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Now, if a look at existing software is taken, one 
will probably find out that most components (data 
bases; functional, statistical and numerical modules) 
are more or less alike. However, the discrete parts 
are either very different or, even worse, they are not 
clearly separated from the rest of the software. This 
is an indication that, still today, the discrete model 
and the corresponding discrete software modules are 
missing concepts in our systems. 
As a discrete network model the concept of hyper- 
graph is proposed [2][p. 389] (see as well [5, 6]). If 
V is a a finite non empty set and E, E C P(V), a 
family of non empty subsets of V such that 
U E -v, 
E;cE 
then the couple H, H — (V, E), is called a hypergraph. 
The elements of V are referred to as the vertices of the 
hypergraph. The edges or hyperedges are the elements 
of E. 
The vertices of the hypergraph clearly correspond 
to the network parameters and the hyperedges to 
the observations. Note the n-to-1 correspondence be- 
tween observations and hyperedges and, accordingly, 
the same correspondence between the design block 
[sparse] matrix of the adjustment. An additional ad- 
vantage [5], is that if H is a network discrete model 
—i.e., a hypergraph— then the representative graph 
G of the dual hypergraph H* is the graph of the net- 
work in the usual sense: an edge between two vertices 
(parameters) exists if the two parameters are involved 
in a same observation. 
In short, all the structural information of the net- 
work is contained in its associated hypergraph. (For 
other additional properties see [5, 6].) 
5 SYSTEM DESIGN 
The coding of the first modules of GeoTeX/ACX 
started by the end of 1988. Their architecture is a 
compromise between the ideas described here, in [4, 
5, 6], and the means available.” 
5.1 GeoTeX architecture 
From the architectural standpoint, GeoTeX is a sys- 
tem consisting of two types of software components: 
heavyweight and desktop applications. This classi- 
fication is based on two criteria: the complexity of 
  
5To be honest, the maturing of some of these ideas were not 
completely independent of the simultaneous realization of the 
software. 
661 
  
  
Type Complexity Environment Examples 
Main High Full ACX, GAI 
Utility Medium Full Plotting 
Desktop Low None Coordinate transf. 
  
Table 1: GeoTeX software components. 
the functions to be implemented by the software — 
and therefore, its size— and the working environ- 
ment required. Within the context of the GeoTeX 
system, a working environment is a standardized set 
of input/output files, user procedures and system re- 
sources. See Section 4.1 for a description of the Geo- 
TeX I/O kernel and Section 5.2 for more information 
about procedures. 
Heavyweight applications are the most complex 
and a full working environment is required. On the 
contrary, an almost non-existent environment is used 
to run the much simpler desktop applications (usu- 
ally, screen interaction). 
From a photogrammetric/geodetic point of view, 
the heavyweight applications are divided into main 
and utility applications. This classification is made 
for the sake of practical use. Main applications 
are much more demanding in terms of computer re- 
sources (usually main applications are executed in 
batch mode and utility applications in interactive 
mode). 
The software components of the GeoTeX system 
are listed in Table 1. 
The GeoTeX files may be classified into two groups: 
user and system files. The user files are those cre- 
ated and modified by the user during the life of each 
project (that is, the usual input/output files required 
by any system). 
The system files are the implementation —using 
the available resources and tools— of the abstract 
data types used to model geodetic data. These files 
remain unchanged during the exploitation of the sys- 
tem but may be modified by the advanced users to 
upgrade or expand GeoTeX (correspond to the Geo- 
TeX input files in Figure 3). 
In a near future (see Section 6 and Fig- 
ure 3), GeoTeX will be able to interface with 
geodetic/photogrammetric, topographic and other 
databases by means of utility applications. 
A workstation (with the set of graphic/alpha- 
numeric functionalities required to run the selected 
interface level) and a DIN A3 fast PostScript plotter 
—for work plots— is the minimum local configura- 
tion recommended to run GeoTeX. Additionally, a 
link to the LAN of the organization would be advis- 
able —mainly when photogrammetric/geodetic etc.