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63 lines
3.3 KiB
63 lines
3.3 KiB
6 years ago
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# Pelias services
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A running Pelias installation is composed of several different services. Each service is well suited
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to a particular task.
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## Service Use Cases
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Here's a list of which services provide which features in Pelias. If you don't need everything Pelias
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does, you may be able to get by without installing and running all the Pelias services
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| Service | /v1/search | /v1/autocomplete | /v1/reverse | /v1/reverse (coarse) | Multiple language support (any endpoint) |
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| ------ | ----- | ----- | --------- | ------- | ----- |
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| API | **required** | **required** | **required** | **required** | **required** |
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| Placeholder | **required** | | | | **required** |
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| Libpostal | **required** | | | | |
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| PIP | | | recommended | **required** | |
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| Interpolation | optional | | | | |
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## Descriptions
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### [API](https://github.com/pelias/api)
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This is the core of Pelias. It talks to all other services (if available), Elasticsearch, and
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provides the interface for all queries to Pelias.
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### [Placeholder](https://github.com/pelias/placeholder)
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Placeholder is used specifically to handle the relational component of geocoding. Placeholder
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understands, for example, that Paris is a city in a country called France, but that there is another
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city called Paris in the state of Texas, USA.
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Placeholder also stores the translations of administrative areas in multiple languages. Therefore it
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is required if any support for multiple languages is desired.
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Currently, Placeholder is used only for forward geocoding on the `/v1/search` endpoint. In the
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future, it will also be used for autocomplete.
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### Libpostal
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Libpostal is a library that provides an address parser using a statistical natural language processing
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model trained on OpenStreetMap, OpenAddresses, and other open data. It is quite good at parsing
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fully specified input, but cannot handle autocomplete very well.
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The data required for Libpostal to run is around 3GB, and has to be loaded into memory, so this
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service is fairly expensive to run, even for small installations.
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Unlike the other Pelias services, we didn't actually write a Pelias Libpostal service. We recommend
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using the [go-whosonfirst-libpostal](https://github.com/whosonfirst/go-whosonfirst-libpostal)
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service created by the [Who's on First](https://whosonfirst.org) team.
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## [Point-in-Polygon (PIP)](https://github.com/pelias/pip-service)
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The PIP service loads polygon data representing the boundaries of cities, states, regions, countries
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etc into memory, and can perform calculations on that geometric data. Its used to determine if a
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given point lies in a particular polygon. Thus, it's highly recommended for reverse geocoding.
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## [Interpolation](https://github.com/pelias/interpolation)
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The interpolation service combines street geometries with known addresses and address ranges, to
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allow estimating the position of addresses that might exist, but aren't in existing open
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data sources. It is only used by the `/v1/search` endpoint, but [autocomplete support may be added in
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the future](https://github.com/pelias/interpolation/issues/131).
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