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The condition equation can be written as: Ay + By = f"
where v is the vector of measurement residuals, y are the corrections to
parameters which are initially given as approximate values, and f° are
misclosures using observed values. Formulated in this way, the
equation could be singular in a poor GCP configuration (Gugan 1987,
Westin 1990), mainly due to the high correlation between parameters
(mainly phi and platform motion). It could be stabilised by padding
with ‘fictitious’ equations, taking this shape
A 0 y B f^
where vp are corrections to approximate values of unknown
parameters. Simply, unknowns could be treated as fictitious
observations with associated weights. These weights are usually set
from experience and fine-tuned by trial and error. Using weights to
effect the stability articulated above, the solution by Mikhail (1976), if
Q is the apriori cofactor matrix for the measurements and Wpp is the
apriori weight matrix for the parameter estimates, is:
y - (BACAR BW BAGATY f°
v can always be calculated after a convergence has been achieved from
a few iterations.
V m. AMAGATY'(f BY)
3.1 Software
The need for simulations and analyses of an optimal SPOT system
required that this SPOT modelling software was developed. This has
been done in an analytical-plotter environment, with a specially
developed real-time system supporting profiling and image
superimposition.
The software has been developed under Microsoft Visual C++ system,
making use of this operating system’s substantial programming
resources driven by the Microsoft Foundation Classes (MFC).
Windows file serialisation system, for example, ensures data
permanence allowing a project to be continued exactly from where it
was stopped; on start-up the system automatically loads the last project
exactly where it was discontinued. The software has been programmed
towards Windows-NT compatibility and runs well under Windows-95.
3.11 Inner Orientation: The four corners of the image would
normally be used for inner orientation. Where analogue prints are used
in an analytical plotter it is now possible to use prints with specially
marked image corners for easier identification. The corners have image
co-ordinates of +39 em in both x and y as defined by the characteristics
of the SPOT panchromatic camera (3000 x 13um), and the image
centre has co-ordinates of 0,0.
3.12 GCP Management: This allows for input of both
geographical and Cartesian co-ordinates. The module supports several
possible choices of ellipsoidal parameters and map projection systems
for the input data and the output of results. It also provides for needed
transformations between the Cartesian, geographic, earth’s geocentric
and inertial geocentric systems.
3.13 Bundle Resection: A single image bundle resection is done
initially. If tie points are needed for a good relative orientation, they
could be measured after this computation. This initial orientation
assures that reliable approximate values for these tie points are
calculated. Linear array models are highly sensitive to the quality of
approximate co-ordinates attributed to tie points. After tie points are
measured, a two step adjustment is done, initially a single image
bundle adjustment of each of the two images, and finally with a block
adjustment of both images together. Typically, this bundle adjustments
takes about 20 seconds on a 486-50MHz PC.
4.0 THE REAL-TIME SYSTEM
The concept of the Leica Photogrammetric Workstation, which is
realized on SD2000 and SD3000 instruments as well as on upgrades of
DSR and Wild AC/BC instruments (see figure 2.0, refer also to Cogan,
Hinsken 1992 and to Hinsken, Meid 1993), is completely unchanged by
the implementation of the spot model. Mapping or GIS applications
work in the same way as they do with perspective models. Some of the
main characteristics of this Workstation are
- It is an open system, i.e. any application like mapping, GIS or
DTM collection on any compute platform may be connected to
it.
- All Leica analytical plotters can be controlled by the real- time
processor software (RTP) on the LMT computer: PDP- based
Kern DSR as well as DATA General- or UNIX-based WILD
AC/BC instruments can be upgraded to it;
- The real-time software on the LMT computer provides some
photogrammetric features and controls the superimposition
system without any duplication of real-time computations.
In addition to the perspective model, which had been originally
implemented, a new sensor model had to be introduced in order to
support a SPOT orientation software. This sensor model had to fulfill
the following conditions:
Figure 2: The Leica Analytical Photogrammetric Workstation
One of Three Stereo Viewers
Leica Mapping
Terminal !
(LMT) ı [Windows Application
under DOS , | Workstation (Host)
Mose
BC/AC- p——4
AVIOLYTL—]
Ü
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996
the mapping/GIS application interface had to remain
unchanged, i.e. applications must be enabled to receive
information and to control the instrument including
