6. Use examples

This page is still under development, so most of the headers are just place-holders for the actual examples

Note

The examples provided here are not meant as a through description of AequilibraE’s capabilities. For that, please look into the API documentation or email aequilibrae@googlegroups.com

6.1. Logging

AequilibraE uses Python’s standard logging library to a file called aequilibrae.log, but the output folder for this logging can be changed to a custom system folder by altering the parameter system –> logging_directory on the parameters file.

As an example, one could do programatically change the output folder to ‘D:/myProject/logs’ by doing the following:

from aequilibrae import Parameters

fldr = 'D:/myProject/logs'

p = Parameters()
p.parameters['system']['logging_directory'] =  fldr
p.writeback()

The other useful resource, especially during model debugging it to also show all log messages directly on the screen. Doing that requires a little knowledge of the Python Logging library, but it is just as easy:

from aequilibrae import logger
import logging

stdout_handler = logging.StreamHandler(sys.stdout)
logger.addHandler(stdout_handler)

6.2. Parameters module

Several examples on how to manipulate the parameters within AequilibraE have been shown in other parts of this tutorial.

However, in case you ever have trouble with parameter changes you have made, you can always revert them to their default values. But remember, ALL CHANGES WILL BE LOST.

from aequilibrae import Parameters

fldr = 'D:/myProject/logs'

p = Parameters()
p.reset_default()

6.3. Project module

Let’s suppose one wants to create project files for a list of 20 cities around the world with their complete networks downloaded from Open Street Maps and place them on a local folder for analysis at a later time.

from aequilibrae.project import Project
import os

cities = ["Darwin, Australia",
          "Karlsruhe, Germany",
          "London, UK",
          "Paris, France",
          "Shanghai, China",
          "Sao Paulo, Brazil",
          "Rio de Janeiro, Brazil",
          "Los Angeles, USA",
          "New York, USA",
          "Mexico City, Mexico",
          "Berlin, Germany",
          "Vancouver, Canada",
          "Montreal, Canada",
          "Toronto, Canada",
          "Madrid, Spain",
          "Lisbon, Portugal",
          "Rome, Italy",
          "Perth, Australia",
          "Hobart, Australia",
          "Auckland, New Zealand"]

for city in cities:
    pth = f'd:/net_tests/{city}.sqlite'

    p = Project(pth, True)
    p.network.create_from_osm(place_name=city)
    p.conn.close()
    del p

6.4. Paths module

from aequilibrae.paths import allOrNothing
from aequilibrae.paths import path_computation
from aequilibrae.paths.results import AssignmentResults as asgr
from aequilibrae.paths.results import PathResults as pthr

6.4.1. Path computation

6.4.2. Skimming

Let’s suppose you want to compute travel times between all zone on your network. In that case, you need only a graph that you have previously built, and the list of skims you want to compute.

from aequilibrae.paths.results import SkimResults as skmr
from aequilibrae.paths import Graph
from aequilibrae.paths import NetworkSkimming

# We instantiate the graph and load it from disk (say you created it using the QGIS GUI
g = Graph()
g.load_from_disk(aeg_pth)

# You now have to set the graph for what you want
# In this case, we are computing fastest path (minimizing free flow time)
# We are also **blocking** paths from going through centroids
g.set_graph(cost_field='fftime', block_centroid_flows=True)

# We will be skimming for fftime **AND** length along the way
g.set_skimming(['fftime', 'length'])

# We instantiate the skim results and prepare it to have results compatible with the graph provided
result = skmr()
result.prepare(g)

# We create the network skimming object and execute it
# This is multi-threaded, so if the network is too big, prepare for a slow computer
skm = NetworkSkimming(g, result)
skm.execute()

If you want to use fewer cores for this computation (which also saves memory), you also can do it You just need to use the method set_cores before you run the skimming. Ideally it is done before preparing it

result = skmr()
result.set_cores(3)
result.prepare(g)

And if you want to compute skims between all nodes in the network, all you need to do is to make sure the list of centroids in your graph is updated to include all nodes in the graph

from aequilibrae.paths.results import SkimResults as skmr
from aequilibrae.paths import Graph
from aequilibrae.paths import NetworkSkimming

g = Graph()
g.load_from_disk(aeg_pth)

# Let's keep the original list of centroids in case we want to use it again
orig_centr = g.centroids

# Now we set the list of centroids to include all nodes in the network
g.prepare_graph(g.all_nodes)

# And continue **almost** like we did before
# We just need to remember to NOT block paths through centroids. Otherwise there will be no paths available
g.set_graph(cost_field='fftime', block_centroid_flows=False)
g.set_skimming('fftime')

result = skmr()
result.prepare(g)

skm = NetworkSkimming(g, result)
skm.execute()

Setting skimming after setting the graph is CRITICAL, and the skim matrices are part of the result object.

