SAR 
d in 
after 
SAR 
reas 
lity. 
for 
le, a 
nent 
997, 
à 1/1 
| GLI 
and 
ving 
ads, 
eln, 
ireat 
17th 
VISUAL INTERACTION WITH VERY LARGE SPATIAL DATA SETS 
Wolfgang Walcher 
Institute for Computer Graphics, Technical University Graz, Austria 
E-mail: walcher@icg.tu-graz.ac.at 
ISPRS - Commission I, Working Group 6 
KEY WORDS: Satellite, Image, Database, Visualization, Software 
ABSTRACT 
The number of remote sensing instruments as well as the size and quality of the generated data is increasing continuously. Electronic 
catalogues produced by the different data providers are very important tools for search and retrieval of remote sensing images. The 
World Wide Web within the last years became the most important means of providing this kind of information to the world-wide 
user community. The HTTP protocol and general problems with the bandwidth on the Internet limits some functionality in these 
information systems. New Java™ based network software overcomes these restrictions and makes it possible to implement a new 
generation of tools for the interaction with image and data catalogues. This paper describes typical problems with today’s stand- 
alone or WW W-based image and metadata information systems. It also describes what kind of data visualization is needed to ease 
the user’s interaction with these systems and how these visualizations can be implemented using the Java programming language. To 
illustrate the proposed concepts a new kind of data catalogue interface for SAR radar image data was implemented to support the 
analysis of data from the Magellan mission to Venus. The paper also offers an outlook on how this new kind of network software 
can be used to integrate so far unknown functionality into upcoming WW W-based information systems for remote sensing data. 
1 INTRODUCTION potential customers of these data. Typically this software is 
executable on a single or very few hard- and software 
1.1 Background environments. But since it was written using a high level 
programming language any desired functionality can be 
Within the past years an increasing number of sensors along implemented. Disadvantages of this concept are the limited 
with an also increasing geometric and radiometric resolution of variety of supported hardware and software environments and 
the resulting images are producing an almost exploding amount the need for separate software tools with different capabilities 
of remotely sensed digital data. Ambitious programs like and user interface to access every single image data archive. 
NASA’s ‘Mission to Planet Earth’ are boosting this : 
development even further. While in general users should benefit ~~ Providers of remote sensing data therefore are increasingly 
from such better datasets at greater accuracy, it becomes more using World Wide Web based catalogue systems. The two main 
difficult for that user to find the very data best suited for a reasons for this development are that today’s WWW browser 
given problem or application. software is inexpensive or even free of charge, and browsers are 
available for almost any hardware and software environment. 
Electronic catalogues and information systems are being set up The ease of use of a hypertext browser and the general boom of 
by the private or public organizations which provide remote the WWW are also reasons for this trend. 
sensing data. But also the number of these catalogues is 
increasing in a way that it has become necessary to introduce Offering a WWW-based retrieval client can increase the 
catalogues of catalogues like the International Directory ^ number of accesses to a catalogue system almost exponentially. 
Network (IDN, see CEOS, 1994) or the European Wide Service With the introduction of the WWW interface for the IDN at 
Exchange (EWSE, 1995). In general catalogues closer to the NASA's Global Change Master Directory (GCMD), the 
date producer contain more detailed information, even images. average number of requests per day was increasing from about 
Systems like IDN offer mostly metadata and descriptive 200 in August 1994 to almost 4000 in February 1996. 
information about entire datasets. 
1.3 Standard functionality of catalogue systems 
Only completed missions, like those to other planets have a 
fixed-size data set. Otherwise perpetual growth of remote There are four basic components from which catalogue systems 
sensing image archives, requires that all catalogues be updated are usually built. Only components 1 and 4 are necessary to 
continuously. To make these rapid changes visible to the user, create a fully operational system, whereas all of components 2 
on-line access is a must. Therefore the Internet is becoming the and 3 or only parts are sometimes missing. 
most important medium to present remote sensing data to the ; 
world-wide user community. 1 Query definition and retrieval of results is the basic 
function of all catalogue systems. This part of the system is 
responsible for the generation of queries to the underlying 
database. In WWW-based systems HTML forms are used for 
Special purpose software tools exit to communicate with a the definition of the query at the users site and CGI - scripts to 
given remote sensing archive and are being distributed to ~~ implement the interface to a relational database. 
1.2 Image catalogues 
197 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996