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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
similarity with the image seen by the human eye. Changes in 
elevation are clearer as contour lines and spot heights need not be 
interpreted.  Intervisibility can be assessed and more detailed 
surface information can be displayed, such as entrances to 
buildings and height of windows. The ability to fly around 
objects in real time offers the opportunity for increased situational 
awareness. 
However, a potential disadvantage of using a 3D model is that it 
may not be realistic, surface colours and textures may have to be 
inferred, vegetation, such as trees, have to be representative from 
a limited library. The speed of production must be considered 
since detailed 3D models can take a significant time to generate, 
as well as the amount of extrapolation, such as assuming the rear 
of a building to be the same as the front. As with 2D maps, issues 
such as currency and ensuring the models are up-to-date still 
apply. Issues of how to serve 3D and VR data need to be 
explored. One option is to use web servers to allow distributed, 
secure and fast access to large centrally held 3D models over a 
network. New technologies are being developed that allow users 
to access an image of the models without having to download 
terabytes of data. The type of viewer used by the end user also 
needs to be considered, with issues cost, ease of use, maintenance 
and functionality to be considered. 
In parallel with developments in 3D modelling and visualisation, 
there have also been significant developments in sensing systems 
that can rapidly collect the 3D data required to generate urban 
models. Techniques such as rapid capture with terrestrial laser 
scanning have allowed large datasets to be collected within a 
small time-scale and this does not require excessive processing 
time in order to produce models. On a larger scale, airborne 
LIDAR can be used to collect data over a city at good accuracies 
and resolution. These laser surveying systems are routinely used 
to generate 3D models for civil engineering projects. 
2. METHODOLOGY 
To investigate these issues and relevant technology developments 
in the creation, exploitation and visualisation of 3D urban models, 
a study was recently performed on Rapid 3D Urban Modelling. 
The project initially performed an assessment of the end user 
community for 3D urban data and defined their information 
requirements. This was completed by targeted visits to 
organisations such as the Defence Geographic Centre (DGC) and 
Geographic Engineering Group (GEG). Questionnaires were 
used to obtain product specifications such as scale, coverage, 
feature set and timeliness issues. It was important to define the 
level of information required by the user, whether it be a basic 
Digital Terrain Model (DTM) or a detailed 3D model and the time 
frame of requirement. The visualisation level was also 
considered, from full scene rendering with illumination effects or 
just simplified objects. Production capability was also assessed 
such as data sources, timeliness and software used. 
The next task was to determine the government sponsors of work 
in this field and to capture their main objectives. This was 
achieved by personal communication with research co-ordinators 
and evaluation of tasking orders. 
A review was then undertaken of software tools that could be 
used to generate, render and visualise 3D urban data, covering 
both commercial software packages and academic research 
developments. Information is a key part in providing 3D urban 
data and therefore the next step was to provide an overview of the 
available information sources that can be exploited. 
3. OUTCOME OF STUDY 
The study found that there were numerous users of urban data 
within the defence community. Homeland defence activities are 
very rapid as information is often required urgently. Presently, 
Ordnance Survey (OS) data and military mapping data is used 
alongside survey data from total stations. Recently, terrestrial 
laser scanning was being tested for future implementation as it 
offers the opportunity for rapid data capture from longer ranges, a 
major advantage in anti-terror operations. 
It has been suggested that 3D models of high-risk areas could be 
created and stored for future use. Sites of high security value and 
high risk public events in London, for example, require security 
reviews, frequent contingency planning and constant updating in 
the light of new requirements or changes to the environment. The 
ability to walk through and view the area in different conditions 
could save recurring costs of survey visits. Changes to physical 
security measures such as fences, barriers, lighting and patrol 
frequency can be modelled easily. The study found that there was 
a need for 3D mapping although simplified models with little 
rendering would be sufficient for many site orientation 
applications where accuracy was not a paramount requirement. 
Soldiers use 3D mapping at Brigade and Company level, with 
activities such as mission rehearsal, scene familiarisation and 
mission planning. Specific applications include route analysis, 
location of observation posts, identification of potential obstacles, 
building access, collateral damage prediction, containing and 
isolating combatant forces, creating buffer zones, restoring 
essential services, evacuation of groups of people and gathering 
information. This group requires accurate models with high 
levels of visualisation at short time scales. It would be unrealistic 
to build a model of locations to support planning of urban 
operations when time duration of operations cannot be foreseen 
beyond a few weeks. However, for urban areas where a long time 
presence is expected, or where operations might be expected to 
recur over a period of time, the development of an urban model 
could be a worthwhile investment for planning and to assist in 
situational awareness. It was found that in practical terms, 
additional information would be required with the 3D model to 
achieve maximum utility. For example, building usage 
(residential, commercial, military, police), construction details 
(cladding, material, thickness) and significance (cultural, medical, 
educational, religious) would add value to a model. 
For some operations, it was found that users appreciate feature 
annotation, such as heights of window sills and simple 
presentation as there is not sufficient time to use complex