Imported or manually created street networks often lack elevation data, which is necessary for the 3D display of crossing streets. The Generate Bridges tool can automatically create such data. It can by executed by clicking Graph > Generate Bridges.... in the main menu. It operates either on the current street selection or on all streets when nothing is selected.
The wider street is kept naturally at its original level, while the thinner street is raised. Also, please note that new street nodes are inserted at the correct distances from the crossing point, defined by the maximal defined slope. The vertical tangent components are automatically adjusted.
The Generate Bridges tool adds elevation data to the streets:
Generate bridges settings
Vertical distance to be set between two crossing streets. Note that the 'Ramp maximum slope' influences the resulting node elevations.
Object attribute for level (optional)
The height coordinate can be calculated from specific object attributes of streets. The height coordinate is set to "Level height" multiplied with the indicated attribute name. Attributes can either originate from imported data or be manually assigned, allowing full control of the vertical street layering.
Only apply level when streets cross
Sometimes, imported GIS data, such as OSM data, may contain faulty attribute values that cause the creation of elevated parts of streets. This option activates or deactivates the vertical alignment in regions, where actually no other streets cross the street of interest.
Object attribute for absolute height (optional)
In contrast to the object attribute for level, this attribute allows direct specification of absolute heights. When a street has this attribute, the level height is ignored.
Ramp maximum slope
Maximum slope of ramps (vertical climb per horizontal unit).
Bridge join preference
If a street contains multiple bridges in a row, they are linked together according to this value. Low values: unlikely to join, high values: always join.
Lock non-zero heights
Do not change height of nodes with non-zero position.
Allow tunnels (streets below zero height). Note that this is quite a rare state to construct. Note also that the Shadow Plane is rendered at smallest (thus negative) elevation value.
Use visible terrain
Treat all heights as relative above terrain (if any). This causes bridges to follow the terrain.