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DTM Algebra applies as operands different DTMs of the 
same area carrying different epochs of the same 
information (e.g. elevation), or different types of 
information (e.g. slope or soil quality models). There 
may be used very complex expressions. This is one of 
the functions of the current SCOP.INTERSECT module 
(Sigle, 1991), parts of which should be adapted as a 
method of this class. C/assification is to incorporate the 
second important function of SCOP.INTERSECT 
allowing to classify contents of a DTM according to a 
network of polygons of any complexity (e.g., to classify 
a slope model according to cadastral boundaries). D7M 
Exploration is for compiling (deriving) different products 
o S DM. by methods such as reported in (Rieger, 
It is of mandatory importance to represent results of 
different methods not just as graphics or listings but in 
forms capable of further processing - such as, again, 
DTM structures with the derived quantities as z values. 
Slope models are a good example of this, but even 
visibility of the surface from a specified point of space 
(a by-product of the hidden line algorithm of perspective 
views) can be represented as a DTM structure. In this 
case, the elevation difference (negative, O, or positive) 
should be represented as z, to be added to the elevation 
of the DTM location so to become visible or invisible, 
respectively (Hochstoeger, 1991). 
SYSTEM INTEGRATION 
The classes as described will be integrated into two 
different versions of the DTM system: 
- a full-featured version with graphical user interface 
(GUI), command language, interactive graphics, 
etc., available for some of the most important 
platforms (such as PC workstations under OS/2 
2.* and under WINDOWS NT, some major UNIX 
workstations, and maybe DEC VMS), and 
- a major machine-independent subset of the DTM 
system, mostly for mainframes, with just the 
command language as user interface. 
Both versions will run in three modes of operation: 
- interactive mode, 
- batch mode controlled by command procedures, 
and 
- driver or slave mode, to service requests of a host 
system, without being seen by the user in any 
ways (him seeing just the user interface of the 
host system), and sending all output to that 
system. 
Integrating the DTM system into a greater application 
software environment concerning both input and output 
is of crucial importance. A new edition of the 
Topographic Information and Archiving Software 
(TOPIAS) based on TOPDB is to be integrated into the 
DTM package so to play the role of some foreign 
secretary. Messages in the syntax of standard SQL, or 
better still, of TOPSQL should enable communication in 
both directions. Servicing (TOP)SQL requests by the 
DTM system yields a good example of "lazy 
processing": requesting (SELECTing) an elevation at a 
location (x,y) will result in a message to the class DTM. 
This will check whether there is an interpolated surface 
ready at the location; if not, a message will check with 
the class of input data whether interpolation is possible, 
and so on. After some "small talk" among the classes 
exchanging messages and data, the result will be 
deduced and sent back (as INSERT statements) via 
TOPIAS to the requesting system (which could be a 
user-written program, as well). 
The driver or slave mode of operation provides fine 
means of integration with geographic information 
systems (GIS), with systems to serve analytical plotters 
(e.g. to support data acquisition: progressive sampling, 
editing, image overlay of different DTM products), or 
with interactive graphics systems. 
And furthermore, there remain such means of 
integration as DXF and other file format standards. 
Compatibility with earlier versions of SCOP must be 
ensured by supporting not only the corresponding 1/0 
formats but also both databases (DAF and RDH). 
SUMMARY 
An architecture for application software is described, as 
proposed for the new edition of the DTM package 
SCOP. It consists of fairly independent modules 
("autonomous classes’), integrated within an object- 
oriented frame. Autonomous classes can be 
implemented, in addition to object oriented 
programming, in classical procedural ways. This 
compromise has major merits at the current state of the 
software engineering practice: it provides fair portability, 
allows for integrating modules of earlier programs, from 
the user's perspective it carries clear signs of object 
orientation resulting in user friendliness, and the system 
is easily extendable by further autonomous classes. 
Some selected classes of the DTM system are 
described. Further important application classes are 
going to be created as important by-products of 
dissertations, the commercial benefits providing the 
student with means for his studies, and the application 
helping to spread new technology. 
Acknowledgment 
This study has been financed by Fonds to Promote 
Scientific Research of the Austrian government, Project 
Nr P7385-GEO. 
References 
Assmus, E., Kraus, K., 1974. Die Interpolation nach 
kleinsten Quadraten; Praediktionswerte Simulierter 
Beispiele und ihre Genauigkeiten. Deutsche 
Geodaetische Komission, Reihe A, H.76. 
Ecker, R., 1991. Rastergraphische Visualisierungen 
mittels digitaler Gelaendemodelle. Geowiss. Mitteilungen 
der Studienrichtung Vermessungswesen der TU Wien, 
Heft 38. 
Hochstoeger, F. 1989. Ein Beitrag zur Anwendung und 
Visualisierung digitaler Gelaendemodelle. Geowiss. 
Mitteilungen der Studienrichtung Vermessungswesen 
der TU Wien, Heft 34. 
Hochstoeger F., Ecker R., 1990. Application and 
Visualization Techniques for Digital Terrain Models. 
International Archives of Photogrammetry and Remote 
Sensing, Komm. IV, Vol. 28, Part 4, Tsukuba, Japan. 
Kager H., Loidolt P., 1989. Photomontagen im 
Hochbau. Vermessung, Photogrammetrie, Kulturtechnik, 
Nr.3. 
Kalmar, J., 1991. Diverse Interpolationsverfahren. 
Institut fuer Photogrammetrie und Fernerkundung, TU 
Wien. /ntern. 
Koestli, A., 1988. Manual for BC FORTRAN. BC 
Software, Bad Canstatt bei Stuttgart. 
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