79 lines
4.3 KiB
Markdown
79 lines
4.3 KiB
Markdown
# Geocoders
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Geocoding is the ability to match an input **string representing a location - such as an address - to geographical coordinates**.
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Reverse geocoding is logically the opposite, matching **geographical coordinates to names of places**.
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This is needed to set correct address for events, and more easily find events with geographical data, for instance if you want to discover events happening near your current position.
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However, providing a geocoding service is quite expensive, especially if you want to cover the whole Earth.
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!!!note
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To give an idea of what hardware is required to self-host a geocoding service, we successfully used Addok, Pelias and Mimirsbrunn on a 8 core/16GB RAM machine without any issues **on French data**.
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## List of supported geocoders
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This is the list of all geocoders supported by Mobilizon. The current default one is [Nominatim](#nominatim) and uses the official OpenStreetMap instance.
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!!! bug
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Changing geocoder through `.env` configuration isn't currently supported by Mobilizon.
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Instead you need to edit the following line in `config.prod.exs`:
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```elixir
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config :mobilizon, Mobilizon.Service.Geospatial, service: Mobilizon.Service.Geospatial.Nominatim
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```
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And change `Nominatim` to one of the supported geocoders. This change might be overwritten when updating Mobilizon.
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### Nominatim
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[Nominatim](https://wiki.openstreetmap.org/wiki/Nominatim) is a GPL-2.0 licenced tool to search data by name and address. It's written in C and PHP and uses PostgreSQL.
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It's the current default search tool on the [OpenStreetMap homepage](https://www.openstreetmap.org).
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!!! warning
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When using the official Nominatim OpenStreetMap instance (default endpoint for this geocoder if not configured otherwise), you need to read and accept the [Usage Policy](https://operations.osmfoundation.org/policies/nominatim).
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Several companies provide hosted instances of Nominatim that you can query via an API, for example see [MapQuest Open Initiative](https://developer.mapquest.com/documentation/open/nominatim-search).
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### Addok
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[Addok](https://github.com/addok/addok) is a WTFPL licenced search engine for address (and only address). It's written in Python and uses Redis.
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It's used by French government for [adresse.data.gouv.fr](https://adresse.data.gouv.fr).
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!!! warning
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When using France's Addok instance at `api-adresse.data.gouv.fr` (default endpoint for this geocoder if not configured otherwise), you need to read and accept the [GCU](https://adresse.data.gouv.fr/cgu) (in French).
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### Photon
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[Photon](https://photon.komoot.de/) is an Apache 2.0 licenced search engine written in Java and powered by ElasticSearch.
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!!! warning
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The terms of use for the official instance (default endpoint for this geocoder if not configured otherwise) are simply the following:
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> You can use the API for your project, but please be fair - extensive usage will be throttled. We do not guarantee for the availability and usage might be subject of change in the future.
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### Pelias
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[Pelias](https://github.com/pelias/pelias) is a MIT licensed geocoder composed of several services written in NodeJS. It's powered by ElasticSearch.
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There's [Geocode Earth](https://geocode.earth/) SAAS that provides a Pelias API.
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They offer discounts for Open-Source projects. [See the pricing](https://geocode.earth/).
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### Mimirsbrunn
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[Mimirsbrunn](https://github.com/CanalTP/mimirsbrunn) is an AGPL-3.0 licensed geocoding written in Rust and powered by ElasticSearch.
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Mimirsbrunn is used by [Qwant Maps](https://www.qwant.com/maps) and [Navitia](https://www.navitia.io).
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### Google Maps
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[Google Maps](https://developers.google.com/maps/documentation/geocoding/intro) is a proprietary service that provides APIs for geocoding.
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They don't have a free plan, but offer credit when creating a new account. [See the pricing](https://cloud.google.com/maps-platform/pricing/).
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### MapQuest
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[MapQuest](https://developer.mapquest.com/documentation/open/geocoding-api/) is a proprietary service that provides APIs for geocoding.
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They offer a free plan. [See the pricing](https://developer.mapquest.com/plans).
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### More geocoding services
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Geocoding implementations are simple modules that need to implement the [`Mobilizon.Service.Geospatial.Provider` behaviour](https://framasoft.frama.io/mobilizon/backend/Mobilizon.Service.Geospatial.Provider.html), so feel free to write your own!
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