International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 5. Hakodate 1998 
DIGITAL CLOSE RANGE PHOTOGRAMMETRY DATA ACQUISITION SYSTEM 
WITH COMBINED GPS GEOREFERENCE AND ITS CALIBRATION 
Esmond Mok, Bruce King, Qing Zhu, Zhilin Li, Kent Lam 
Department of Land Surveying and Geo-Informatics 
The Hong Kong Polytechnic University, HK 
Commission V, Working Group 2 
KEYWORDS: CCD, Close Range Photogrammetry, GPS, Self-Calibration 
ABSTRACT 
A low cost digital close range photogrammetric system is presented for the acquisition of 3D surface information for efficient large 
scale and civil engineering mapping applications. Two GPS antennas are mounted together with two CCD cameras respectively on a 
stable bar and are employed for direct determination of camera position and azimuth during imaging process. This paper discusses 
the system calibration through a test field of control points. Some key issues about the integrated system such as the relationship 
between the GPS antennas and cameras and the achievable accuracy of the system are examined. The use of GPS geo-referrencing of 
the cameras, multi-station convergent imaging and simultaneous adjustment are stressed for improving the accuracy and reliability of 
3D surface data acquisition. 
1 INTRODUCTION 
Since small-format CCD cameras first attracted photogram- 
metrists’ attention in the mid eighties these cameras have 
evolved high-resolution, large-area CCD cameras with digital 
output. The increase in resolution has resulted in a demand for 
greater accuracy and precision requirements for geo-referencing 
the camera system. In order to reduce the number of necessary 
control targets, position and attitude can be determined by 
integrating other information such as GPS and INS data and 
applying functional constraints. Obtaining complete, accurate, 
and fast description of a 3-D object or environment may not be 
possible without such integration. 
GPS/INS systems has been successfully adopted in aerial 
photogrammetry for direct measurement of the exterior 
orientation parameters to decrease the amount of ground 
controls (Schwarz, 1995). Similarly, more sophisticated systems, 
and the methods for their integration have been developed for 
digital close range imaging (Li, 1997, Schwarz, 1996). Such 
research focuses on the areas of industrial and urban mapping 
applications. The system presented here is intended for the 
mapping of engineering sites, since civil engineering 
construction is a major activity in Hong Kong, and at present 
conventional mapping techniques are largely adopted despite its 
intrinsic inconvenience and danger on a construction site. It 
integrates the positioning technologies of GPS, photogrammetry 
and image processing. 
Using such an integrated system, the basic problem is just to 
determine the relationship between GPS and camera. This 
process is referred to as the system calibration. The adopted 
approach is that of self-calibration as reviewed by Fraser (1997) 
After briefly introducing the system configuration, a simple 
self-calibration model and DLT algorithm (Karara, 1989) are 
quoted directly. In the experiment analysis section, single- 
Stereopair and multi-image processing and the imaging 
configuration are addressed. 
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2 SYSTEM CONFIGURATION 
2.1 Cameras 
Two Apple QuickTake 100 digital cameras are employed. 
These cameras take 8 hi-resolution (640 by 480 pixels) 24-bit 
color images with a pixel size of 8.75 u m by 8.75 u m. Focus 
range is from 1.3m to infinity. The principal distance is 
approximately 8mm. 
2.2 GPS system 
Two Trimble 4600LS GPS receivers are used for camera 
positioning and one Trimble 4000SSI GPS receiver is used at 
base station for relative GPS positioning. 
This configuration of Cameras/tripods/GPS antennas mounted 
on a common stable bar is illustrated as in Figure 1. 
  
( GPS ) 
  
  
C camera ) 
Camera 
! 
i 
GPS ? d 
à 
camera 
GPS/Camera/Mounting bar Configuration 
  
  
9. 
  
Figure 1 System configuration 
3 SYSTEM CALIBRATION 
Because it is attempted to directly use the GPS and calibrated 
results for camera orientation and location in the future work, 
for convenience the self-calibration method is adopted in our 
experiment. The following issues need to be considered: 
1. The design, location and observation of the controls;