# 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:
#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"
impedance = "TravelTime"
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.MakeClosestFacilityLayer(network, layer_name,
impedance, "TRAVEL_FROM")
#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 and ensure that they are not
#located on restricted portions of the network. Use default field mappings
#and search tolerance
arcpy.na.AddLocations(layer_object, facilities_layer_name, facilities, "",
"", exclude_restricted_elements="EXCLUDE")
#Load tract centroids as incidents and ensure that they are not located on
#restricted portions of the network. 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, "",
exclude_restricted_elements="EXCLUDE")
#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)))