Geoscience Reference
In-Depth Information
1 Introduction
Implementation of SDIs using open standards are well discussed over the recent
years, where in three-dimensions (3D) SDIs are developed using City Geography
Mark-up Language (CityGML) (Kolbe et al.
2008
) as back-end data transfer and
implementing X3D in geometry portrayal layer. (Basanow et al.
2008
). City
models are especially important for presentation of business locations, urban
development that is required by public and private sectors, such as providing the
platform supporting from civic participation to decision-making and policy-for-
mulation extent (Kolbe et al.
2008
). The distinct feature of CityGML is that it is a
schema based on XML standard carries geometries and semantics information in
one format. XML is a popular W3C standard in data exchange and sharing usage
in computing systems due to its readable and self-describing benefits. Considering
the cost involved, transmitting 3D models in CityGML format is considered
impractical. However, dealing with semantic data requirements in analysis over
web services, compressing CityGML should be a step forward. Different work-
arounds of compression tasks could be implemented, however in this chapter the
schema-aware encoder (CitySAC) is used as a proprietor encoder and act as a
compression component in the web services.
In this chapter, the development of schema-aware encoder for CityGML and its
results compared with dictionary and arithmetic compression modules such as 7-
zip, WinZIP, InfoSet, etc. are briefly discussed, then the following section dis-
cusses the development of javascript decoder and how the retrieval process could
be done via code-on-demand in web application. The dataset that is used in this
research is 3D Putrajaya city, managed by Malaysian Geospatial Data Infra-
structure (MacGDI).
2 Background and Related Works
Various compression techniques have been discussed such as geometry com-
pression by Deering (
1995
), Isenburg and Snoeyin (
2000
), Taubin et al. (
1998
) and
Touma and Gotsman (
1998
), whereas connectivity compression could be sub-
divided into edge-based compression and vertex-based compression. Rossignac
(
1999
) and Szymczak and Rossignac (
1999
) have discussed edge-based related
techniques while Alliez (
2001
) and Touma and Gotsman (
1998
) have also dis-
cussed vertex-based techniques. Not a single algorithm could serve all scenarios as
shown in the review by Peng et al. (
2005
). In Siew and Abdul Rahman (
2013
), a
schema aware compressor is invented coupling with the LZMA compression
module in the final stage. The development of the encoder is well discussed and
could be implemented as a component in web services transaction. The main idea
of the encoder is to allow ''schema-awared'' binary data transacted which could
largely reduce file size up to 8 % of original size. As compression schemes are
