oints
ints
of the interior
tor. Again the
1e planetarium
h the help of
rojectors (as
the reference
the pole), and
neasured. The
a local system
otogrammetric
inly faster and
of the required
ditions in the
ires of suitable
assumed to be
by the speci-
ot remeasured
finition of the
tion system) a
the measured
| the order of
ctness of the
jh the pole we
XY-coordinate
| we select a
ed points can
ystem (the so-
om).
orientations of
fied way. The
are treated as
t the principal
S we know for
ck points) the
> slide (image)
e the principal
projection of a
- are visually
per and lower
ES
ctification that
ction 4. Firstly,
the slide plane
r this grid is
‘ace and then
further to the respective camera position. The result is a set
of eight distorted grids. In a similar way we obtain eight
masks (one for each projector) by projecting the mosaic
boundaries from the dome surface to the slide. A mask
image is black in areas outside the respective region of
interest, it is white within the area of interest and it shows a
transition zone (from white to black towards the region of no
interest) in the predefined overlapping area. The grey
shades may be interpreted as weights for the image
contents with white being 1.0 and black 0.0. Note that the
mask image is not a binary image as it may currently
contain any decimal value between 1 and 0 (the term "gain
mask" might be a more appropriate name). Additionally the
mask image should also contain tiny marks in the corners
intended to facilitate exact positioning of the films in the
slide frames (see figure 8). The full set of grids and masks
remains the same for any panorama rectification as long as
the camera for and the way of data acquisition or the
projectors have not been changed.
The software for resampling can easily be installed through
IDL® The operator, who needs not be an expert neither in
computer science nor in photogrammetry, just has to
measure the "fiducial marks" (usually the border lines) of the
original images for the restitution of the interior orientation of
Area of no interest
Area of interest | y
Transition areas
oe ve à Slide marks 4. —
Figure 8: Example of a mask image
the cameras. After defining the order of the images the
rectification process commences to run automatically. The
resampled images are merged with the mask images by a
simple pixel-by-pixel multiplication thus yielding the final
slide images. These digital images need to be plotted to film
via a slide writer. The final crucial step is the mounting of the
films in the frames. Special register frames together with the
previously mentioned slide marks facilitate the accurate
mounting of the slide films.
113
The generation of a test panorama that contains a dense
"geographical" line grid of the dome is highly recommended
as it seems to be very helpful for checking the actually
achievable accuracy. The linear features are quite sensitive
to small geometric irregularities and allow a rough
estimation of the overall precision.
7. CONCLUDING REMARKS
The panorama generation as described in this paper is a
prototype and might be adjusted and augmented in one or
the other way. Particularly the radiometric adjustment as
mentioned in section 4 might be useful when dealing with
rather dark pictures and could be easily implemented
through the mask image. On the other hand and more
importantly there is a need for automatizing the process of
generation from data acquisition to film writing. The
acquisistion of digital images is one limiting factor that could
be overcome by employing digital cameras (such as for
instance the Kodak DCS 460) or by recording the pictures
on photo CD after development (currently by far the
cheapest choice). In the latter case one must be sure that
the interior orientation can be restituted. Usually the
standard process of generating the photo CD does not
digitize the image borders and, therefore, cannot success-
fully be used with non-reseau cameras. Fortunately non-
standard professional digitization delivers appropriate
images. The process of resampling can be performed at
any state-of-the-art PC and does not cause problems at all.
For the time being a more severe limitation is the writing
process of digital slides. Though some copy shops offer this
service there is still no guarantee that the pictures are
written geometrically identically at any time. Experience
showed that, after servicing the slide writer, the geometric
properties are likely to have changed slightly as far as shifts
of the origin and affine distortion are concerned.
8. REFERENCES
Kager H., 1989: ORIENT: A universal photogrammetric
adjustment system. 3-D Measurement Techniques.
Wichmann Verlag, Karlsruhe. pp447-455.
Kraus K., 1992: Photogrammetry Vol 1, Fundamentals and
Standard Processes. Ed.4, Dümmler, Bonn.
Kraus K., Schneider W., 1988: Fernerkundung Vol 1,
Physikalische Grundlagen und Aufnahmetechniken.
Dümmler, Bonn.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
