Peer-Reviewed Articles
377 On Improving Navigation Accuracy of GPS/INSSystems
Dorota Grejner-Brzezinska, Charles Toth, and Yudan Yi
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Direct georeferencing, also referred to as direct platform
orientation (DPO), is defined as direct measurement of the
imaging sensor external orientation parameters (EOP), using
positioning and orientation sensors, such as the Global
Positioning System (GPS) and Inertial Navigation System
(INS) or Inertial Measurement Unit (IMU). Imaging sensors,
most frequently supported by the DPO technique, are digital
cameras, lidar systems, multi-spectral or hyper-spectral
scanners, or interferometric synthetic aperture radar (INSAR).
While for scanning sensors the use of DPO is compulsory,
frame digital cameras can also directly benefit from this
modern technique of sensor orientation. With direct sensor
orientation, the requirement for ground control, tie-point
matching and aerotriangulation (AT) is significantly reduced,
or even entirely eliminated, resulting in shorter times of data
acquisition and processing, and streamlined and highly
automated data workflow and quality control. Most of the
time, the requirement for ground control points is limited
to periodic system calibrations and quality control check.
Direct georeferencing is considered a fundamental technol-
ogy of conventional mobile mapping systems (MMS).
Despite significant progress in GSP/INS-based direct geo-
referencing technology in the last decade, there is still room
for improvement in terms of better accuracy and better tolerance to GPS outages.
This paper is focused on three error
modeling and compensation techniques that could potentially
improve GPS/INS system’s performance on both land-based and
airborne platforms: (1) extended gravity compensation, (2) IMU
signal de-noising, and (3) stochastic modeling of IMU errors.
391 A Fully Integrated Solution for Aerial Surveys:
Design, Development, and Performance Analysis
Mohamed M.R. Mostafa and Joe Hutton
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The focus of this paper is to present the current technological development
in the field of system integration for data
acquisition and georeferencing for aerial survey applications.
The presentation is solely based on a commercial fully
integrated system, the Digital Sensor System (DSS). The DSS
is a fully-integrated, fully digital ruggedized system for
airborne image acquisition, georeferencing, and map production. The DSS consists
of a 4K x 4K digital camera, a GPS-aided INS direct georeferencing system,
and a flight management system. The DSS software suite interfaces seamlessly
with commercial off-the-shelf photogrammetric software
allowing for fast topographic and orthophoto map production. The DSS currently
uses a CCD chip with a 9 µm pixel
size which allows digital image acquisition with a ground
sample distance that ranges from 0.05 m to 1.0 m using
its 35 mm and 55 mm lenses. The embedded POS AV direct
georeferencing system provides the exterior orientation
parameters in both real-time and post-mission modes. The
DSS is used primarily to generate high-resolution color
and color infrared digital orthophotos, orthomosaics, and
topographic maps which can be used for many different
mapping, GIS, and remote sensing applications.
399 Airborne Non-metric Video Image Orientation
Determination Using Two GPS Receivers
Gilad Even-Tzur, Uzi Ethrog and Amir Bar-Maor
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In theory, using a GPS system in conjunction with an Inertial Measurement Unit
(IMU) enables photogrammetric
mapping even without using ground control points. But
such systems are expensive, not highly accessible, and
not suited for close range photogrammetric measurements
based on airborne video photography. This paper presents
an alternative modified system which enables setting the
position and attitude of video images acquired from a
helicopter. It is a fairly simple system comprised of an
analogical video camera and two kinematic GPS rover
receivers. One GPS antenna is located close to the camera
and used to locate the camera at the time of the image
acquisition. The second antenna is suspended underneath
the helicopter. It functions as a flown control point and
appears in all the video images. Thus, a photogrammetric
model or strip is created in which the coordinates of the
exposure point and of one of its image points are always
known in all the photographs. The solution process for such
a photogrammetric model or strip is presented, as well as,
the results and accuracy of the experiments that were
carried out to test the system.
