Digital Photogrammetric Applications
with the
Prime-Wild S9 Analytical Plotter
David Wilkins
Institute of Geodesy and Photogrammetry
Swiss Federal Institute of Technology
ETH - Hönggerberg
CH - 8093 Zürich
Switzerland
Abstract
In the context of a collaborative project currently underway at the Institute of Geodesy and
Photogrammetry of the Swiss Federal Institute of Technology (ETH) in Zürich, a Prime-Wild
System-9 Analytical Plotter (S9AP) has been modified to enable the installation of a pair of CCD
cameras. Together with appropriate image acquisition hardware and host computer, the S9AP is
thus transformed into a general-purpose image scanner for digital photogrammetric applications.
Before the instrument can be used as such, it is necessary to perform a calibration to determine the
relationship between the digital image pixel coordinate systems and the S9AP stage coordinate
systems. An extensive software package has been written for this, which contains some special
components made necessary by the mechanical design of the instrument. As a means to
demonstrate the potential accuracy of the system, the signalised points of a photogrammetric test
block were digitised, their coordinates determined by template matching and subsequently
processed in a bundle adjustment. The results of this investigation are presented, together with a
comparison with the results from a manual measurement of the same block on the same instrument.
Key words: analytical plotter, digital photogrammetry, image matching, bundle adjustment.
1. Background
The aims of this paper are twofold. It arises out of
the work done over the last two years on a
collaborative project between the Institute of
Geodesy and Photogrammetry of the Swiss Federal
Institute of Technology (ETH) in Zürich and Wild
Heerbrugg. The purpose of the project was to
develop a system for automatic DTM data
generation through image matching, using the
analytical plotter System-9 AP (S9AP) as an on
line source for analogue image information. To
this end, an S9AP with an adaptation to its optics
allowing the attachment of a pair of CCD cameras
was installed in Zürich. The work on the project
then followed two major paths: calibration of the
hardware and algorithms for the image matching.
The first aim of this paper is to present the result of
the former, that is, to introduce the modified S9AP
as a general-purpose image scanner.
The second aim is to present one possible
application using such a system - aerial
triangulation using image coordinates determined
by point location in digital images. This lies
outside of the specific aims of the project, but it has
always been seen that the modified S9AP could
have applications in other areas; the overall aim is
to show this.
The paper is organised into two parts reflecting
these dual aims. The first part (sections 2 and 3)
will describe the system hardware, the procedures
for its calibration, and some results therefrom. The
second part (section 4) will concentrate on the
aerial triangulation investigation - the data
acquisition and the results of bundle adjustments
thereon.
2. Hardware Introduction - the S9AP
2.1 Analytical Plotters as Image Scanners
Since analytical plotters became generally accepted
in the commercial sector in the early 1980’s, there
have been various attempts at installing them with
CCD cameras to enable the digitisation of image
sub-scenes. In the most cases, the subsequent
processing of the digital imagery was aimed at, but
not restricted to, the automatic or semi-automatic
generation of height data for DTM applications.
Two of the major photogrammetric instrument
manufacturers ran projects along these lines. Zeiss
Oberkochen of West Germany, in collaboration