You can save the results to your place of choice in AequilibraE format or export to OMX or CSV

result.skims.export('path/to/desired/folder/file_name.omx')

result.skims.export('path/to/desired/folder/file_name.csv')

result.skims.copy('path/to/desired/folder/file_name.aem')

6.4.3. Traffic Assignment

some code

6.4.4. Advanced usage: Building a Graph

Let’s suppose now that you are interested in creating links from a bespoke procedure. For the purpose of this example, let’s say you have a sparse matrix representing a graph as an adjacency matrix

from aequilibrae.paths import Graph
from aequilibrae import reserved_fields
from scipy.sparse import coo_matrix

# original_adjacency_matrix is a sparse matrix where positive values are actual links
# where the value of the cell is the distance in that link

# We create the sparse matrix in proper sparse matrix format
sparse_graph = coo_matrix(original_adjacency_matrix)

# We create the structure to create the network
all_types = [k._Graph__integer_type,
             k._Graph__integer_type,
             k._Graph__integer_type,
             np.int8,
             k._Graph__float_type,
             k._Graph__float_type]

all_titles = [reserved_fields.link_id,
              reserved_fields.a_node,
              reserved_fields.b_node,
              reserved_fields.direction,
             "length_ab",
             "length_ba"]

dt = [(t, d) for t, d in zip(all_titles, all_types)]

# Number of links
num_links = sparse_graph.data.shape[0]

my_graph = Graph()
my_graph.network = np.zeros(links, dtype=dt)

my_graph.network[reserved_fields.link_id] = np.arange(links) + 1
my_graph.network[reserved_fields.a_node] = sparse_graph.row
my_graph.network[reserved_fields.b_node] = sparse_graph.col
my_graph.network["length_ab"] = sparse_graph.data

# If the links are directed (from A to B), direction is 1. If bi-directional, use zeros
my_graph.network[reserved_fields.direction] = np.ones(links)

# If uni-directional from A to B the value is not used
my_graph.network["length_ba"] = mat.data * 10000

# Let's say that all nodes in the network are centroids
list_of_centroids =  np.arange(max(sparse_graph.shape[0], sparse_graph.shape[0])+ 1)
centroids_list = np.array(list_of_centroids)

my_graph.type_loaded = 'NETWORK'
my_graph.status = 'OK'
my_graph.network_ok = True
my_graph.prepare_graph(centroids_list)

This usage is really advanced, and very rarely not-necessary. Make sure to know what you are doing before going down this route

6.5. Trip distribution

The support for trip distribution in AequilibraE is not very comprehensive, mostly because of the loss of relevance that such type of model has suffered in the last decade.

However, it is possible to calibrate and apply synthetic gravity models and to perform Iterative Proportional Fitting (IPF) with really high performance, which might be of use in many applications other than traditional distribution.

6.5.1. Synthetic gravity calibration

some code

6.5.2. Synthetic gravity application

In this example, imagine that you have your demographic information in an sqlite database and that you have already computed your skim matrix.

It is also important to notice that it is crucial to have consistent data, such as same set of zones (indices) in both the demographics and the impedance matrix.

import pandas as pd
import sqlite3

from aequilibrae.matrix import AequilibraeMatrix
from aequilibrae.matrix import AequilibraeData

from aequilibrae.distribution import SyntheticGravityModel
from aequilibrae.distribution import GravityApplication


# We define the model we will use
model = SyntheticGravityModel()

# Before adding a parameter to the model, you need to define the model functional form
model.function = "GAMMA" # "EXPO" or "POWER"

# Only the parameter(s) applicable to the chosen functional form will have any effect
model.alpha = 0.1
model.beta = 0.0001

# Or you can load the model from a file
model.load('path/to/model/file')

# We load the impedance matrix
matrix = AequilibraeMatrix()
matrix.load('path/to/impedance_matrix.aem')
matrix.computational_view(['distance'])

# We create the vectors we will use
conn = sqlite3.connect('path/to/demographics/database')
query = "SELECT zone_id, population, employment FROM demographics;"
df = pd.read_sql_query(query,conn)

index = df.zone_id.values[:]
zones = index.shape[0]

# You create the vectors you would have
df = df.assign(production=df.population * 3.0)
df = df.assign(attraction=df.employment * 4.0)

# We create the vector database
args = {"entries": zones, "field_names": ["productions", "attractions"],
    "data_types": [np.float64, np.float64], "memory_mode": True}
vectors = AequilibraeData()
vectors.create_empty(**args)

# Assign the data to the vector object
vectors.productions[:] = df.production.values[:]
vectors.attractions[:] = df.attraction.values[:]
vectors.index[:] = zones[:]

# Balance the vectors
vectors.attractions[:] *= vectors.productions.sum() / vectors.attractions.sum()

args = {"impedance": matrix,
        "rows": vectors,
        "row_field": "productions",
        "model": model,
        "columns": vectors,
        "column_field": "attractions",
        "output": 'path/to/output/matrix.aem',
        "nan_as_zero":True
        }

gravity = GravityApplication(**args)
gravity.apply()

6.5.3. Iterative Proportional Fitting (IPF)

The implementation of IPF is fully vectorized and leverages all the speed of NumPy, but it does not include the fancy multithreading implemented in path computation.

