Honda Odyssey Service Manual: LaneWatch   System

LaneWatch may reduce the driver's blind spot by capturing the image by the LaneWatch camera mounted under the passenger's power mirror. The image is displayed on the center display when the turn signal is activated to the passenger's side or the LaneWatch switch is pressed.

Reference line

The LaneWatch image is provided with the three reference lines, each line shows the distance from the rear bumper.
Three lines that appear on the center display can give an idea of how far the vehicles or objects on the center display are from your vehicle, respectively. If an object is near line 1 (in red), it indicates that it is close to your vehicle whereas an object near line 3 farther away.