Y
tudy, and
| need to
ing of the
1g partner
with such
refore the
Ip-to-date
'sign and
atisfy the
itySphere
Ss satellite
CitySphere images are high-resolution images acquired by
QuickBird satellite; they were introduced by DigitalGlobe to
provide surveyors, city planners, and geographic information
systems specialists with a comprehensive, current, and
repeatable image data covering major cities. These images
provide the foundation and geographic context for a wide range
of applications that require an up-to-date imagery; they are
ideally suited for applications requiring consistent, reliable, and
current data coverage of study sites where there is a need to
integrate imagery into the workflows and decision-making
processes.
CitySphere images used in this project are a collection of colour
image mosaics acquired over Tripoli city in and around March
2006, these mosaics were arranged, co-registered, and projected
resulting in an ortho photograph mosaics. The resolution of
satellite imagery is 60 cm, projected according to the WGS-84
datum system where the 33" zone of the Universal Transverse
Mercator projection (UTM) was used. The individual image
mosaics were aligned together to cover the whole area of Tripoli
city, and put into GeoTiff image format which is very much
suitable for computer aided design and geographic information
systems related applications. Software used in processing these
images included AutoCAD, GIS, and image processing
programs.
To cover all areas where the Metro network is planned, the
above mentioned image was complemented by a separate
satellite image covering narrow path extending from the borders
of the city to Tripoli International Airport and centered on the
axis of the Airport highway which is aligned with the planned
(B) Metro line. This last ordered image was acquired on March
2008 and has similar technical characteristics as the first one.
The satellite imagery has the advantage of providing coherent
and comprehensive representation of earth’s surface objects
being imaged. Regarding their content, they truthfully reflect
the facts on the ground at the time of acquiring the image
(Lillesand and Kiefer, 1979; Detrekoi et al, 1996). However, in
a city like Tripoli undergoing dynamic development and
extremely rapid changes, the facts on the ground change fast
too. Another important reason supporting the choice of satellite
imagery as a base map is that such images can easily be
modified to suite the computer assisted planning of the project,
this is achieved with an acceptable relative accuracy (Alhusain,
2007).
Unfortunately, the nominal 2.5 m horizontal accuracy provided
by the distributor of the images didn't prove to be true in all
cases, especially in real life applications. This was especially
critical issue when fitting and harmonizing some technical
aspects of this project to other similar significant development
projects executed in Tripoli. Coordinates transformations
carried out on imagery didn't bring satisfactory results, for this
reason a process of co-registration by identifying identical
points on different multi-temporal images and carrying out local
image transformations became necessary. Further significant
problem was that the satellite imagery did not contain altitude
information.
Overall, after carrying out the necessary geometric corrections,
transformations, and co-registration the ordered satellite
imagery has satisfied the required accuracy needs. By producing
the necessary orthomaps it was possible to greatly facilitate the
field work of the Metro planning teams and to support the in-
office work of Metro lines design, and imposition of Metro
stations in their suitable locations. Nonetheless, the acquired
images proved to be cost effective solution during the course of
establishing the concept of the traffic study and the decision
making process of the Metro network. At the same time satellite
imagery constitutes correct and impressive technical basis for
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
documentation and presentation of plans and technical solutions
prepared through the traffic study (Alhusain, 2007; Engedy
2008).
3. MAPS USED IN THE PLANNING STUDY REVISION
During field visits, and data collection activities of January
2008. Our company and its teams got in contact with other
experts responsible for planning and execution of similar big
development projects in Tripoli. One of the important meetings
took place between our teams and the Swedish subcontractor of
the National Consulting Bureau of Libya (NCB). The NCB and
its Swedish subcontractor are responsible for the city's future
urban development; specifically they are working on the "Third
Generation Planning Project” which envisages the urban
development of the city until the year 2025. The managers of
this project had indicated that their task, besides preparing the
development plans for the city and its surrounding region, was
to create totally new and modern technological principals
dependent base map. This base map relies on 10 cm resolution
aerial photographs acquired over Tripoli in 2008. Expert-level
meetings between our teams and the NCB's have shown that the
finished parts of the base map also constitute a useful tool
capable of supporting the demands dictated by mapping tasks of
the Revision of the Metro Planning Study. Steps were taken by
our contracting partner (RPEMB) to provide us with these
aerial photographs, the efforts of our partner were successful,
and we received the aerial photographs in August 2008, figure
5, shows an example of these photographs. Aerial photographs
serving as the basis for producing the base map were acquired
over Tripoli in autumn of 2006 and the beginnings of 2007.
Flight height was 1000 m, out of the raw aerial photographs
ortho photographs of 10 and 30 cm/pixel resolution were
produced. Photogrammetric data capturing of the aerial
photographs to produce vector maps has begun at the (NCB).
Figure 5. Aerial photograph covering one of the Metro
planning areas
The (NCB) provided our experts a 30 cm/pixel resolution ortho
photograph mosaics. According to their information, these
mosaics in their present form are not considered to be a final
