General Concepts

This article tries to explain some general concepts of libosmscout.

Import

Libosmscout has its own internal representation of OSM data. This is necssary to offer fast access of the data and reduce the size of the data on disk. Standard export formats like .osm or *.osm.pbf files are used as data dump from the OSM SQL database for further processing and are designed for fast, index random data access.

For importing the data the Import tool is used. The import tool generates a custom libosmscout database from the raw data passed.

An import normally is restricted to a certain area of the world. Normally you find imports for countries or counties or bigger cities.

Take a look at the import tutorial for a description of how to do an import.

Database

The import tool creates a custom database from the import data. The database consists of a number of files. Some files hold data, other files act as index into data and still other files have index and actual data combined.

You can find a description of the individual database files here.

Libomsscout assumes (but does not enforce this) that all maps are stored under the same directory. Each database has its own sub directory storing the individual files.

In code each database file is accessed by an individual access class at the lowest level. These classes normally end in Index or DataFile. The Database class allows easy to all database files.

Services

To further hide the details or complexity of the low level access code, a number of Services have been defined that offer a more suitable API.

Currently the following services exist:

• MapService
• LocationService
• RoutingService
• POIService
• DescriptionService

BasemapDatabase

The basemap database is a special database that holds world wide information to be used as an background to the actual data from individual database instances.

The basemap currently holds the following information:

• World-wide coastlines

Rendering backend

For actual drawing of maps you need a rendering backend. Since libosmscout is layerd and modular the actual rendering is decoupled from database access. Services (in this case `MapService') are designed to be used by different backends. No special API is enforced.

The following backends currently exist:

• libagg backend
• cairo backend (with and without pango support)
• Qt backend
• iOS and Mac OS backend
• DirectX backend (proof of concept)
• SVG backend
• OpenGL backend (current in proof of concept, basic functionality was written as part of the GSoC 2017).
• GDI+ backend (proof of concept)

You can find more information regarding requirements for a backend here. A description of the actual render process can be found here.

Type configration file (*.ost)

The type configuration file maps certain tags onto types. Each object imported from the import fil(s) will hav a certain type.

Types are later on used to assign further information to the object and are used as a filter criteria for the style sheet.

You can find more information regarding type configuration here

Style sheets (*.oss)

To allow configurable rendering and things like night mode libosmscout uses style sheets for configuraion of the actual rendering look.

You can find more information regarding style sheets here