JIS
ces
ork
the
ess
the
ect
ap
to
ich
ser
sad
ers
es,
ing
the
ear
ext
ces
ns-
ra
jon
ces
jer-
'nel
asic
HTML utility services. User level services combine one or
more system level services into higher level services, directly
accessable to users. À possible generalization and extension
of this model has been decribed in (Koschel et al., 1996).
3.1 Services based approach
The services based approach offers the possibility to imple-
ment well defined services (interfaces, methods, data) in dif-
ferent ways.For example the access to the MEROS database
has been implemented by using a batch oriented access TZUI
(Bussmann et al., 1995) while UDK (Kramer and Spandl,
1995) and GRDB accesses have been realized by ORACLE
ESQL programs.
3.2 Outlook
Currently system services are more or less located on fixed
servers. The systems are based on different technology as
outlined in section 3.1. To make these services access-
able in a distributed manner a middleware layer based on
CORBA should be introduced (Object-Management-Group,
1995). This will ideally make the system services part of the
ElS-architecture independent of location, low level access and
administration technology. Our future work will concentrate
on these aspects of an EIS.
4 VISUALIZATION FACILITIES
Visualization of datasets is an essential task in information
systems. In an EIS it is necessary to handle tabular and spatial
data. Tabular data are georeferenced also.
From a user's point of view a visualization facility should of-
fer the possibility to select several layers from existing map
themes and add non graphical data (e.g. pollution measure-
ments) to create a thematic map.
4.1 Requirements
In UIS-BW all geographical data are stored in the RIPS (Spa-
tial Information and Planning System). RIPS has been im ple-
mented as a SmallWorld GIS application, archiving raster and
vector data of scales 1:5000 to 1:1000000. Access to these
data was mandatory.
Non spatial (tabular) data is being stored in several different
database systems based on ORACLE and ADABAS running
on VAX/VMS and Unix systems. Data from these systems
had to be visualized as line and bar charts.
It should be possible to patch together maps and charts into
one thematic map.
Final maps, other graphics and tabular data should be export-
able to the file store of a client workstation. Further massaging
and integration into reports using existing office automation
software was a must.
4.2 Implementation
The current WWW facilities for graphically oriented interac-
tions are quite limited. Imagemaps allow a single click only.
It is not possible to select areas of interest or even bounding
boxes.
GIF raster images have been the only graphical data type
available for display by then current WWW browsers.
At the start of the project an online programmatic interface
to the SmallWorld datastore did not exist, so we had to find
a different solution for accessing the spatial data.
403
The basic idea - guided by the current WWW functionality -
is, to paint maps on the server into a raster file. A user has to
select areas of interest, map themes, tabular data and define
mapping attributes. The task is then carried out by server
side CGI applications.
In order to generate maps and to provide complex GIS func-
tionality we use the public domain tool GRASS, which is a
raster oriented GIS that supports digital image processing,
map generation and several vector operations. GRASS is im-
plemented in C and is available on UNIX platforms (USA-
CERL, 1995a). The use of a public domain GIS enables error-
debugging at any time and the extension of the existing pool
of methods, since the source code is available. There is also
a lot of documentation, including a beginner's, a reference
and a programmer's manual, where most of the GRASS lib-
rary functions and formats are documented. In addition the
GRASS mailing list (USA-CERL, 1995b) is helpful in solving
problems.
Another problem to solve was the connectionlessness of the
HTTP. GRASS uses a mapset concept, where maps and res-
ults belong to a certain user. As an unknown number of UIS-
users will access the system simultaneously, we had to im ple-
ment a user session concept. This allows to create temporary
and persistent results by introducing a workspace model.
We decided not to use hidden variables to transfer the ses-
sion context but to create a server side database storing all
HTML page contexts. We are using TCL (Tool Command
Language) (Ousterhout, 1994) to write all CGI scripts and
administration programs. TCL has proved to be very rich
in functionality for this task, but not being as demanding on
computer resources as PERL is. Details of the implementation
have been published in (Wiesel and Hagg, 1995). A library of
TCL functions (Hofmann, 1996) has been developed to facil-
itate writing of interactive HTML application pages without
specific knowledge of HTML. This toolkit is based on a call-
back mechanism similar to the X Windows system. It could
be adapted to other page description languages quite easily.
4.3 Map Display Functions
Figure 2 shows the overall architecture of the mapping ser-
vice. GIS data are imported from an external GIS (RIPS in
our case) into GRASS. Geodata and metadata are stored in-
side the GRASS mapset system. Users communicate with
the GIS services by selecting themes (GIS-Metadata service).
Currently raster and vector data can be combined by select-
ing map names and theme names. Geographical regions have
to be specified by the name of an administration unit (e.g.
a county name) or by entering coordinates, map names or
bounding boxes. After selection of input data, the map con-
tents are painted on the WWW server by a heavily modified
version of ps .map, which creates a PPM (Anonymous, 1995)
raster file. Colours and other map layout attributes can be
specified, but default values are supplied as well.
4.4 Business Graphics
To draw line, bar and pie charts we are using GNUPLOT (An-
onymous, 1994). GNUPLOT offers a rich set of functionality
for plotting of scientific data and mathematical functions (1D,
2D, 3D), but unfortunately it is not very efficient in drawing
business graphics. We had to write a fairly big amount of pro-
grams in the GNUPLOT macro language to adapt it to our
needs. We are still looking into something better suited to
the task of visualizing tabular data similar to the MS-EXCEL
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
M "
