Summary
Provides access to analysis properties from a service area network analysis layer. The GetSolverProperties function is used to obtain a ServiceAreaSolverProperties object from a service area network analysis layer.
Discussion
The ServiceAreaSolverProperties object provides read and write access to all the analysis properties of a service area network analysis layer. The object can be used to modify the desired analysis properties of the service area layer, and the corresponding layer can be resolved to determine the appropriate results. A new service area layer can be created using the Make Service Area Analysis Layer geoprocessing tool. Obtaining the ServiceAreaSolverProperties object from a new service area layer allows you to reuse the existing layer for subsequent analyses rather than create a layer for each analysis, which can be slow.
After modifying the properties of the ServiceAreaSolverProperties object, the corresponding layer can be immediately used with other functions and geoprocessing tools. There is no refresh or update of the layer required to honor the changes modified through the object.
Properties
| Property | Explanation | Data Type |
| accumulators (Read and Write) | Provides the ability to get or set a list of network cost attributes that are accumulated as part of the analysis. An empty list, [], indicates that no cost attributes are accumulated. | String |
| attributeParameters (Read and Write) | Provides the ability to get or set the parameterized attributes to be used in the analysis. The property returns a Python dictionary. The dictionary key is a two-value tuple consisting of the attribute name and the parameter name. The value for each item in the dictionary is the parameter value. Parameterized network attributes are used to model some dynamic aspect of an attribute's value. For example, a tunnel with a height restriction of 12 feet can be modeled using a parameter. In this case, the vehicle's height in feet should be specified as the parameter value. If the vehicle is taller than 12 feet, this restriction will then evaluate to True, thereby restricting travel through the tunnel. Similarly, a bridge could have a parameter to specify a weight restriction. Attempting to modify the attributeParameters property in place won't result in updated values. Instead, you should always use a new dictionary object to set values for the property. The following two code blocks demonstrate the difference between these two approaches. Do not attempt to modify the attributeParameters property in place; this coding method will not work. Modify the attributeParameters property using a new dictionary object. | Dictionary |
| defaultBreaks (Read and Write) | Provides the ability to get or set the impedance values, indicating the extent of the service area to be calculated. Multiple polygon breaks can be set to create concentric service areas. For instance, to find 2-, 3-, and 5-minute service areas for the same facility, specify the value as [2, 3, 5]. | Double |
| excludeSources (Read and Write) | Provides the ability to get or set the list of network sources to be excluded when generating the polygons. The geometry of traversed elements from the excluded sources will be omitted from all polygons. An empty list, [], indicates that no network sources are excluded. | String |
| ignoreInvalidLocations (Read and Write) | Specifies whether invalid input locations will be ignored. Typically, locations are invalid if they cannot be located on the network. When invalid locations are ignored, the solver will skip them and attempt to perform the analysis using the remaining locations.
| String |
| impedance (Read and Write) | Provides the ability to get or set the network cost attribute used as impedance. This cost attribute is accumulated while determining the service area. | String |
| includeNetworkSourceFields (Read and Write) | Controls whether additional fields from the underlying source features traversed during the analysis are added to the service area lines. The following is a list of possible values:
| String |
| lineOverlap (Read and Write) | Controls whether overlapping lines are generated when the service area lines are computed. The following is a list of possible values:
| String |
| lineType (Read and Write) | Provides the ability to get or set the type of service area lines to be generated from the analysis. The following is a list of possible values:
| String |
| polygonMerge (Read and Write) | Controls whether polygons that share similar break values are merged. This option is applicable only when generating polygons for multiple facilities. The following is a list of possible values:
| String |
| polygonNesting (Read and Write) | Controls whether concentric service area polygons are created as disks or rings. This option is applicable only when multiple break values are specified for the facilities. The following is a list of possible values:
| String |
| polygonType (Read and Write) | Provides the ability to get or set the type of polygons to be generated. The following is a list of possible values:
| String |
| restrictions (Read and Write) | Provides the ability to get or set a list of restriction attributes that are applied for the analysis. An empty list, [], indicates that no restriction attributes are used for the analysis. | String |
| solverName (Read Only) | Returns the name of the solver being referenced by the network analysis layer used to obtain the solver properties object. The property always returns the string value Service Area Solver when accessed from a ServiceAreaSolverProperties object. | String |
| splitLinesAtBreaks (Read and Write) | Controls whether service area lines are split when they cross a break value. The following is a list of possible values:
| String |
| timeOfDay (Read and Write) | Provides the ability to get or set the time to depart from or arrive at the facilities. The interpretation of this value depends on whether travel is toward or away from the facilities. It represents the departure time if the travelDirection property is set to TRAVEL_FROM and represents the arrival time if the travelDirection property is set to TRAVEL_TO. A value of None can be used to specify that no date and time should be used. Instead of using a particular date, a day of the week can be specified using the following dates:
For example, to specify that the departure from facilities should occur at 8:00 a.m. on Friday, specify the value as datetime.datetime(1900, 1, 5, 8,0,0). The timeZoneUsage parameter specifies whether the date and time refer to UTC or the time zone in which the facilities are located. | DateTime |
| timeZoneUsage (Read and Write) | Specifies the time zone or zones of the timeOfDay parameter.
