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Since the terms "fully automatic", "semiautomatic" and
"automatic" are used in different ways in the context of aerotri-
angulation, we should like to define them at this point:
Fully automatic measurement is the image point measure-
ment without any human interaction.
Semiautomatic measurement is the automation-aided image
point measurement with human interaction.
Automatic or automated measurement is the summary of
fully or semiautomatic image point measurement.
Further definitions:
New point is a point, which lies in a very distinct position in
the images and is chosen and measured by a human operator.
Its three-dimensional object coordinates will be kept after the
block adjustment for further uses.
Tie point is an image point, which ties the neighbouring im-
ages together. In PHODIS AT, tie points are usually deter-
mined by the fully automatic measurement procedure.
Aerotriangulation by PHODIS AT can be broken down in 4
steps:
* Block preparation,
* Block measurement,
* Block adjustment and
* Block post-processing.
These steps are described in more detail in the following.
2 Block preparation
Block preparation takes a lot of time with the currently used
and feasible aerotriangulation methods. Points have to be pre-
identified with the help of image prints. Point numbers have to
be assigned, and the points have to be marked for transfer,
often by means of a point transfer instrument.
These procedures are omitted completely by PHODIS AT.
The following data and information are required for the block
preparation in PHODIS AT only:
* scanned images with a resolution ranging from 7 um to ca.
60 um,
* per image: the image number, the flight number if neces-
sary, the approximate projection center and the flight di-
rection,
* camera protocol, and
* ground control information.
The approximate projection centers can be derived either from
the log file of a flight planning system such as T-FLIGHT, or
simply by taking the data from the image center plan. Of
course, they can also be taken from program systems, which
derive the projection centers from GPS flights. GPS data pro-
vide precise information on projection centers but are abso-
lutely not a prerequisite for aerotriangulation measurement by
PHODIS AT.
With the help of the above information, PHODIS AT creates a
graphical block display, computes the approximate overlaps
and determines the normal and crossing strips of the block.
The link between the flight and image numbers and the image
files is also established. In this context it is irrelevant if the
computer has direct access to the image files or not.
Because of the large amount of data per image (cf. Table 2) it
may be assumed that the computer does not have direct access
to all images of a block. This is why PHODIS AT allows sub-
dividing the whole block in subblocks of any size, which can
be processed individually and adjusted together later on.
During the definition of subblocks, care should be taken to
ensure that they overlap each other by at least one image strip
so that the subblocks can be tied.
Table 2: Memory space required for black/white images
m on Data volume for 100 images incl. pyramids
Ty 144 GB
14u 36 GB
28 u 9 GB
56 u 2.3 GB
If the image data are stored in compressed form, the data vol-
ume can decrease considerably depending on the selected
compression factor. However, the file access will be slowed
down because the data have to be decompressed during each
access operation or the data of the whole subblock have to be
decompressed before measurement.
For each subblock, the following operations for the block
measurement can be performed automatically:
* Loading of the images of the subblock after removing a
previously loaded subblock. For this reason, each image is
assigned its own loading and removing procedure.
* Generation of image pyramids, if not available.
* Fully automatic or manual interior orientation if not yet
done.
All preparatory work is supported by graphical user windows.
They are very easy to use and monitor. Here, the block display
(Figure 1) is of particular interest and supports the following
functions:
* Schematic display of the block, where the whole block
structure is represented by square-formed image symbols,
* Subblock selection, where an arbitrary subblock can be
formed by clicking the image symbols to be included,
* Display of the block overview and zooming in and out part
of the block,
e Optional display of image icons, image numbers and inte-
rior orientation results, and
e Selective turn-on or -off of individual strips.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996