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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
(http://deegree.sourceforge.net/) By using free converter,
shapefiles format data can be converted to GML data.
3.3 Application Schema Generation
Since Hong Kong base map has own specification of data
content, an application schema specified for Hong Kong base
map data is needed to validate the GML documents. Referring
to the data dictionary of Hong Kong digital base map, an
application schema declares actual feature types and property
types. It defines data types of textual data. For example, it
defines whether id should be in numeric and name should be
string. It will be further developed to include schemas for
different features such as building, road and contour etc.
3.4 XSL stylesheet Generation
In order to visualize GML data, stylesheets are required. As
mentioned in previous section, stylesheets are used to convert
and format GML into SVG and different style and symbols can
be applied. A set of recommended styles and symbols for the
portrayal of OS MasterMap data are specified. Since the Hong
Kong digital map has own style and symbols in representing
geographic features, a XSL stylesheet is need to be specially
designed.
3.5 Design algorithms for editing function
SVG offers more than vector display. SVG document can be
added, moved, modified, copied and deleted using client
triggered graphical user interface (GUI) events (Randy, 2002).
By developing some common scripting language like Javascript
the program can track the mouse and transform the user
coordinate on client machine to the user-defined coordinate
system. This makes onscreen digitizing online possible and then
allows adding and updating data. The functions will include
move, add and delete feature and vertex and modify textual
information. In order to design and implement on-line editing
capability using GML and SVG, a system will be set up. The
basic algorithms and workflow of enabling data editing is
shown in figure 4.
5
Loading m
GML data from data server |
Parsing |
GML -» SVG on the fly
oe
| Rendering
Render SVG with plug-in
T
User Interactions
erform functions by javascript
| Parsing |
SVG -» GML
Saving
post feature geometry
along with any attribute data
back to server
Figure 4 The basic workflow of data editing using GML and
SVG
161
| Editing J
raphical & textual data editin
Lo
3.6 Development and evaluation of a prototype
After all, a prototype will be developed for testing the proposed
data model and algorithms and applied for real application. The
implementation will apply Java script and SVG DOM to make
XML application and Web service. Since applications on
Window CE platform become popular and increasingly gain
market share (Legard, 2002), Window CE platform is chosen
for evaluation. There are several components in the system
including Web and data server, networking devices and mobile
devices such as tablet and pocket PC.
1 A server which is capable of storing data and retrieving
existing feature as well as carrying out update, insert, and
delete requests on spatial and non-spatial attributes.
2 Protocols like Web service for transmitting data requests
between client and server.
3 A client like internet browser or mobile devices which is
capable of displaying spatial geometries and attribute
information and allowing interactive input and editing.
In order to produce the application which can be applied in
Hong Kong, Hong Kong base map data and networking data
will be used and stored in database. The following Figure 5 is
the overview of the proposed system.
Client Browser Pen Tablets Pocket
Display
Map
= ==
Databas
Figure 5 The overview of the proposed system for the prototype
The prototype will be used to demonstrate and test the
effectiveness of the proposed data model and algorithms using
existing GIS data. The data will be stored in database and
served through Internet or wireless terminals. As both SVG and
GML are XML-based, and conversion from one to the other is
simple, GML could be used to handle GIS data and SVG to
view and deliver it to mobile users, making one the perfect
complement to the other.
Several functions including map rendering, spatial query, and
map editing will be performed. GML and SVG will be served
as vector format across the Internet. Data will be transferred as
vector on the client browser. The browsers allow users to
control their view with zoom and pan the same way they do so
in GIS software. For example, when the user wants to zoom or
pan to a different area of the map, that request is then sent back
to the GML data store, where the Web feature server will