405 Real-time Speed Limit Sign Recognition Based
on Locally Adaptive Thresholding and Depth-First-Search
Jianping Wu and Yichang (James) Tsai
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Stop signs and speed limit signs (SLS) are the most popular
and significant traffic signs on roadways. Unlike extracting
stop signs with a distinct red color, extracting SLS in a real-time environment
is much more challenging. This paper
presents an algorithm for recognizing SLS from video imaging and extracting
the numerical numbers of SLS to support
real-time road inventory data collection operations. The
algorithm consists of color segmentation based on locally
adaptive thresholding extraction of regions of interest (ROI)
using a depth-first-search algorithm, followed by speed limit
sign detection and speed limit number extraction by means
of optical character recognition and 2D correlation. The
algorithm was implemented in Visual C++ language and
tested on a non-Hyper-Threading Pentium IV PC with 3.06GHZ
CPU using the images taken in the field with different image
sizes. The average processing time for an image of 1200 x
800 pixels is about 125 ms. Experimental results from 1,401
video images show 0 percent false positives out of 1,278
images containing no SLS, and 3 percent false negatives out
of 123 images containing SLS.
415 Updating A Digital Geographic Database using
Vehicle-borne Laser Scanners and Line Cameras
Huijing Zhao and Ryosuke Shibasaki
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The Vehicle-borne Laser Measurement System (VLMS) is a
mobile mapping system where three single-row laser range
scanners, six line CCD cameras, and a GPS/INS-based navigation unit are mounted
on a van to measure object geometry
and texture along a street. This paper contributes to a method
of fusing the data output of VLMS with existing geographic
data sources where the focus is on the rectification of the
vehicle’s motion data derived from GPS/INS, which may be
quite erroneous in an urban area. An algorithm is developed
to correct the four variables of the vehicle’s motion data,
i.e., x, y, and z coordinates of the vehicle position and yaw
angle of orientation by registering the laser points of the
VLMS with an existing data source, e.g., a DSM. The algorithm
was examined using the VLMS data that were taken in the
Ginza District, Tokyo. By manually assigning 18 sets of tie-points, the vehicle’s
motion data were corrected automatically and efficiently, such that the laser
points of VLMS were
matched to a DSM. In data fusion, a set of objects, which
contained commercial signboards, traffic signs and signals,
road boundaries, and road lights were extracted from the
corrected VLMS data using an interface described in a previous paper. They
were integrated with a 1:2500 3D map
that consists of only building frames. In addition, line images
from the VLMS were projected onto the building facades of
the 3D map, and textures were generated automatically.
425 Hierarchical Recovery of Digital Terrain
Models from Single and Multiple Return Lidar Data
Yong Hu and C. Vincent Tao
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A hierarchical terrain recovery approach for generating
digital terrain models (DTM) from single and multiple returns
lidar data is presented in this paper. The algorithm can
intelligently discriminate between terrain and non-terrain
points by using adaptive and robust filtering and interpolation techniques.
It processes the image pyramid, bottom-up
and top-down, to estimate high-quality terrain surfaces from
lidar data with varying point densities and scene complexities. Using road
and vegetation information, the algorithm is
able to adaptively adjust thresholds to be suited to process
changing contents in a large scene. The algorithms have
been tested extensively using multiple medium - and high -
resolution lidar datasets. The worst-case error is below 25 cm
Linear Error (LE) 90 comparing the derived DTMs and the raw
range images on bare surfaces when testing several lidar
datasets.
