ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
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instance of the Browser class. This class is the Java
encapsulation of the VRML world. It contains the entire Browser
Script Interface as well as the getNode() method, which returns a
Node when given a DEF name string (in this paper, it also act as
the ID of a object). Once a Node instance is obtained from the
getNode() method of the Browser class, it’s Eventlns an
Eventouts can be accessed. Once an instance of the desired
Eventln is obtained, an event can be sent to it. Once an instance
of a desired EventOut is obtained, the current value of the
EventOut can be gotten and a callback can be setup to be
invoked when the EventOut is generated. In this paper, EAI was
used for communicating with some viewpoint node of the VRML
world.
In the digital harbor virtual scene, each geographic object has a
viewpoint with which the geographic object displayed as highlight
of scene. All viewpoints of virtual scene form a stack, the current
viewpoint on the top of stack. When a ‘true’ message was send
to the Eventln of set_bind field of one viewpoint node, the
viewpoint would be bound and become the current viewpoint.
In the query result form, when a data record was selected, a
Java applet at the same page with VRML world would obtain the
correlative viewpoint node according to the DEF name string.
Then getEventln() method of the viewpoint node class returns
the “set_bind” Eventln by passed a string of "set_bind”, and
setValue() method send ‘true’ event to the “set_bind” Eventln,
make the viewpoint become the current viewpoint, and the
geographic object with this viewpoint would be displayed as
highlight (Show in Fig4).
4. CONCLUSION
In this paper, VRML technology was tried to create a dynamic
and multi-dimensional digital harbor system. It can be concluded
that integrated with thinking of GIS and EAI VRML was powerful
enough to create great multi-dimensional geographic information
system on Internet. But further study should be done on
three-dimensional spatial analysis in VRML world.
Multi-users is also a good developing direction. When multiple
users access a VRML world at same time, replacement of them
appear in the VRML scene which can be seen by each other.
Multi-user thinking can be applied in the digital harbor system by
such way: ship that will access the port appears in the digital
harbor at the right position as reality which imported from GPS,
so the ship’s watcher can observe the position and action of
other ships direct from the digital harbor system.
Fig4. Using Java applet control viewpoint of VRML world
5. Reference:
Ames A L, Nadeau D R, Moreland J L, 1998, VRML Resource
Book, Beijing, Publishing House of Electronic Industry.
Lli Hongga, Cui Weihong, 1999, Virtual Reality in “Digital Earth”,
Beijing, China Environmental Science Press.
Li Qi, Yang Chaowei, Wang Jinao, 1999, The Design and
implementation of WebGIS, Beijing, China Environmental
Science Press.
Rrodger Lea, Kouichi Matsuda, Ken Miyashita, 1999, Java for 3D
and VRML world, Beijing, Publishing House of Electronic
Industry.
