ADVANCES IN GPS-ASSISTED HELICOPTER PHOTOGRAMMETRY 
    
AND ITS APPLICATION TO HIGH PRECISION HIGHWAY PROFILING 
Martin J Smith and Chris | H Joy 
Institute of Engineering Surveying and Space Geodesy 
The University of Nottingham 
University Park 
Nottingham 
United Kingdom 
ISPRS Commission Ill, Working Group III/1 
KEY WORDS: Aerial, Photogrammetry, Mapping, Engineering, GPS, Bundle Adjustment, Systems. 
ABSTRACT 
An efficient road network is essential for a country's economic activity. Therefore, it is necessary to minimise any effects 
of maintenance and expansion programmes. Around ten years ago, Photarc Surveys Limited of Harrogate UK decided 
to address the problem of using traditional terrestrial survey techniques to provide essential highway profiles. A non- 
contact photogrammetric system was conceived and developed to provide the necessary data without disturbing traffic 
flow. A Zeiss UMK 10/1318 Universal Camera is 'cradled' out of the rear door of a Bell 206B Jet Ranger helicopter to 
capture images of the highway from a typical altitude of 75m. Single model analytical analysis is then utilised to give 
regular grids of road spot heights to RMSE +0.005m using control points surveyed at 40m intervals along the hard 
shoulder of the highway (Smith and Joy, 19953). 
Despite the ability of the system to provide clients with cost effective profiles, the requirement for full ground control 
along the hard shoulder is undesirable both for financial and safety reasons. The Institute of Engineering Surveying and 
Space Geodesy became involved in late 1993 with two distinctive aims. These were, firstly, that aerial triangulation 
should be applied in the analytical analysis to quantify the potential for reducing ground control. Secondly, that the 
Institute should apply its extensive experience in kinematic GPS research to the existing photogrammetric system. 
This paper presents the most recent system developments and details the bundle estimation analysis undertaken to 
investigate performance. Finally, details are given of the current work and future plans. 
1. INTRODUCTION 
An efficient road network is essential for a country's 
economic activity. Therefore, it is necessary to minimise 
any effects of maintenance and expansion programmes. 
Around ten years ago, Photarc Surveys Limited of 
Harrogate UK decided to address the problem of using 
traditional terrestrial survey techniques to provide 
essential highway profiles. A non-contact 
photogrammetric system was conceived and developed 
to provide the necessary data without disturbing traffic 
flow. 
A Zeiss UMK 10/1318 Universal Camera is 'cradled' out 
of the rear door of a Bell 206B Jet Ranger helicopter to 
capture images of the highway from a typical altitude of 
75m. Single model analytical analysis is then utilised to 
give regular grids of road spot heights to RMSE +0.005m 
using control points surveyed at 40m intervals along the 
hard shoulder of the highway (Smith and Joy, 19953). 
Further details of the system's development program and 
proven performance is dealt with in Boardman (1994). 
Despite the ability of the system to provide clients with 
cost effective profiles, the requirement for full ground 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996 
control along the hard shoulder is undesirable both for 
financial and safety reasons. The Institute of Engineering 
Surveying and Space Geodesy became involved in late 
1993 with two distinctive aims. These were, firstly, that 
aerial triangulation should be applied in the analytical 
analysis to quantify the potential for reducing ground 
control. Secondly, that the Institute should apply its 
extensive experience in kinematic GPS research to the 
existing photogrammetric system. 
2. PRELIMINARY CONSIDERATIONS FOR 
HELICOPTER PHOTOGRAPHY 
The use of aerial triangulation and GPS have been 
investigated by many eminent researcher's with respect 
to fixed wing aircraft photography and it is not the 
intention of the author to retread this ground. However, 
the use of low altitude helicopter flight is more novel and 
such an investigation had to consider the unique 
operational characteristics of this aerial platform (Hansen 
and Joy, 1995). Preliminary theoretical analysis showed 
that to achieve the +0.005m heighting precision level, 
GPS derived perspective centre coordinates would be 
required at RMSE Z=+0.007m (height). This is very high,