Reconstruction of “Next-generation” 3D Digital Road Model By Using Air-borne Three Line Scanner Imagery
1. INTRODUCTION
1.1 Background
Nowadays, for digital map, new demands emerge that cannot be fulfilled by traditional digital
maps, especially in many fields like ITS, pedestrian support system and so on. For example, in
Advanced Cruise-Assist Highway System (AHS, One of key issues of ITS), the typical services
should be “Support for prevention of collisions with forward obstacles”, “Support for prevention
of collisions with pedestrians crossing streets”, “Support for prevention of lane departure”
and so on.
Actually, an integration of real-time sensing and map reference from vehicles would be very
effective to achieve a complete Cruise-Assist system such as what can make driver avoid traffic
accident. However, existing digital road maps such as network data or simple 3D data for
vehicle navigation cannot support Cruise-Assist well, in particular, in urban area. It needs more
detailed shape information and more accuracy position information of Road Feature (Like Zebra,
Lane Line, and Boundary), which can make driver avoid traffic accident through Cruise-Assist
system. So method for developing the higher precision and more detailed 3D digital road map
have become issues of significant interest and high importance.
As a background of this research, it is necessary to review the related researches. The existing
approaches of building digital map from image cover a wide variety of strategies, and different
resolution aerial or satellite images. Knowledge based on image analysis for road constructing
has been developed by Zhang 2001; Automatic methods usually extract reliable hypotheses for
road segments through edge and line detection and then establish connections between road
segments to form road networks; Automatic method based on actual and complex contextual
road model.
But all of existing approaches focus on data acquisition or data update for GIS, but none of them
can meet demand of the Map mentioned above, because of limit in image resolution they used,
and difference of data use. In this paper, we are focusing on extracting High-precision 3D
Digital Road Map for ITS using, which need data with high precision and high accuracy.
1.2 Objectives
Based on this urgent demand of new high-precision road map, this research carries out a study
on how to develop this kind of high-precision road map efficiently and economically. As we all
know, photogrammetry is one powerful tool for reconstruct digital city model, but resolution
and precision of traditional aerial image is limited, which cannot satisfy so accuracy road map
reconstruction. But fortunately, a new and revolutionary air-borne remote sensor have been
developed, which is Three Line Scanner (TLS). TLS is composed of three linear CCD arranged
in parallel, and it can acquire three images of each direction (forward, nadir and backward) at
the same time, and it have high image resolution (ground resolution about 3cm) and high
position precision (about 10cm).
In this research, the author try to reconstruct the higher precision and more detailed 3D digital
road (we call it as “Next-generation 3D Digital Road Map”, NDR Map) using the above
mentioned high-resolution Three Line
Scanner (TLS) imagery. A robust road feature extraction schemes from TLS Imagery, as well as
a novel method for Reconstruction of high-precision 3D digital road map are presented.
1.3 TLS
TLS (Three Line Scanner) is an optical sensor for aerial survey. TLS is composed of three linear
CCD arranged in parallel, and it can acquire three images
of each direction (forward, nadir and backward) at the
same time. Orienting it on an aircraft perpendicularly to
flight direction, and scanning a ground plane, a triple
stereo image of a ground object can be acquired (See
Figure 1). As a result, occlusion area can be extremely
reduced. Using two images of the three, it is also possible
to get 3D coordinates by stereo matching.
Because of its principle of data acquisition, it have the
following advantages: (1) high resolution digital image can
be collected with longer CCD linear sensor by push-broom
mode; (2) seamless image strips for linear ground objects
without mosaic processing; (3) the same ground area is covered three times by push broom
mode with 100% coverage; (4) precise geometric positioning by modern GPS technology and
simple aerial triangulation with few GCPs; (5) last but not least it have low cost of data
acquisition.
Figure 1. TLS data acquisition
