Keywords: TLS (three line scanner), air-borne sensor, ITS, object tracking
Abstract: Acquiring traffic data such as number of cars, speed distribution, number of illegal
parking cars accurately and quickly is needed for ITS (Intelligent Transport System). ITS is
expected to mitigate traffic jam and to improve management of limited road resources. Currently,
as a common practice, only limited traffic data are collected; vehicles are counted using roadside
ultra-sonic sensors. Finding traffic accidents depends on the witness’s notice, patrol of road
administrative officers, and monitoring with roadside cameras. TLS (Three Line Scanner) is an
air-borne sensor consisting of three parallel one-dimensional CCDs mounted on the imaging
plane. It obtains seamless high-resolution images (5-10cm on the ground) with three viewing
directions (fore, nadir, aft) simultaneously mainly to generate 3D spatial data accurately. In
addition, the high-resolution imagery can be applied to observe running cars, speed and parking
cars on the street since TLS scans the same road surface with a time interval with approximately
10 seconds. This paper describes methodologies and the results of applying TLS imagery to the
tracking of automobiles.
1. Introduction
ITS (Intelligent Transport System) society will spread in near the future. ITS is expected to
operate traffic flows and to provide efficient road administration. But generally, acquiring traffic
data depends on roadside ultra-sonic detectors, cameras, witness’s notices or patrols of road
administrative officers. Traffic data acquired with such devices are basically point-based and fail
to represent spatial distribution. It is quite necessary to develop a method of acquiring traffic data
such as number of cars, speed distribution, finding accidental vehicles accurately and quickly
over large areas. The high-resolution imagery of TLS (Three Line Scanners) can be applied to the
observation of running cars, their speed and parking cars on the street because TLS can scan the
same road surface and objects with a time interval with approximately 10 seconds.
2. TLS system
2.1 TLS principle
TLS (Three Line Scanner) is an air-borne sensor consisting of three parallel one-dimensional
CCDs mounted on the imaging plane (Fig.1 and Fig.2). It obtains seamless high-resolution
images (5-10cm on the ground) with three viewing directions (fore, nadir, aft) simultaneously
mainly to generate 3D spatial data accurately with RTK-GPS and INS.
Fig.1: Method of TLS image Acquiring
Fig.2: Plain TLS image
2.2 TLS performance
Table1: system specification of TLS
| CCD |
Number of pixel/line |
10200 pixels |
| Pitch of pixel |
7 um |
| Number of CCD |
|
3(monochrome), 1(RGB) |
| Number of shading |
|
12 bit |
| Lens |
Distance of focus |
60mm |
| Angle of stereo |
|
21° |
| Frequency |
|
500 line/second |
2.3 TLS characteristics
Characteristics of TLS are summarized as follows.
- Seamless high-resolution images (5-10cm on the ground, about aerial photograph class) can
be obtained with three different viewing directions (fore, nadir, aft). Easy to create
ortho-image from TLS images because TLS images are “line-projection” and less distorted
than conventional aerial photo-images, which is point-projection image.
- Much less ground control point is needed since RTK-GPS and INS can estimate the sensor
position and attitude accurately.
- TLS system records digital data directly, which enable users to easily process and analyze
them on the real-time basis and help minimize processing errors.
- Multi-spectrum images can be acquired by replacing the filters and sensors.
