TRUE ORTHOIMAGE GENERATION 
IN CLOSE RANGE PHOTOGRAMMETRY 
Efstratios Stylianidis 
Dept. of Cadastre, Photogrammetry and Cartography, Aristotle University of Thessaloniki, 
stratos(@geoimaging.com.cy 
Commission V, WG V/4 
KEY WORDS: Photogrammetry, Algorithm, Orthoimage, Close Range, Digital 
ABSTRACT: 
Digital orthoimage compose an efficient and economic way for 
of information is functional when the user has to evaluate, ana 
has to be performed on a single plane and the form of the object is not rough, the process is 
rectification. 
The orthoimage production of rough objects is sti 
architectural or archaeological applications) where th 
shape of the object. In most of the cases the points with 
most established solutions used to build-up a mathematical shape description of 
e object through the rectification process. In the last few years a novel expression, 
[lustration of the object through the rectification development. 
cannot provide the ultimate representation of th 
the «true orthoimage» raised to describe the ideal i 
This paper is a contribution on the rese 
the representation of two-dimensional texture information. This kind 
lyze or measure the objects presented in the image. If the projection 
simple and well-known as simple 
Il an on-going problem especially in close-range applications (for example 
e major problem is that of the complication of the description of the analytical 
identical XY co-ordinates display different heights. Regular grids are the 
an object. In this way a conventional orthophoto 
arch for the true orthoimages. The on-going study focuses on the description and test of a 
solution which uses a 3D model for the creation of a true orthoimage in close range photogrammetric applications. 
1. INTRODUCTION 
The architectural objects consist of adequate items or structures 
that can be described mathematically. The structures are 
principally shaped by straight-line elements and usually are 
highly characterized by rapid changes in surface continuity. 
It is well known that the abrupt changes in surface represent 
boundaries in the image and natural breaklines in the object 
model. The development of tools and techniques that 
automatically or semi-automatically detect and extract such 
useful features has been discussed in various papers (Stylianidis 
et. al., 2002; Stylianidis & Patias, 2002). 
The increasing requirement for quick and accurate production 
of surface models is a fundamental sub-process in the 
framework of orthoimage generation. The development of 
orthoimages requires a known surface, what is usually 
described as DTM, DSM or DEM. 
On the other side, orthoimage is one of the most attractive 
photogrammetric product. The need for a quick production is 
always a fundamental process in geomatics. Basically, 
orthoimages can be separated. according to its production 
method, into two categories: the conventional and the true one. 
The conventional orthoimage production does not take into 
account. objects that mathematically can be described like 
buildings; due to the fact that the used DTM does not model 
such kind of objects. This has the result to distort the features 
from their correct position. 
On the other side, based on a 3D or a 2.5D model the 
orthoimage production process may take into account several 
additional information for the production of a true orthoimage. 
Various researches from different backgrounds and 
perspectives. Amhar and Ecker (Amhar & Ecker, 1996) 
proposed a novel solution for the generation of true orthoimage. 
The procedure, applied to the production of orthoimages in 
urban areas, use a DSM, which is been managed by means of a 
relational database. Bocardo et al. (Bocardo et al. 2003) 
developed software that uses terrestrial laser scanner data (very 
dense DEM) in order to produce true orthoimage. 
The paper describes the results of a research attempt for the true 
orthoimage generation. The proposed framework is of special 
interest in close-range applications. 
2. PROBLEM DEFINITION 
In close-range problems, particularly in architectural, industrial 
or archaeological applications objects that are represented on 
the images consist of mathematically structured surfaces, for 
example planes. Such cases are frequently seen in building 
facades where alcoves, balconies or any other similar structures 
appear. 
Under the above circumstances, three different approaches are 
realistic: 
= Single rectification 
= Conventional orthoimage 
= True orthoimage