Please note that the AequilibraE matrix used as input is OVERWRITTEN by the IPF

import pandas as pd
from aequilibrae.distribution import Ipf
from aequilibrae.matrix import AequilibraeMatrix
from aequilibrae.matrix import AequilibraeData

matrix = AequilibraeMatrix()

# Here we can create from OMX or load from an AequilibraE matrix.
matrix.create_from_omx(path/to/aequilibrae_matrix, path/to/omxfile)

# The matrix will be operated one (see the note on overwriting), so it does
# not make sense load an OMX matrix


source_vectors = pd.read_csv(path/to/CSVs)
zones = source_vectors.zone.shape[0]

args = {"entries": zones, "field_names": ["productions", "attractions"],
        "data_types": [np.float64, np.float64], "memory_mode": True}

vectors = AequilibraEData()
vectors.create_empty(**args)

vectors.productions[:] = source_vectors.productions[:]
vectors.attractions[:] = source_vectors.attractions[:]

# We assume that the indices would be sorted and that they would match the matrix indices
vectors.index[:] = source_vectors.zones[:]

args = {
        "matrix": matrix, "rows": vectors, "row_field": "productions", "columns": vectors,
        "column_field": "attractions", "nan_as_zero": False}

fratar = Ipf(**args)
fratar.fit()

# We can get back to our OMX matrix in the end
matrix.export(path/to_omx/output)

6.6. Transit

We only have import for now, and it is likely to not work on Windows if you want the geometries

6.6.1. GTFS import

some code

6.7. Matrices

Lets say we want to Import the freight matrices provided with FAF into AequilibraE’s matrix format in order to create some Delaunay Lines in QGIS or to perform traffic assignment

6.7.1. Required data

• FAF Matrices

• Zones System

6.7.2. Useful Information

• FAF overview

• FAF User Guide

• The blog post (with data)

6.7.3. The code

We import all libraries we will need, including the AequilibraE

import pandas as pd
import numpy as np
import os
from aequilibrae.matrix import AequilibraeMatrix
from scipy.sparse import coo_matrix

Now we set all the paths for files and parameters we need and import the matrices into a Pandas DataFrame

data_folder = 'Y:/ALL DATA/DATA/Pedro/Professional/Data/USA/FAF/4.4'
data_file = 'FAF4.4_HiLoForecasts.csv'
sctg_names_file = 'sctg_codes.csv'  # Simplified to 50 characters, which is AequilibraE's limit
output_folder = data_folder

matrices = pd.read_csv(os.path.join(data_folder, data_file), low_memory=False)

We import the sctg codes

sctg_names = pd.read_csv(os.path.join(data_folder, sctg_names_file), low_memory=False)
sctg_names.set_index('Code', inplace=True)
sctg_descr = list(sctg_names['Commodity Description'])

We now process the matrices to collect all the data we need, such as:

• List of zones

• CSTG codes

• Matrices/scenarios we are importing

all_zones = np.array(sorted(list(set( list(matrices.dms_orig.unique()) + list(matrices.dms_dest.unique())))))

# Count them and create a 0-based index
num_zones = all_zones.shape[0]
idx = np.arange(num_zones)

# Creates the indexing dataframes
origs = pd.DataFrame({"from_index": all_zones, "from":idx})
dests = pd.DataFrame({"to_index": all_zones, "to":idx})

# adds the new index columns to the pandas dataframe
matrices = matrices.merge(origs, left_on='dms_orig', right_on='from_index', how='left')
matrices = matrices.merge(dests, left_on='dms_dest', right_on='to_index', how='left')

# Lists sctg codes and all the years/scenarios we have matrices for
mat_years = [x for x in matrices.columns if 'tons' in x]
sctg_codes = matrices.sctg2.unique()

We now import one matrix for each year, saving all the SCTG codes as different matrix cores in our zoning system

# aggregate the matrix according to the relevant criteria
agg_matrix = matrices.groupby(['from', 'to', 'sctg2'])[mat_years].sum()

# returns the indices
agg_matrix.reset_index(inplace=True)


for y in mat_years:
    mat = AequilibraeMatrix()

    # Here it does not make sense to use OMX
    # If one wants to create an OMX from other data sources, openmatrix is
    # the library to use
    kwargs = {'file_name': os.path.join(output_folder, y + '.aem'),
              'zones': num_zones,
              'matrix_names': sctg_descr}

    mat.create_empty(**kwargs)
    mat.index[:] = all_zones[:]
    # for all sctg codes
    for i in sctg_names.index:
        prod_name = sctg_names['Commodity Description'][i]
        mat_filtered_sctg = agg_matrix[agg_matrix.sctg2 == i]

        m = coo_matrix((mat_filtered_sctg[y], (mat_filtered_sctg['from'], mat_filtered_sctg['to'])),
                                           shape=(num_zones, num_zones)).toarray().astype(np.float64)

        mat.matrix[prod_name][:,:] = m[:,:]

    mat.close()