Istanbul 2004 
Models from 
/, Netherlands 
ww.toposys. 
gis databases 
International 
, Vol. XXXIII 
vision of gis 
| of the Eight 
ormation Sys- 
natic building 
odels. ISPRS 
D), pp. 38-49. 
GPS/INS SYSTEMS FOR COMPILATION 
OF DIGITAL LARGE-SCALE ORTHOPHOTOS 
G. Dardanelli, D. Emmolo, V. Franco, M. Lo Brutto, P. Orlando, B. Villa 
Dipartimento di Rappresentazione, Università di Palermo, viale delle Scienze, 90128 Palermo, Italy 
vifranco@unipa.it, lobrutto@unipa.it, bevilla@unipa.it 
Commission IV, WG IC II/4 
KEY WORDS: Photogrammetry, Mapping, Orthoimage, GPS/INS, Orientation 
ABSTRACT: 
The paper describes the first results of a study, supported by an Italian research project “Integrated Inertial Positioning Systems in 
Aerial Photogrammetry” on the potential use of these techniques for production of digital large scale orthophotos. The study has 
been done with aerial photographs collected from two different flights executed in Sicily: the former, relating to the city of Palermo, 
at average scale of 1:9300; the latter, over the city of Catania, at average scale of 1:2000. For both flights the orthorectification was 
carried out by direct georeferencing methods and by traditional photogrammetric techniques, using ground control points surveyed 
by means GPS techniques and aerial digital triangulation. The orthophotos generated by both methods were compared between 
themselves checking the influence of integrated sensors on the accuracy of the final product. 
1. INTRODUCTION 
The problem of the direct georeferencing is nowadays one of 
the most interesting and current topics in the aerial 
photogrammetry sector. In fact, the possibility to obtain directly 
the exterior orientation parameters of all photographs (angular 
attitude and perspective centers coordinates) without recurring 
to ground control points seems particularly advantageous 
especially in the sphere of the aerial photography for mapping 
purposes, giving new expectations that were unimaginable until 
a few years ago. 
The results regarding the accuracy of direct exterior orientation 
for photogrammetric flights at scale of 1:5000 have highlighted 
values compatible with accuracy required for the orthophoto 
production (Heipke et al., 2002); the introduction of a certain 
number of tie points and some GCPs improves the accuracy of 
orientation remarkably and reduces the existing parallax errors. 
This approach, called integrated orientation systems, seems to 
be the one that permits to obtain the highest accuracy (Cramer, 
2003). 
This research, conducted within the national interest research 
program (COFIN2002) "Integrated positioning systems in aerial 
photogrammetry” coordinated by Prof. Galetto (Galetto & 
Casella, 2003), shows the first results of an experimentation on 
the capability of the GPS/INS integrated systems, realized on 
two different photogrammetric blocks. The flights were 
executed by CGR from Parma (Italy) and aimed towards the 
commercial production of inner cities digital orthophotos at 
large (1:2000) and very large (1:500 and 1:200) scale. 
2. DESCRIPTION OF DATA SETS 
Aerial photographs used for the experimentation are relative to 
two flights done on the 6" October 2001 and 10" October 2003 
on the cities of Palermo and Catania (fig. 1), within the project 
regarding the realization of the main Italian cities digital 
orthophotos at large scale. Photographs were taken by a Leica 
RC30 camera, with a focal length of about 300 mm and 
575 
  
provided with POS/AV 510 Applanix system. The flight over 
inner city of Palermo consists of three strips with E-W 
direction, each one having 7 photographs at average scale of 
1:9300 (fig. 2); regarding to the flight over old city centre of 
Catania, a block was taken in consideration consisting of three 
strips with E-W direction, with 19 photographs in all at average 
scale of 1:2000 (fig. 3). All the photographs were scanned by 
Zeiss SCAI scanner with a resolution of 14 um, corresponding 
to about 13 cm .at scale of 1:9300 and 3 cm at scale of 1:2000. 
CGR provided the exterior orientation parameters of each 
photograph, obtained directly from the Applanix system. 
Before photogrammetric operations some ground control points 
(GCPs) and check points (CPs), chosen in correspondence of 
natural, well-defined, objects and well-distributed on the 
photographs, were surveyed by GPS method. 47 and 12 points, 
for the blocks of Palermo and Catania respectively, were 
surveyed in all, using three Topcon Legacy-H dual frequency 
GPS receivers. RMS coordinates is in the order of one 
centimeter. 
Palermo 
  
Catania 
  
Figure |. Test’s areas