11.4 Lane offset

A lane offset may be used to shift the center lane away from the road reference line. This makes it easier to model local lateral shifts of lanes on roads, for example for left turn lanes.

A combination of lane offset and shape definition can lead to inconsistencies depending on the interpolation used for the lane offset. Because linear interpolation is used for the road shape along the road reference line, linear interpolation should also be used for the offset definition to enable consistent combined use of both definitions.

img
Figure 63. Lane offset

Figure 63 shows the offset of the center lane away from the road reference line.

Elements in UML model

<laneOffset> element

In ASAM OpenDRIVE, a lane offset is represented by a <laneOffset> element within the <lanes> element.

UML class: t_road_lanes_laneOffset
XML tag:   <laneOffset> (Multiplicity: 0..*)

Lane offsets shift the center lane away from the road reference line.

Table 38. Attributes of the <laneOffset> element
Name Type Use Unit Description

a

double

required

m

Polynom parameter a, offset at @s (ds=0)

b

double

required

1

Polynom parameter b

c

double

required

1/m

Polynom parameter c

d

double

required

1/m²

Polynom parameter d

s

t_grEqZero

required

m

s-coordinate of start position

XML example

<lanes>
     <laneOffset s="25.0" a="0.0" b="0.0" c="3.9e-03" d="-5.2e-05"/>
     <laneOffset s="75.0" a="3.25" b="0.0" c="0.0" d="0.0"/>
     …
</lanes>

Calculation

The offset at a given point is calculated with the following polynomial function of the third order:

offset (ds) = a + b*ds + c*ds² + d*ds³

where

offset

is the lateral offset at a given position

a, b, c, d

are the coefficients

ds

is the distance along the road reference line between the start of a new lane offset element and the given position

ds restarts at zero for each element. The absolute position of an offset value is calculated as follows:

s = sstart + ds

where

s

is the absolute position in the road reference line coordinate system

sstart

is the start position of the element in the reference line coordinate system

A new lane offset element is required each time the polynomial function changes.

Rules

The following rules apply to lane offsets:

  • A new lane offset shall start when the underlying polynomial function changes.

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