### Road graph plugin settings

Road graph is a C++ plugin for QGIS, that calculates the shortest path between two points on any polyline layer and plots this path over the road network.

Plugin units
Topology tolerance
Transport layer settings

#### Plugin units

You can adjust the units of the calculated distance and time of the path. Select the units in Distance unit and Time unit.

#### Topology tolerance

Topology tolerance - the distance in units of the project. If the distance of two points falls short the topological tolerance, they are considered to be the vertex. A topological tolerance value greater than zero slows down the plugin, but you can use not ideal data sources.

##### Note

The Road graph plugin considers two roads as linked, if they have a common node. A Node is uniquely identified by it's coordinates. However, in the process of digitizing errors may occur. The errors sometimes occur when the network is transformed from one coordinate reference system to another. This might cause the Road graph plugin to consider connected roads as disconnected. In that case the topological tolerance should be set to a value greater than zero.

#### Transport layer settings

Layer - the data layer of roads.

Field direction - the value of this field indicates how to interpret the Road graph plugin layers feature. Value for forward direction - the direction of movement corresponds to the order of points in a feature. Value for reverse direction - the direction of movement corresponds to the reverse order of points in the feature. Value for two-way direction - both possible.

Speed field

- field containing the recorded speed on the road.

##### Default settings

If the attribute table of your linear layer does not contain the required fields or fields contain unexpected values, the plugin will use default values. You can set them in the default tab Default settings.