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A LOW-COAST MMS INTEGRATING GPS, DIGITAL COMPASS AND A CAMERA TO 
THE DIRECT GEOREFERENCING OF DIGITAL IMAGES 
Margherita Fiani” , Pasquale Pistillo* 
* Dipartimento di Ingegneria Civile, Università di Salerno, Via Ponte Don Melillo, 1 - 84084 Fisciano (Salerno), Italy 
(m.fiani, ppistillo)@unisa.it 
KEY WORDS: Mobile Mapping System, Digital Photogrammetry, GPS, Digital Compass. 
ABSTRACT : 
A low-cost, easily transportable Mobile Mapping System (MMS) was designed and built to obtain the direct georeferencing parameters 
of images; its components are a GPS receiver, a digital compass and a digital camera. 
The main aim of the system is to directly define the orientation parameters of an image. The accuracy of the 3D coordinates of the 
points belonging to the object photographed is a consequence of the whole process which involves GPS positioning, compass angle 
determination, system calibration and any other useful auxiliary data that can be used to improve the accuracy of the system (GCPs 
coordinates, distance between the object and the camera, etc.). The tests carried out up until now have demonstrated the “theoretical” 
huge potential of the measuring system as well as its versatility. This system could in fact be used to carry out surveys using vehicles 
such as cars, helicopters and boats. 
1. INTRODUCTION 
The validity of photogrammetry in surveying areas that are either 
difficult to reach or to operate in is evident, considering that it is 
possible to describe the territory without actually having to go 
over it. There is, as well, a high degree of accuracy, depending on 
the scale of the frames. The degree of accuracy also depends on 
the aim of the survey as well as the scale of the map produced. 
Nevertheless, there are cases when classic photogrammetry does 
not give satisfying results. This is the case with the Amalfitana 
Coast in Italy, a hydrological risk area, considered to be of high 
environmental value and protected by UNESCO. The verticality 
of the rugged coasts, with the added feature of all the coast walls 
facing the sea as well as the particular lay out of the road that 
runs along it, make it almost impossible to follow the standard 
procedure of placing a camera on solid ground and positioning 
the Ground Control Points (GCPs) on the cliff. 
In order to overcome this problem, we have decided to use a 
motorboat with a digital camera and GPS aboard, thus making it 
easier to reach any isolated areas and photograph them from the 
most suitable position. The movement of the boat (roll and pitch) 
made it difficult to set the exterior orientation of the camera, 
necessary in order to know with precision the changing position 
of the centre of the camera lens. A low-cost, easily transportable 
system was built and tested, to reduce the problems created by 
the difficult conditions under which the survey was carried out. 
The system was made up of the following: 
- Digital camera; 
- GPS receiver; 
- Digital compass; 
- Portable Computer. 
The aim of this study is to verify the efficiency and the 
correspondence to pre-set precision requisites of non-standard 
techniques used in surveying difficult-to-reach vertical surfaces. 
The possibility of carrying out a survey from a boat, with 
corresponding operative efficiency and reliability requisites will 
also be studied. The system was field-tested on the tower at 
Cetara (SA) and will subsequently undergo testing along the 
Amalfitana Coast, from a motorboat, in order to assess both 
precision and actual productivity. 
2. DESCRIPTION OF THE MEASURING SYSTEM 
A prototype measuring system called POLIFEMO (see figure 1) 
was designed and built to obtain the direct georeferencing 
parameters of selected images. 
  
Figure 1. Diagram of the Mobile Mapping System 
"POLIFEMO" 
The system was made up of an aluminium bar measuring approx. 
30 x 10 x lem with perfectly flat and parallel sides. A digital 
camera was fixed in the centre and a GPS antenna onto one of 
the ends. A compass was mounted onto a 30 cm aluminium 
support that was then attached to the bar in order to increase the 
distance from the camera, with the aim of accurately measuring 
the angles. All the measurements, absolute and relative between 
the various elements of the system were calibrated to the order of 
the millimetre. The bar was then screwed onto an adaptor that 
allowed it to be positioned using a standard topographic base. 
The hardware components of the system are described in the 
following section.