Network skimming#

In this example, we show how to perform network skimming for Coquimbo, a city in La Serena Metropolitan Area in Chile.

See also

Several functions, methods, classes and modules are used in this example:

# Imports
from uuid import uuid4
from tempfile import gettempdir
from os.path import join
from aequilibrae.utils.create_example import create_example
# We create the example project inside our temp folder
fldr = join(gettempdir(), uuid4().hex)

project = create_example(fldr, "coquimbo")
import logging
import sys

When the project opens, we can tell the logger to direct all messages to the terminal as well

logger = project.logger
stdout_handler = logging.StreamHandler(sys.stdout)
formatter = logging.Formatter("%(asctime)s;%(levelname)s ; %(message)s")
stdout_handler.setFormatter(formatter)
logger.addHandler(stdout_handler)

Network Skimming#

import numpy as np

Let’s build all graphs

project.network.build_graphs()
# We get warnings that several fields in the project are filled with ``NaN``s.
# This is true, but we won't use those fields.

We grab the graph for cars

graph = project.network.graphs["c"]

# we also see what graphs are available
project.network.graphs.keys()

# let's say we want to minimize the distance
graph.set_graph("distance")

# And will skim distance while we are at it, other fields like ``free_flow_time`` or ``travel_time``
# can be added here as well
graph.set_skimming(["distance"])

# But let's say we only want a skim matrix for nodes 28-40, and 49-60 (inclusive),
# these happen to be a selection of western centroids.
graph.prepare_graph(np.array(list(range(28, 41)) + list(range(49, 91))))

And run the skimming

skm = graph.compute_skims()

Building network skims directly from the graph is more straightforward, though we could alternatively use the class NetworkSkimming to achieve the same result.

# from aequilibrae.paths import NetworkSkimming

# skm = NetworkSkimming(graph)
# skm.execute()

The result is an AequilibraEMatrix object

skims = skm.results.skims

# Which we can manipulate directly from its temp file, if we wish
skims.matrices[:3, :3, :]

Or access each matrix, lets just look at the first 3x3

skims.distance[:3, :3]

We can save it to the project if we want

skm.save_to_project("base_skims")

We can also retrieve this skim record to write something to its description

matrices = project.matrices
mat_record = matrices.get_record("base_skims")
mat_record.description = "minimized distance while also skimming distance for just a few nodes"
mat_record.save()
project.close()

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