The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B6b. Beijing 2008 
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enables providing the global position determination. Once a 
user purchases a receiver, one can get the normal position 
service for free and the accuracy is good enough for many LBS 
applications like car navigation and tourism service (the 
commercial service needs payment but offers better 
performance). However these systems have drawbacks like 
urban canyon effect which make indoor navigation almost not 
possible. 
GSM cellular network also provides location service in a wide 
area through most used mobile phones indoors and outdoors. 
But users have to pay monthly or per request for the service, 
and the location accuracy is not high. Therefore, it is only 
suited for LBS applications like emergency calls to get a rough 
location extent. 
Wireless network is rapidly growing in the centralized 
downtown areas, and the location sensing technique depends on 
the software framework. No hardware except wireless card is 
necessary, which is available for most of the modem mobile 
devices. Comparing with GPS, the achieved accuracy is better 
in urban areas but worse in rural areas because the wireless 
network coverage is not wide enough in rural areas or many 
developing countries. 
Figure 2. The hybrid model of different location sensing 
techniques 
Other location sensing techniques like IR, 3D-iD RF tag and 
Active RFID can obtain very high accurate locations indoors or 
outdoors. However some drawbacks can not be easily avoided 
such as: they incur significant installation and maintenances 
costs when considering large area coverage, their performance 
may be strongly decreased by many surrounding factors like the 
weather and obstructed objects, and so on. 
Thinking over the pros and cons of the above location sensing 
approaches, it is widely accepted that fusing multiple sources of 
location sensing techniques will be the optimal solution for the 
ubiquitous LBS applications (Borriello et al., 2005). Figure 2 
shows the hybrid model that combines different techniques, e.g. 
using the GSM cellular network to acquire a general location, 
and then using wireless network or GPS to get the exact 
location can greatly improve the speed and accuracy to 
determine the user’s location. 
Although the location sensing techniques for 2D LBS and 3D 
LBS are equivalent, 3D LBS applications deal with detailed 
indoor objects and thus greatly demand high accuracy indoor 
positioning in many cases. The hybrid model allows getting 
location information through shifting among different location 
sensing techniques, e.g. GPS used in widely open areas, GSM, 
WLANs or RFID used in built-up areas. Such model has been 
carried out in the industry like the Skyhook wireless network. 
When adopting this model to future 3D LBS, three factors 
including accuracy, coverage and cost should be the dominant 
determination to combine different location sensing techniques. 
2.3 Wireless Networking: 
For LBS mobile devices, basically there are two main 
approaches for transferring the data from server to client. The 
first one is using the protocols of the cellular network. From so 
called the second generation (2G) GSM network, to 2.5G 
GPRS/EDGE, to 3G UMTS network, LBS span these mobile 
telephony technologies. As the development of new generation 
of mobile network, data transferring speed is increasing from 
theoretically 171.2 Kbps (GPRS, internet based) to lGbps (IMT 
Advanced). The second one is the wireless LAN network 
(WLAN), whose data rate varies in the range of 1 to above 
100Mbps using 802.1 lx standards. 
Ma et al. analyzed both approaches and concluded that: cellular 
networks provide always-on connectivity in large area with 
relatively low data rates to users with high mobility; WLANs 
give much higher data rates to users with low mobility over 
local areas. Then they investigated a hybrid method to 
seamlessly integrate both approaches using the Stream Control 
Transmission Protocol for getting better data transferring 
performance (Ma et al., 2004). Obviously, 3D LBS using large 
amount of datasets require more bandwidth and fast data 
transferring techniques. 
2.4 Data standards 
There are many standards for 2D and 3D data in the GIS world. 
Normally, 3D data standards allow defining 2D data as well. As 
stated by Kolbe et al. (Kolbe et al., 2005), semantic and spatial 
interoperability are two vital principles for defining a useful 3D 
city model in GIS. Thus, we introduce several well known 3D 
data standards and figure out their different characteristics 
based on the semantic and spatial aspects. 
VRML/X3D: are computer graphics standards (X3D is the 
successor of VRML97) that provide only the possibilities to 
describe the geometric structure of 3D objects. They do not 
have the support for the representation of thematic information. 
For example, you could not find out the meaning of an object or 
aggregate objects (e.g. a building), their attributes or 
relationships with other objects. Thus, it is very hard to perform 
complex 3D spatial analysis. 
LandXML/LandGML: is a specialized XML/GML standard 
for civil engineering, land management, surveying and cadastre, 
used in the land development, transportation and pipe networks. 
However, it does not support complex 3D geometry types like 
volumes, but only represent 3D objects via their footprints. 
Keyhole Markup Language (KML): is an XML-based 
language schema for expressing geographic annotation and 
visualization in the web. It has been widely used in the GIS 
community and recently approved as an OGC standard. 
However, for describing 3D objects it has similar shortcomings 
as VRML/X3D.