# Introduction#

A Sumo simulation network uses multiple coordination system

- x,y,z: coordinates in meters (Cartesian coordinates)
- lon,lat,z: geo-coordinates + elevation in meters (typically WGS84) if the network is geo-referenced
- edgeID, laneIndex, lanePosition: The lanePosition is the driving distance from the start of the edge (road) in meters

For the simulation behavior of the vehicles, only coordinate system 3 is used whereas the other systems are for visualization and output.

# Length-Geometry-mismatch#

By default, the length of a straight edge corresponds to the euclidean distance between its start and end positions (x,y).

However, lenghts of edges and lanes can be different from the euclidean
distance (referred to as a **length-geometry-mismtach**) are there are several reasons why this occurs.

sumo-gui and netedit can be configured to color lanes by ''by given length/geometrical length'' which highlights the mismatch between both distance values.

## Lane curvature#

By design, all lanes of an edge are assigned the same length value (corresponding to driving distance and maximum lanePosition). For curved edges, this introduces a mismatch between geometrical length and driving distance because outer lanes in a curve are longer than inner lanes.

## No-internal-links (meso)#

When running a simulation with option **--no-internal-links** or **--mesosim**
(which implies **--no-internal-links**) then vehicles will "jump" accross
intersections.
This discontinuity obviously introduces a mismatch between driving distance and
x,y coordinates.

When the network was built with netconvert option **--no-internal-links** then all edges in the network are made artificially longer to ensure that the total driving distance through the network matches the euclidean distance (averaged over the whole route). As a consequence, each edge has a length-geometry mismatch

## Abstract networks#

In some types of simulation it is beneficial to define edges with length-geometry-mismatch. For example, railway networks with switches and parallel tracks are much easier to understand when the geometrical lengths are reduced. To keep the driving-lengths at their realistic values, each edge is given a custom length value the mismatch.

# Vehicle lengths in sumo-gui#

By default, vehicle lengths are not affected by length-geometry-mismatch. This means, vehicles may seem to violate minimum gaps or even collide if they are driving on an edge where the (driving) length is longer than the geometrical (euclidean) length.