MULTI-RAY MATCHING FOR AUTOMATED 3D OBJECT MODELING
Jolyon D. Thurgood“, Michael Gruber”, Konrad Karner“,
à Vexcel Corp., 1690 38" Street, Boulder CO, USA — joe.thurgood@vexcel.com
° Vexcel Imaging GmbH, Münzgrabenstrasse | 1, Graz, Austria — mgruber(@vexcel.co.at
VRVis Research Center for Virtual Reality and Visualization
Inffeldgasse 16, Graz, Austria - karner@icg.tu-graz.ac.at
Commission I, WG HI/2
KEY WORDS: Digital Aerial Images, Multiple overlap, Object reconstruction
ABSTRACT:
Traditional photogrammetry exploits stereoscopic image measurements to reconstruct the shape of objects. This technology is well
known and understood for over a century. Since the age of the stereo comparator human operators have been able to recognize th
depth of a scene with remarkable accuracy. In principle, this has not changed during the time that image processing has beei
introduced into the photogrammetric production chain. Only a certain degree of automation has been derived, when matching and
image correlation has replaced the human eyes.
Nevertheless, we need to confess that shape from stereo is not very robust and that a time-consuming and therefore expensive control
and verification process is needed after the automated reconstruction process.
To overcome such problems, we argue that a process based on multiple image overlap is the appropriate solution. In the age of
digital aerial cameras such multiple overlaps can be commanded without extra costs for additional images. A forward overlap of at
least 80 % supports a robust and highly redundant measurement. Automation and verification starts to become an easy job, and based
on the level of redundancy, we can expect a much more reliable means of automated production.
In urban areas we have an additional benefit in the reduction or elimination of occlusions.
In this paper we present several examples of multiple image matching, based on images taken with the new large format digital aerial
camera UltraCam-D from Vexcel Imaging
1. INTRODUCTION
Aerial Photogrammetry has developed a number of rules and
guidelines to successfully plan and carry out an aerial photo
mission. Most prominent among others is the 60%-20% layout
of flightlines, which has not changed over several decades. Pros
and cons of such a layout are well known, but in fact we must
confess that it is meets only the minimum requirement for any
photogrammetric production,
By moving to a fully-digital approach, photogrammetric
practicioners may rethink such old rules and ensure that a
possible added value of new production schemes will find their
way into the final products.
In this contribution we want to focus on the digital aerial
cameras which have emerged during the last few years. We are
convinced, that such cameras have the potential to renovate and
rejuvenate the photogrammetric production chain and to add
value to the final image-derived product, be it a higher degree
of automation in successive parts of the production chain, a
more complete documentation of the project area and its
objects, or just as importantly the ability to enhance robustness
or even accuracy.
2. FROM ANALOG TO DIGITAL
Photogrammetry has its source in the all-analog world. Films
(or even the glass plate) have served as the medium for image
information, and mechanical instruments were used to collect
vector data. The transition from the analog to the digital
workflow was long and inhomogeneous, starting at the end of
the production line — namely the recording of three-dimensional
vector data into a digital CAD system. The last step — the initial
digital recording of the source image data — is now in progress.
Such a long evolutionary process may bring out a number of
hybrid solutions, which may have their benefit in commercial
application. This was the case in photogrammetric operations,
e.g. when analog stereo plotters were modified to become
analytical or when the orthophoto-projector was developed at a
time when images could not yet be scanned.
The benefit of a digital workflow was first proclaimed at a time
when the handling of large datasets (e.g. digital images at a file
size of up to 500 MByte) was cumbersome or expensive. This
has changed during the last few years and photogrammetry is
finally now able to exploit such products of the IT industry
which show rapid processing, huge data storage capability and
fast data transfer rates.
More and more the accessibility of such an IT infrastructure has
shown its impact on photogrammetric production and more and
more softcopy photogrammetry has become the rule — even if
the digital images are produced through use of a precision
scanner after a traditional analog photo flight. This is finally
changing, driven by the advent of the large-format digital aerial
camera.
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