Lyon, France/Buildings Heights Import

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Goals

The goal of that import is to update existing OSM buildings of Lyon with height information (see Key:height tag).

Context

Most of the buildings of Lyon are already into OSM, but height data is lacking: some quick stats using a coarse bounding box on the Métropole de Lyon shows that only 161 out of more than 600000 building have a height tag.

The métropole de Lyon has an OpenData website ( https://data.grandlyon.com/ ) where we can find a 3d model of the cities of this area, available under the "Licence ouverte 2.0" of Etalab ( https://download.data.grandlyon.com/files/grandlyon/LicenceOuverte.pdf ).

The data sets are under the cityGML format, which is a xml based format that encodes polygons representing buildings, differentiating wall and roofs.

The most difficult part of this import is determining what polygons in the 3d model are corresponding to structures in OSM. Indeed, Grand Lyon Data is way more detailed than OSM data, as shown on the following examples:

In green, data from Grand Lyon Data, in red, building ways from OSM
Église Sainte Blandine ( https://www.openstreetmap.org/way/45173893 ). In green, data from Grand Lyon Data, in red, building ways from OSM

That's why a "quality score" must be computed for each OSM building having one or more polygons matching with it. Polygons intersecting with an OSM building are selected only if more than XX% of their surface is common with the OSM building. Then, if more than YY% of the surface of the OSM building is covered by the polygons, the maximum height of the polygons are used as the height of the building.

Importing the 3d structure of buildings would be a way more complex job than just having their height, so it is not in the scope of this project.

Schedule

No schedule is ready yet.

Import Data

Background

Data source site: Open Data de Grand Lyon ( https://data.grandlyon.com/ )
Data license: https://download.data.grandlyon.com/files/grandlyon/LicenceOuverte.pdf
Type of license: Open License (OL/LO) 1.0

Data Sources

OSM Data Files

There's no prepared files yet.

Import Type

The import is designed to be launched one-time.

The creation of an .osc file will be automatic, and the import will be done through JOSM.

Data Preparation

Data Reduction & Simplification

There's no special reduction or simplification since the imported data are elevation ("Z") values, and buildings with a height tag already present won't be modified.

Tagging Plans

On each created changeset there will 2 tags :

  • source: Open Data de Grand Lyon Data ( https://data.grandlyon.com/ )
  • comment: Automatic import of buildings heights in métropole de Lyon, France.

Data Transformation

The only data transformation is to add a new height tag to the way-building, nothing more.

Data Merge Workflow

TBD

Team Approach

No team yet, source of scripts will be put on gitlab soon.

The import will be discussed on the talk-fr mailing list.

Workflow

  1. Download all data from Grand Lyon Data;
  2. Download OSM data for the Métropole de Lyon;
  3. Convert Grand Lyon Data from epsg:3946 to epsg:4326;
  4. For each building in the Métropole de Lyon, match the area with the corresponding 3d area, compute a quality score, and if it is good enough add the tag to the changeset.

Conflation

No big risk of conflation since the program doesn't touch buildings which have already a building:height tag.

QA

TODO

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