DIGITAL CLOSE-RANGE PHOTOGRAMMETRY 
USING ARTIFICIAL TARGETS 
F.A. van den Heuvel, R.J.G.A. Kroon 
Ingenieursbureau Geodelta, Oude Delft 175, 2611 HB DELFT, The Netherlands 
R.S. Le Poole 
Sterrewacht Leiden, P.O.Box 9513, 2300 RA LEIDEN, The Netherlands 
Abstract 
A procedure for an automatic search and measurement of artificial targets in digital images for close-range 
photogrammetric applications is presented. Photographs taken with a semi metric 6x6 camera were digitized 
by the "ASTROSCAN" at the Sterrewacht Leiden. The especially designed targets contain a circular barcode 
for automatic identification. It is shown that this procedure improves both precision and productivity of the 
photogrammetric process. 
Key Words: Close-range Photogrammetry, Image Matching, Image Quality, Scanner 
1. Introduction 
The objective of this study was the development of 
a fully automated procedure for close-range 
photogrammetry. An increase in productivity and 
improvement of precision will make 
photogrammetry even more attractive as a three- 
dimensional measuring technique. 
The procedure developed by Ingenieursbureau 
Geodelta and Leiden Observatory (Sterrewacht 
Leiden) of the Leiden University consists of the 
following steps: 
- digitalisation of photographs; 
- digital search for the images of the targets; 
- estimation of target positions in the images; 
- reading the identification of the targets found; 
- performing a bundle adjustment to arrive at 
three-dimensional target coordinates. 
To test the procedure developed, a set of eight 
photographs was taken from a targeted indoor 
scene. À 6 x 6 cm semi-metric camera with black- 
and-white negative film was used. For comparison 
the photographs were measured in a conventional 
way as well, using a Kern DSR 11 analytical 
plotter. The bundle adjustment showed an 
improvement in precision of the result obtained by 
the automatic procedure relative to the precision 
obtained through the conventional 
photogrammetric procedure. 
For the automation of the search, as well as for the 
identification of the targets found, the design of the 
targets plays an important role. 
2. Target design 
The targets were designed to facilitate automatic 
detection and identification. The target design 
consists of a white circle with a concentric ring on 
a black base. Around this there is another 
concentric ring in which a ten bit target 
identification is coded. The central circle is slightly 
oversized and has a small black dot in the middle to 
facilitate manual measurement. The rings are sized 
to allow for a realistic amount of defocus without 
losing the contrast to a significant extent. Sample 
targets are shown in figure 1. 
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figure 1: two artificial targets