_edges = arcpy.na.CopyTraversedSourceFeatures(
layer_object, output_gdb
).getOutput(0)
# Some streets might be traversed by more than one route. Streets traversed
# by many routes are the most critical emergency routes. Count the number of
# routes using each street.
arcpy.analysis.Frequency(
traversed_edges, edge_frequency, ["SourceOID", "SourceName"]
)
# The resulting edge features from CopyTraversedSourceFeatures may include
# clipped versions of the original street features because the Closest
# Facility route only traveled across part of the street feature. Select
# the complete street features from the original street feature class and
# copy them to output.
# Get the full path to the network dataset's streets feature class by
# describing the network dataset.
network_desc = arcpy.Describe(network)
edge_sources = network_desc.edgeSources
for es in edge_sources:
if es.name.lower() == "streets":
streets_source = os.path.join(os.path.dirname(network), es.name)
break
# Select the relevant streets based on overlap with the results from
# CopyTraversedSourceFeatures
streets_layer = arcpy.management.MakeFeatureLayer(
streets_source, "StreetsLayer"
)
arcpy.management.SelectLayerByLocation(
streets_layer, "SHARE_A_LINE_SEGMENT_WITH", traversed_edges
)
# Add the frequency information to the output feature class using JoinField
arcpy.management.JoinField(
streets_layer, "ObjectID", edge_frequency, "SourceOID", "FREQUENCY"
)
# Save the selected features to disk
arcpy.management.CopyFeatures(streets_layer, critical_streets)
# Delete the Frequency field from the street feature class
arcpy.management.DeleteField(streets_layer, "FREQUENCY")
print("Script completed successfully")
except Exception as e:
# If an error occurred, print line number and error message
import traceback, sys
tb = sys.exc_info()[2]
print("An error occurred on line %i" % tb.tb_lineno)
print(str(e))