Snap points to a line string keeping a given order intact
Project description
PySnapping
Snap points to a line string keeping a given order or spacing intact.
The PySnapping python library helps to solve the problem of snapping an ordered sequence of points to a line string, respecting the given input order.
The motivation for this library is to solve the problem of snapping stops onto vehicle trajectories in the GTFS format with inaccurate or missing kilometrage.
In order to be able to work with metric parameters and to treat data with large extent located anywhere on the world, we use the EPSG:4978 Cartesian 3D geocentric coordinate system for the internal representation.
The library aims to automatically classify kilometrage information as trusted or untrusted and fills missing data and corrects bogus data by interpolation/extrapolation if possible. Trusted points are always snapped as given by the kilometrage. In between trusted points, an approximate iterative scheme is used to snap all untrusted points such that the order or minimum spacing conditions are not violated.
Installation
Install the latest stable release from PyPI with pip:
pip install pysnapping
Modules
Linear Referencing
The pysnapping.linear_referencing
module contains low-level classes and functions for referencing points along
linear features in N-dimensions built on top of numpy
. This contains interpolation/extrapolation along a line string
and data structures optimized for projecting points to substrings of a line string.
Ordering
The pysnapping.ordering
module contains functions to check and fix the order of a sequence of floats,
respecting certain boundary conditions and spacings using the method of quadratic programming with the cvxpy
library.
Utils
The pysnapping.util
module contains common helper functions used in other parts of the library.
Snapping
The pysanpping.snap
module is the main entry point for users of the pysnapping
library and
provides the classes needed to use the library.
Usage
The typical usage pattern is to create a pysnapping.snap.DubiousTrajectory
instance which represents
a vehicle trajectory with dubious kilometrage and a pysnapping.snap.DubiousTrajectoryTrip
dtrip
which represents
a trip along such a trajectory with dubious kilometrage for the stops and dubious timing information.
Then dtrip.to_trajectory_trip
can be used to get a pysnapping.snap.TrajectorTrip
trip
with well defined
metric kilometrage. trip.trajectory
then refers to a pysnapping.snap.Trajectory
instance with well defined metric
kilometrage. The conversion can be controlled with parameters given by a pysnapping.snap.SnappingParams
instance.
The trip.snap_trip_points
method can be used to snap the trip points onto the trajectory, resulting in
a pysnapping.snap.SnappedTripPoints
instance snapped
. Then you can e.g. split the trajectory at the stops
using the snapped.get_inter_point_ls_coords_in_travel_direction
method.
A more detailed usage example (e.g. how to process GTFS input) is planned but not available yet. Until then, please also check the docstrings and source code for additional usage hints/possibilities.
Issue Tracker
Please use the GitHub issue tracker to report bugs/issues.
Development
Contributing
If you want to contribute to the pysnapping library, you can make a pull request at GitHub. Before working on major features/changes, please consider contacting us about your plans. See our GitHub page for contact details.
Editable Installation
Clone this repo and enter the corresponding directory. Create a virtual environment, then install frozen requirements, dev-requirements and this library in editable mode:
python3.7 -m venv env
. env/bin/activate
pip install -U pip
pip install -r requirements.txt -r dev-requirements.txt -e .
Keep env activated for all following instructions.
Pre-Commit Hooks
Enable pre-commit hooks:
pre-commit install
From time to time (not automated yet) run
pre-commit autoupdate
to update frozen revs.
Run tests
Run tests and analyze code coverage:
pytest --cov=pysnapping --cov-report term --cov-fail-under=85 pysnapping
Project details
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Source Distribution
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