GRID 
1sisten- 
also as 
fferen- 
ind the 
ns exist 
gorous 
2). But 
ovided 
nt data 
rain 
d data 
né 
DTM. 
| easier 
al data 
;there 
1e TIN 
nation 
e data 
n con- 
occur, 
:S part 
3RID. 
f non- 
, spot, 
makes 
height 
information. However it has all the disadvantages of the 
GRID in terms of data consistency and DTM genera- 
tion. 
5. CONCLUSIONS AND OUTLOOK 
Integration of DTM into GIS is a difficult task which 
should be solved in near future. In this way the query 
space of the GIS can be extended considerably. DTM 
management and DTM generation within a GIS should 
objectwise be carried out. Separated data sets in situa- 
tion and terrain make sense if the DTM is introduced as 
reference surface of the GIS. This separation allows for 
fast GIS response when queries relate to only one of both 
data sets. However, these conclusions are only valid for 
boundary representations. 
As far as other geometric modelling techniques are used, 
it becomes more difficult. In this case, a lot of research 
should be done on three-dimensional data structures 
including three-dimensional topology. The experience 
we get during the introduction of a DTM as reference 
surface in a GIS can be the basis for more advanced 
three-dimensional data models. 
6. REFERENCES 
Bill,R.,Fritsch,D.,1991: Grundlagen der Geo-Informa- 
tionssysteme, Band 1. Wichmann, Karlsruhe, 437 p. 
Bill R.,Fritsch,D.,1992: Grundlagen der Geo-Informa- 
tionssysteme, Band 2. Wichmann, Karlsruhe, 440 p. 
Düsedau,G.,HóDler,R., Reinhardt, W.,Thiemann,R.,19 
87: Digitale Gelándemodelle - Neue Entwicklungen 
und Móglichkeiten. Bildmessung und Luftbildwesen 
55, pp. 175-194. 
Ebner,H.,ReiB,P.,1978: Height Interpolation bythe Me- 
thod of Finite Elements. Nachrichten aus dem Kar- 
ten- und Vermessungswesen, Reihe II, Heft 36, 
pp.79-94. 
Ebner,H.,Fritsch,D.,1986: High Fidelity Digital Eleva- 
tion Models - Elements of Land Information Sys- 
tems. Proceed. 18. Int. Congr. Survey. (FIG), Comm. 
V, Toronto, pp. 155-170. 
503 
Ebner,H.,Hossler,R.,Wiirlinder,R.,1990: Integration of 
an Efficient DTM Program Package into Geographi- 
cal Information Systems. Int. ArchPhRS, Vol. 28, 
Part 4, pp. 116-121. 
Ebner,H.,Eder,K.,1992: State-of-the-art in Digital Ter- 
rain Modelling. Proceed. EGIS'92, Munich, pp. 681- 
690. 
Fritsch,D.,1990a: Towards three-dimensional data 
structures in geographic information systems. Proce- 
ed. EGIS'90, Amsterdam, pp. 335-345. 
Fritsch,D.,1990b: Integration of digital terrain models in 
GIS. Lecture notes, SIGIS Workshop no. 5, Paris. 
Fritsch,D.,1991: Raumbezogene Informationssysteme 
und digitale Geländemodelle. Deutsche Geod. Kom- 
mission, Reihe C, Nr. 369, München. 
Fritsch,D.,Pfannenstein,A.,1992: Conceptual Models 
for Efficient DTM Integration into GIS. Proceed. 
EGIS'92, Munich, pp. 701-710. 
Hôhle,J.,1991: Digital orthophotos and object-oriented 
height models in GIS. Pres. Pap. AM/FM Conf, 
Mariehamn. 
Koch,K.R.,1973: Hôheninterpolation mittels gleitender 
Schrágebene und Prádiktion. Vermessung, Photo- 
grammetrie, Kulturtechnik, 71, pp. 229-232. 
Kraus,K.,1972: Interpolation nach kleinsten Quadraten. 
Bildmessung und Luftbildwesen 40, pp. 3-8. 
Reinhardt, W.,1991: Zur Integration von Digitalen Ge- 
lándemodellen in GIS. In: Geo-Informatik, Ed. M. 
Schilcher, Siemens Nixdorf Informationssysteme 
AG, München, pp. 107-118. 
ReiD,P.,1985: Aufbau digitaler Hóhenmodelle auf der 
Grundlage einfacher finiter Elemente. Deutsche 
Geod. Kommission, Reihe C, Nr. 315.