Function update_pos_indicator 

pub fn update_pos_indicator(
    pos_indicator: Single<'_, '_, (&mut TrackPos, &mut Transform), With<PositionIndicator>>,
    q_segments: Query<'_, '_, (&TrackSegment, &Transform), Without<PositionIndicator>>,
    target_segment: Res<'_, TargetSegment>,
    cursor_pos: Res<'_, CursorPos>,
)

Updates TrackPos of PositionIndicator to the current projection of the cursor position to the target segment.