NEW AUTOMATED PROCEDURES
FOR CREATING LARGE SCALE DIGITAL ORTHOPHOTOGRAPHY IN URBAN AREAS
John A. Thorpe
Chairman and Chief Technical Officer
Wolfgang Schickler
Manager Advanced Technologies
Analytical Surveys, Inc., Colorado Springs, CO, USA
e-mail: wolfgang@anit.com
Commision IV, Working Group 4
KEY WORDS: Automation, Digital Elevation Models, Orthoimages, Production
ABSTRACT
With the increasing demand for high-resolution ortho imagery of urban areas in the U.S. comes a need for faster and less
expensive production methods. At ASl's Advanced Technologies Division (ATD) a completely new production system is
being developed, using precise flight management systems, airborne GPS,an inertial measurement unit, automatic camera
exposure, precision 60% sidelap photography, automatic film scanning, automatic interior orientation, automatic aerial trian-
gulation, automatic DTM capture with minimal editing, orthophoto production and final image mosaicking into a seamless
database. Although more powerful computers and extensive mass storage devices are required to handle the greatly increased
computational load, the resulting decrease in total operator-hours and production schedule is considerable.
1 INTRODUCTION
1.1 Motivation
Automatic orthophoto production requires several compo-
nents; a scanner and a plotter for digital input and output,
a digital elevation model (DTM) and information about the
interior and exterior orientation of the images to be rectified.
Up to now, most of the components need human interac-
tion to be performed. The most time consuming parts are
the aerial triangulation! and the data capturing for the DTM
generation. Besides others, the automation of these two com-
ponents are the major objectives of the current ATD research.
This paper documents the progress we have made so far. An
overview of the whole system shows the combination of the
individual components. First results of the development and
test of some of the components are presented.
In this paper the results are given for 1:10,000 photography,
a scale commonly used in U.S. for digital orthophotography
of urban areas.
1.2 Overview
The objective when doing the image capturing is a GPS-INS
guided flight mission resulting in very precisely positioned
6096 lateral and 6096 longitudinal overlapping imagery.
Figure 1 shows this configuration.
The main advantages of this flight configuration are as fol-
lows:
1. The Airborne GPS guided flight guarantees very pre-
cisely pre-planned exposure points. The processing of
the GPS-INS navigation data captured during the flight
results in very good approximate exterior orientation
values for each image. These approximate values are
lin the case the density of available control points is not high enough to
perform individual spatial resections for each image
5 01123125 134
Figure 1: Configuration of 60% lateral and 60% longitudinal
overlapping imagery
accurate enough to directly apply an automatic aerial
triangulation.
2. The 60/60 photography enables us to get a view from
four different perspectives of the ground in between
buildings, respectively four different perspectives of the
ground. This is essential when doing automatic DTM
generation in urban areas. This is a very promising ap-
proach in separating built-up objects from the ground.
3. With 60/60 photography, only the central 40% by 40%
(plus a small overlap) is used for the final orthopho-
tography. The resulting imagery is very high in quality
due to minimal "building lean” (radial displacement)
and excellent matching of radiometric values.
4. Note that although nearly twice as many images must
be captured, the resulting savings from scanning di-
rectly the negative film (no diapositives are needed),
automatic interior orientation, aerial triangulation and
semi-automatic DTM capturing more than compensate
868
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
