AN INTEGRATED SOLUTION FOR THE PROBLEMS OF 3D MAN-MADE OBJECTS 
IN DIGITAL ORTHOPHOTOS 
Fahmi Amhar "^, Robert Ecker * 
"The National Coordination Agency for Surveys and Mapping (Bakosurtanal) 
JI. Raya Jakarta-Bogor Km. 46 Cibinong, Indonesia 
Fax: (462-21)-8753067 
? Institute for Photogrammetry and Remote Sensing, Vienna University of Technology 
GuBhausstr. 27-29 A-1040 Vienna, Austria 
E-mail: famhar@fbgeo1.tuwien.ac.at 
Fax: (+43-1)-5056268 
ISPRS Comission IV, WG 4 - DEM and Digital Orthoimages for Mapping / GIS Applications 
KEY WORDS: Digital Orthophoto, Orthoimage, DEM/DTM, Digital Building Model, CAD 
ABSTRACT: 
Especially for geographic information systems (GIS) of urban areas large scale digital orthophotos are increasingly 
important. Inadequate description of 3D man-made objects and conventional orthophoto algorithms cause geometric 
errors visible in form of displacement and double mapping. A solution for precise mapping based on image separation 
and independent rectification of terrain and building areas will be presented. An integrated solution should handle all 
related tasks that are object acquisition, modelling and orthophoto generation. 
KURZFASSUNG: 
In städtischen Gebieten sind großmaßstäbliche digitale Orthophotos für geographische Informationssysteme von 
großer Bedeutung. Aufgrund des üblicherweise angewandten Algorithmus zur Orthophotoherstellung, sowie der 
unzureichenden Modellierung von Kunstbauten ergeben sich Fehler in Form von geometrischen Versetzungen und 
Doppelabbildungen. In diesem Bericht wird eine Methode zur Herstellung von geometrisch exakten Orthophotos 
vorgestellt. Sie basiert auf einer unabhängigen Entzerrung von Kunstbauten und Gelände mittels vorangegangener 
Bildseparation. Anschließend werden Vorschläge für ein umfassendes System zur Herstellung digitaler Orthophotos 
diskutiert. 
1. INTRODUCTION on image separation and independent rectification of 
terrain and building areas. 
Digital orthophotos in combination with GIS are a usefull 
instrument for monitoring changes in rapidly growing 1.1 Mapping Problems 
cities. It is expected that in the 21* century, more than 
70% of earth citizens will live in cities. Therefore Today's orthophoto systems use only Digital Terrain 
accurate mapping of cities in digital orthophotos is very Models (DTM), but do not care about buildings. 
important. Displacement and double mapping as can be seen from 
figure-1 are the results of inadequate description of the 
Today's systems for digital orthophoto generation do not shape of 3D man-made objects and the algorithms 
model 3D man-made objects such as buildings, bridges applied. 
or multilevel highways (in this paper, „building“ and „3D 
man-made object" will be used as synonym). Therefore Figure 1a shows the terrain surface modelled by the DTM 
large scale (i.e. 1:5000 - 1:10000) orthophotos of urban and a bridge. Since the shape of the bridge is not 
areas show disturbing geometric errors in form of modelled at all, the bridge will be displaced as can be 
displacement and double mapping. seen in layer ,conventional orthophoto*. The proper 
position is marked in layer ,correct orthophoto“. In Figure 
Erroneous pixels in common digital orthophotos amount — 1b the building is included in the DTM. This approach 
to about 8% and more - depending mainly on building results in a correct position of the roof pixels in the 
density and height (Amhar, Ecker, 1995). This causes orthophoto, but has the disadvantage of double mapping 
serious problems for further applications such as data in hidden surface areas. 
overlay, 2D coordinate measurement or 3D visualization. 
This paper presents a method for accurate mapping of 
3D man-made objects in digital orthophotos. It is based 
84 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
  
  
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