Irrespective of the timeZoneUsage setting, all facilities must be in the same time zone when timeOfDay has a nonnull value and polygonMerge is set to create merged or nonoverlapping polygons. | String |
| travelDirection (Read and Write) | Controls the direction in which the impedance is accumulated during service area analysis. The following is a list of possible values:
| String |
| travelMode (Read Only) | Accesses the travel mode set on a network analysis layer as an arcpy.na.TravelMode object. | Object |
| trimDistance (Read and Write) | Provides the ability to get or set the distance within which the service area polygons are trimmed. The property value includes a numeric value and a unit for the distance separated by a space; for example, to specify a trim distance of 100 Meters, use "100 Meters". | String |
| trimPolygons (Read and Write) | Controls whether the service area polygons are trimmed. The following is a list of possible values:
| String |
| useHierarchy (Read and Write) | Controls the use of the hierarchy attribute while performing the analysis. The following is a list of possible values:
| String |
| uTurns (Read and Write) | Provides the ability to get or set the policy that indicates how the U-turns at junctions that could occur during network traversal between stops are being managed by the solver. The following is a list of possible values:
| String |
Method Overview
| Method | Explanation |
| applyTravelMode (travel_mode) | Updates the analysis properties of a network analyst layer based on a travel mode object. The updated network analyst layer can then be solved to complete the analysis. |
Methods
applyTravelMode (travel_mode)
| Parameter | Explanation | Data Type |
travel_mode | A variable that references a travel mode object derived from a network dataset. A list of travel mode objects can be obtained by calling the arcpy.na.GetTravelModes function. | Object |
When a network analyst layer is created, it is assigned default values for all of its analysis properties. The individual analysis properties can be updated using a solver properties object obtained from the network analyst layer. A travel mode stores a predefined set of analysis settings that help to perform a particular analysis, such as a walking time travel mode that stores the analysis settings required to perform a time-based walking analysis.
Using the applyTravelMode method, all the analysis settings that are defined in a travel mode can be applied at once. After the analysis properties are updated, the network analyst layer can be solved to complete the analysis.
If there is an error when updating the solver properties, such as when the provided travel mode references properties that don't exist on the current network dataset or references properties that are no longer applicable to the network dataset that was used to create the network analyst layer corresponding to the solver properties object, no exceptions are raised. The method will execute successfully, but you will get errors when you try to solve such a network analyst layer.
If the travel_mode parameter does not reference a travel mode object or a string, a TypeError exception is raised. If the travel_mode parameter references a string and the string cannot be internally converted to a valid string representation of a travel mode object, a ValueError exception is raised.
Code sample
This script shows how to update the Service Area solver properties through a full workflow. This is based on the tutorial network dataset of the San Francisco region.
# Name: ServiceAreaSolverProperties_Workflow.py
# Description: Finds the regions fire stations can reach within four minutes
# as the initial assesment of the coverage of the region. We will
# then change the break values to 1, 4, and 10 minutes to see a
# better picture of coverage
# Requirements: Network Analyst Extension
# Import system modules
import arcpy
from arcpy import env
import os
import datetime
try:
# Check out the 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
# Set local variables
input_gdb = "C:/Data/SanFrancisco.gdb"
network = os.path.join(input_gdb, "Transportation", "Streets_ND")
layer_name = "FireHouseRegions"
travel_mode = "Driving Time"
direction = "FROM_FACILITIES"
cutoffs = 4
in_facilities = os.path.join(input_gdb, "Analysis/FireStations")
four_minute_polygons = os.path.join(output_dir, "Output.gdb", "four_minute_polygons")
ten_minute_polygons = os.path.join(output_dir, "Output.gdb", "ten_minute_polygons")
# Create a new Service Area layer. Fire stations are concerned with the
# drive times away from the fire stations to the incidents.
result_object = arcpy.na.MakeServiceAreaAnalysisLayer(network,
layer_name, travel_mode,
direction, cutoffs)
# Get the layer object form the result object. The service area layer
# can now be referenced using the layer object.
layer_object = result_object.getOutput(0)
# Get the names of all the sublayers within the service area layer.
sub_layer_names = arcpy.na.GetNAClassNames(layer_object)
# Store the layer names that we will use later
facilities_layer_name = sub_layer_names["Facilities"]
polygons_layer_name = sub_layer_names["SAPolygons"]
# Load the fire station locations as facilities.
arcpy.na.AddLocations(layer_object, facilities_layer_name, in_facilities,
"", "")
# Solve the service area layer
arcpy.na.Solve(layer_object)
# Save the resulting polygon sublayer
arcpy.management.CopyFeatures(polygons_layer_name, four_minute_polygons)
# Get the solver properties object from the service area layer
solverProps = arcpy.na.GetSolverProperties(layer_object)
# Update the breaks to 1, 4, and 10 minutes
solverProps.defaultBreaks = [1, 4, 10]
# Solve the service area layer
arcpy.na.Solve(layer_object)
# Save the resulting polygon sublayer
arcpy.management.CopyFeatures(polygons_layer_name, ten_minute_polygons)
except Exception as e:
# If an error occurred, print line number and error message
import traceback
import sys
tb = sys.exc_info()[2]
print ("An error occurred on line %i" % tb.tb_lineno)
print (str(e))This script shows how to apply the TruckingTime travel mode to an existing layer.
#Get the service area layer object from a layer named "Service Area" in the map
doc = arcpy.mp.ArcGISProject('current')
map_obj = doc.listMaps()[0]
sa_layer = map_obj.listLayers('Service Area')[0]
#Get the Trucking Time travel mode from the network dataset
desc = arcpy.Describe(sa_layer)
travel_modes = arcpy.na.GetTravelModes(desc.network.catalogPath)
trucking_mode = travel_modes["Trucking Time"]
#Apply the travel mode to the analysis layer
solver_properties = arcpy.na.GetSolverProperties(sa_layer)
solver_properties.applyTravelMode(trucking_mode)