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.
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.
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.
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
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.