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Figure 1. Vision-based road infrastructure management —
typical focal points and objects of interest.
1.3 Goals and structure of this paper
The paper aims at demonstrating the practical feasibility of an
interactive and accurate 3d geoinformation environment for
road infrastructure management relying entirely on multiray and
stereo imagery (and on their derivatives such as fully textured
3d point clouds). The main purpose of the investigations was to
identify the typical requirements, the technical and operational
challenges in establishing and exploiting such an environment
and the limitations of the approach.
First we introduce our proposed solution of an interactive 3d
information environment integrating high-resolution ground-
based multi-stereo imagery with high-resolution airborne
imagery. We then identify the main challenges and requirements
to be met by such an integrated solution through all process
phases — from the image acquisition and 3d information extrac-
tion to the cloud-based exploitation. We then introduce techno-
logies for the acquisition and processing of the ground-based
and airborne imagery and for their subsequent integration. In
the following section of the paper the concept and the
technologies are applied to and evaluated in a highway mapping
project in Switzerland. The paper is concluded with first results
and a discussion of future work and challenges.
2. PROPOSED IMAGE-BASED 3D GEOINFOR-
MATION ENVIRONMENT AND WORKFLOW
2.1 Overview
We propose a seamless image-based 3d visualisation and 3d
measuring space integrating very high-resolution airborne
imagery and mobile multi-stereo imagery. The solution employs
airborne 3d views and terrestrial 3d views and complements
these views with dense, fully textured 3d point clouds derived
from the airborne and ground-based imagery. This combination
of 3d views and 3d point clouds provides a permanently three-
dimensional visualisation and measurement space and permits
seamless transitions between airborne and ground-based 3d
views via freely navigable 3d point clouds.
Thus, the solution offers a number of horizontal and vertical
viewing perspectives with accurate 3d measurement capabilities
either by means of stereoscopic digitising or by 3d
monoplotting. The incorporation of dense 3d point clouds
which are derived from the identical imagery and which
therefore possess perfectly co-registered RGB or even RGB &
NIR texture provides a number of potential benefits over
exclusively image-based 3d models. For example, it enables the
inclusion of dense road surface models or the direct extraction
of road profiles and their inspection within the 3d visualisation
environment. It furthermore frees users from the original
viewing geometries and adds a greater freedom of navigation
within the 3d environment.
2.2 Challenges and requirements
In order to obtain such a dense, accurate and interactive image-
based 3d visualisation and 3d measurement space the following
major challenges and requirements have to be met:
e Acquisition — Provision of a very high-resolution coverage
of the road surface itself with a GSD € 1 cm and a high-
resolution coverage of the entire road corridor, including
100-200 metres on either side of the road axis, with a GSD
ofz5 cm.
e Georeferencing / Co-Registration — Accurate georeferen-
cing and in particular highly accurate co-registration of
airborne and terrestrial imagery — leading to accurately co-
registered derived 3d data.
e Extraction — Automatic extraction of dense depth informa-
tion — and subsequently 3d point clouds — from the airborne
and terrestrial imagery respectively. The dense depth
information is to support accurate 3d monoplotting and
object extraction in image space on the one hand and a
greater freedom of user navigation within the geospatial 3d
environment on the other.
e Integration and Exploitation — All the above mentioned
geospatial data, i.e. georeferenced airborne and terrestrial
stereo imagery, 3d point clouds, as well as derived products
such as orthoimagery, DSM and 3d objects need to be inte-
grated into a suitable 3d software environment permitting
the interactive exploitation of the rich 3d road scene.
The following three technologies are subsequently used to
demonstrate and validate the proposed integrated airborne and
terrestrial image-based 3d road infrastructure management
approach:
e ground-based image acquisition and processing: IVGI
stereovision mobile mapping system and stereovision
processing and exploitation software
e airborne image acquisition and processing: Leica RCD30
and Leica FramePro
e integration and exploitation: OpenWebGlobe 3d virtual
globe technology
3. GROUND-BASED IMAGERY: ACQUISITION AND
PROCESSING TECHNOLOGIES
3.1 Stereovision based mobile mapping system
For our research we use the IVGI stereovision mobile mapping
system which is being developed since 2009 as part of the
SmartMobileMapping research project. The system was
originally intended for road sign management and has since
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