Datasets

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A street network is the basic source for the routing. Generally the requirements are quite simple:

 

Polylines drawn from one one intersection to the next, with optional information about oneways, name of the road, speed limits etc.

 

The rules are:

 

They need to snap

They need to split at intersections

The network should be plane unless there is an overpass (or use Z-levels, see below)

You should avoid subnets (islands)

You should avoid very long links, which have a negative impact on speed of certain calculations

 

Z-levels

 

These can be used to express the Z-level of start and end of a link, to make sure vehicles do not "jump" off bridges.

It is a value in the range -9 to 9, with 0 being used for ground level.

Many datasets use these: TomTom, HERE, ITN etc.

 

OpenStreetMap do not use Z-levels, the exception being our sample dataset, where it has been added for illustration.

 

Coordinates

 

Two kind of coordinate units are supported:

 

Spheric / Latitude-longitude (global / local)

Cartesian / Projected (local)

 

When working with spheric coordinates, all distance calculations are performed using great circle distances and the Earth is considered a perfect sphere with radius 6378.13 km.

 

When working with Cartesian coordinates, all distance calculations are performed using straight Pythagoras formula. Several different Cartesian units are supported.

 

Global projections such as Web Mercator and more are not supported. They use meters as coordinate unit, but the scale factor depends upon the latitude.

If you use it, you will not get any error messages, but the lengths will come out wrong, when you are not on Equator.