crossroads segmentation

Crossroads segmentation is a python tool that produces automatic segmentations of data from OpenStreetMap.

Dependancies

• OSMnx that includes NetworkX and pandas
• argparse

Usage

The main script to use is get-crossroad-description.py. You will find a complete description of the possible parameters using the following command:

• get-crossroad-description.py --help

This tool is using OSMnx to download OpenStreetMap data from the selected region. It uses a cache, stored in cache/ directory. If a region has already been asked, it will use the cached data and not download it again. You can of course delete the cache directory to download again the data.

The location of the region can be choosen using coordinates (--by-coordinates LAT LNG) or using an predefined coordinate defined by a name (--by-name NAME). A radius (-r VALUE) with a default value of 150 meters can be adjusted to choose the size of the region to consider.

Several outputs are possible:

• to display the segmentation with all the crossings in the region (--display-segmentation), or only focussing on the main crossroad (--display-main-crossroad) closest to the input coordinate. This second display gives also the branches of the crossroad.
• to produce a text version of the selection (--to-text, --to-text-all) in the standard output
• to produce a json file that contains all the detected crossroads (--to-json-all FILENAME) or only the main one (--to-json FILENAME). Branches are also contained in this output.

The last stage of the segmentation algorithm consists in merging a ring of small crossroads into a large one. Parameters for this stagea are:

• a maximum number of crossroads in a ring (--max-cycle-elements NB), with default value of 10.
• a connection intensity (--connection-intensity NB) with typical values between 2 and 5, corresponding to distance threshold defined by this coefficient multiplied by an estimation of the branches width.

Several of these outputs (--to-json, --to-json-all, --display-main-crossroad) can be adjusted using the parameter --multiscale to describe the small crossroad that has been merged to produce the large ones.

Non regression tests

A very basic non regression test is provided in test directory. Usage:

• run first ./regenerate_references.sh
• run ./test.sh each time you want to check for regressions

Visual evaluation

A separated project has been split from this one in order to evaluate segmentation quality. See crossroads-evaluation.

Examples

./get-crossroad-description.py --by-name POC1 --display-main-crossroad --multiscale

./get-crossroad-description.py --by-name obélisque --display-segmentation -r 1000