102 
the new VRML standard language to represent a 3D geometry. VRML supports the representation 
and rendering of a polyhedral geometry, by storing not only geometrical information but also 
colour parameters and even textures. The rendering is based on accurate shading techniques, and it 
is a task entirely demanded to the programmer to determine the colour attribute of each triangle of 
the polyhedral geometry. This characteristics makes VRML a useful standard that is perfectly 
suited to our purpose: colour attributes are derived from an accurate analysis of spectral 
reflectancies of a given terrain, as described in a former paragraph. VRML supports exploratory 
navigation in quasi-real time taking advantage of the computational power of the available 
workstation. A special module of TISS allows us to code into VRML language any DEM, 
considering also its colour attributes or texture. To make navigation easy and visually effective. 
VRML supports different level of details of the rendering process: therefore we can create 
hierarchical models of a Landscape, with increasing geometric accuracy, and depending on the 
viewpoint distance the desired level of details is presented to the end user. 
Once a VRML based DEM is available, another important feature that opens up the 
possibility of implementing queries and "what if" simulation, is the compatibility of VRML 
language with the standard mark-up HTML protocol. This protocol allows us to distribute across a 
wide area network (WAN) the relevant information, and to implement a kind of distributed GIS. It 
is a very easy task to associate a universal resource locator reference (URL. which identifies a 
remote computer storing the desired information) to a given DEM element, so that another VRML 
model or sub model can be retrieved, as well as to access a remote data base or an information 
page, which respect the standard of the current World Wide WEB technology. 
Moreover, being a geometric modelling language. VRML allows us to represent not only a 
DEM but also a geometric model of some anthropic object. In the figure 4 an example is presented 
of the geometric reconstruction of the old Roman Theatre of the town of Aosta, in its environment 
represented as a DEM model. 
The example shows the effect of texturing a photograph of the archaeological site on the 
ground, while in figure 5 it is exemplified the access to a data-base page, containing information 
on the characteristics of the building; in this example a context sensitive area on the geometric 
model of the theatre has been defined, which links to the desired page of the database archive. 
The new standard language JAVA (December, 1996). is another useful tool to implement a 
better access to a data base and to create interactive applications that can be run on a WAN 
environment. JAVA is a hardware independent, object oriented language, that provides, among 
the typical characteristics of any programming language, constructs to access remotely located host 
computer systems, and to run both locally and remotely an application program, like a database 
query. Future development of the present project will implement JAVA based applications to 
improve the level of interactivity with a DEM. that will become, therefore, an effective visual 
access tool to GIS information 
5.0 CONCLUSION 
Virtual reality methods are now powerful techniques to support landscape and territorial 
study. TISS is an integrated system that support 3-D reconstruction of a DEM and its analysis 
from Earth scientist's viewpoint.