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The high degree of flexibility built into the user interface
allows a highly automated mensuration procedure. A
flexible window-based image display of multiple images
provides the efficient transfer and measurement of points
in multi-overlap regions. The use of autocorrelation for
this type of mensuration provides a high degree of
reliability. While in mensuration, the easy accessibility of
the numerous image enhancement and image
manipulation functions greatly assist the operator in
performing the measuring process. All these factors
provide a measurement system that can be used with
relative ease (Madani, 1996).
Some of the main features of ISDM are as follows:
e Project, camera, strip, photo, and control creation
and editing
e Mono- and multi-cursor measurement
e Interactive/automatic mensuration capability
(autocorrelation and least squares refinement)
e Interior, relative, absolute, singe photo resection,
and simultaneous bundle adjustment
e Image manipulation and image enhancement tools
e Sophisticated but easy to use image point selection
and editing tools
e User selectable statistical indicators and blunder
detection methods
e Graphical symbols for points and status of
mensuration process for each point
2.4 MATCH-AT (Automatic Aerial Triangulation)
MATCH-AT is a complete automatic aerial triangulation
program system (Krzystek, et. al., 1995). MATCH-AT
performs hierarchical multi-image matching of cluster tie
points in the standard (Gruber) locations.
This program is mainly divided into two parts. In the first
part, the user provides geometric information about the
block of aerial photographs, such as camera data, flying
height, amount of endlap and sidelap, and image
sequence in the block. Additional information, such as
exterior orientation parameters derived from navigation
systems (GPS and INS), a crude DTM data, or a
combination of both, can also be used to compute
approximate locations of all tie points areas with
sufficient accuracy. In the absence of such information,
MATCH-AT uses an integrated DTM generation which is
applied in the upper levels of the image pyramid (for
instance, 960 um and 480 um) in combination with the
block adjustment. The tie point areas are updated in
each image pyramid level using the coarse block DTM. A
method which uses an automatic relative orientation for
all image pairs is kept in reserve for critical situations
that are imprecise initial orientation parameters. The
second part uses the approximate locations of tie points
to generate feature points using a multi-image technique.
Finally, a simultaneous bundle adjustment is carried out
on the matched tie points to compute exterior orientation
parameters and 3-D coordinates for all ground points.
This new version of the MATCH-AT program was tested
on the OEEPE test block FORSSA (4 strips of 7
photographs scanned at 30 um resolution), and a
computational time of about 4 minutes per image and a
EINBETTENO, value of 0.33 pixel size were achieved
(Heuchel et al., 1996).
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996
3. DIGITAL AERIAL TRIANGULATION RESULTS
The process of digital aerial triangulation (semi-
automatic and automatic) may be divided into three
steps:
a) Preparation and Project Setup
b) Measurement and Orientations
c) Bundle Block Adjustment
3.1 Preparation and Project Setup
In this step, all photographs of both projects were
scanned by PhotoScan using its “Photo Alignment”
option at 15 resolution. The Photo Alignment option
allows for precision interactive/automatic measurements
of fiducials or reseau points prior to the digital image
collection. A full set of overviews (6 overviews) for each
image was created and then compressed by a JPEG
board (available on both the PhotoScan and the IMD
systems). Overview creation and image compression
were done in a batch mode. The turn-around time for
scanning at 15 um pixel size, for creating a full set of
overviews, and for image compression was about 15
minutes per photo.
The Project Management utility of the ISDM product was
used to set up the Texas and the Maryland projects.
Camera data, control points coordinates, and other
parameters relevant to these two projects, such as image
refinement flags, orientations, and bundle adjustment
tolerances were also entered.
3.2 Measurement and Orientations
Digital triangulation operation by ISDM is done in two
steps: Interior Orientation (IO) and Relative Orientation
(RO) and Point Transfer.
The fiducial marks of one image from both projects were
measured manually. Then, automatic IO was performed
on all remaining images. The overall performance time
for measuring 8 fiducial marks and applying an affine
transformation was about 1 minute per image, including
editing and remeasuring observations, if necessary.
Before performing a relative orientation, a suitable tie
point pattern can be created using the Project
Management utility to generate a well distributed image
point configuration. This option was not really necessary
due to the fact that the Texas block had at least 12
signalized points on each image, and the Maryland block
had 5 to 7 pugged points on every other photograph.
Nevertheless, it helped to locate these points very quickly
and to measure additional tie points.
The ISDM product has a very flexible procedure for
performing a semi-automatic relative orientation and
point transfer. The procedure used in this study is as
follows:
a) Measuring First Model in a Strip
e Set proper auto-measurement flags on.
e Measure manually center points of the stereo pair.
