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1.3 Implementation 
The ASRO module is built in four levels. 
The first level uses an existing C++ visualisation library: VTK (Visualization Toolkit). It is an “open source, freely available software 
system for 3D computer graphics, image processing, and visualization”. It provides basic methods to define, show and transform 3D 
data. 
The second level implements the general structure of the module in a set of new C++ classes. An efficient low-level language allows 
computation intensive functions to perform fast. 
The third level implements a set of commands giving access to the C++ classes of the second level. They are extensions of the Tel 
scripting language (Tool Command Language). Scripting languages gives more flexibility to the user who can customize the code 
(not compiled). It also helps the developer who can test his program more easily. New Tel commands can be written in C++. They 
are compiled in a library (DLL) that can be loaded in a Tel interpreter, extending the functionalities. The code can be written 
manually but we used a freely available software tool, SWIG to automate the process. SWIG connects programs written in a variety 
of low-level programming language (such as C++) with a variety of high-level languages (such as Tcl/Tk). It automatically creates 
interface code using the original C++ classes’ headers and files specifying the interface. 
The fourth level uses the original Tel commands; the one developed in the third level and Tk commands to build a user interface. Tk 
(toolkit) comes with Tel (usually referred as Tcl/Tk), it allows to quickly create graphical applications. 
The user can interact with the model at the third level (with commands typed in a console window) or at the fourth (with the 
graphical user interfaces). All the actions are recorded in a log file. This allows the user to reconstruct a previous stage of the model 
(not yet automatically). Log files are also a record of how something was done and by whom and open the possibility to judge about 
the quality of every piece of information of the model. 
The ability to store set of commands in small files, Tel scripts, allows storing the key used to produce a result instead of the results 
itself. This can save memory and remain valid if the model is changed. 
Dealing with monuments, long-term concern is an issue. Text files are used for the databases. They always start with an explanation 
of the format. In this way, the chance to recover information in the future is maximized. 
2. MODEL CONSTRUCTION 
Fig. 2: Model of a Garden pavilion of Park Abbey in Leuven 
In the following two sections, the functionalities of the software will be presented. 
The product of ESAT and PMA modules is a file describing a textured triangle mesh (figure 2). The file contains also information 
about the data origin. This forms the ‘objective’ part of the model.