435 Small-Format Digital Imaging for Informal
Settlement Mapping
Jonathan Li, Yu Li, Michael A. Chapman, and Heinz Rüther
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Recent advances in technology and wider commercial applications have promoted
the remote sensing and airborne
mapping communities to take a closer look at digital imaging
and its advantages over conventional film-based, large-format
aerial photography. In this paper, we focus on the potential
of high-resolution, digital color imagery acquired from an
airborne small-format digital camera for rapid mapping of
complex urban informal settlements. We discuss the example
of automated building extraction using a novel color edge
extractor developed with similarity-based color morphology
and report on investigations into the use of this low-cost
digital imaging option for rapid spatial data acquisition of
informal settlements under dynamic conditions. Results from
our work suggest that the approach taking advantage of color
information to generate attributed edges to hypothesize shack
roof outlines by exploiting the fuzzy similarity measure and
color morphology is a potential new avenue to automatically
extract buildings from high-resolution color digital imagery.
443 Mobile GIS with Enhanced Performance for
Pavement Distress Data Collection and Management
Bo Huang, Chenglin Xie, and Hongga Li
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In recent years, there has been a significant shift in the
development of a Geographic Information System (GIS) from
desktop applications to mobile field applications. By
integrating the precision location data collection capability
of Global Positioning System (GPS) and the spatial processing power of GIS,
mobile GIS provides an ideal basis of
building systems for field workers to collect data with
increased efficiency and ease. This paper presents the
design and implementation of a pavement distress data
collection and management system for efficient airport
pavement condition inspection with the aid of mobile GIS.
The system seeks to streamline the field data collection
process by offering a customized user interface for distress
data entry, transformation, retrieval, and real-time transmission through wireless
handheld devices. An R*-tree algorithm has been explored to index the distress
data and
speed up the retrieval of distress information when performing spatial and
attribute searches. A least squares adjustment algorithm is also introduced
in an effort to improve
the precision of GPS data. Furthermore, a wireless communication algorithm
has been developed to enable the transmission of distress data from the mobile
client in the field to
the in-house GIS server. On the side of hardware, Pocket PC
has been chosen as the platform for deploying all field
operations. Three peripheral devices, namely the GPS
receiver, digital camera and wireless card, are attached to
the Pocket PC for capturing distress location, digital photos
and support wireless communication, respectively. The
effectiveness and efficiency of the system have been tested
and verified by various field trials in Singapore Changi
International Airport.
453 Integration of Mobile GIS and Wireless Technology
for Coastal Management and Decision-Making
Xutong Niu, Ruijin Ma, Tarig Ali, and Rongxing Li
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Geographic Information Systems (GIS) have become a crucial
support tool for governmental decision makers at many
levels. Internet-based GIS applications provide unique services for the presentation
of spatial data and mapping
products to a broad range of audiences. Furthermore, compact and portable mapping
devices provide new opportunities for the expansion of Internet-based GIS applications.
In
this paper, we present results of the research and development of a web-based,
mobile, spatial system for coastal
management, and decision-making that integrates these
technologies. The developed system consists of an on-site
mobile spatial subsystem, a web-based shoreline erosion
awareness subsystem, and a coastal structures permit
subsystem. The system is designed and developed for
applications in the Lake Erie area and has the potential to
be adapted and applied in other coastal areas.
461 The Development and Testing of a Prototype
Mobile Mapping System for Real-time Forest Fire Hot Spot Detection
Naser El-Sheimy and Bruce Wright
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The development of a mobile mapping system (MMS) to
test the feasibility of automatic real-time identification and
location of forest fire hot spots is discussed in this paper.
The system combines an integrated inertial navigation system (INS) and Wide
Area Differential Global Positioning
System (WADGPS) with a thermal video imager and computer
system. The overall objective of the system is to achieve an
overall positioning accuracy of 2 m or better in real-time for
the location of forest fire hot spots.
The direct georeferencing model used in this system is
briefly presented as well as how it is partitioned for implementing the real-time
georeferencing of the thermal images
and the final hot spot georeferencing. The paper then presents some specific
issues affecting the identification, extraction, and tracking of forest fire
hot spots from thermal images.
Some of the hardware and software issues considered in
designing the overall process flow for implementation as a
real-time system are discussed next. Finally, an evaluation
of the system’s potential real-time operation and georeferencing accuracy
is presented.