ytical
with mass storage devices which allow the storage of a
whole stereo model. On this base, the Transputer slot
system was developed, as schematically shown in fig.
6. It works as a peripheral system in connection with a
Vax computer. Currently, 25 Transputers T800 are in-
tegrated into the system. All processes of image corre-
lation are implemented on these processors, whereas
the determination of the normal equations for the
computation of the finite elements is carried out by
the host computer. The computer capacity of one
Transputer amounts to about 3 Mips and corresponds
to the processor power of a Vax processor 3200; the
whole system has a 'theoretical' computing power of
75 Mips.
Host computer
21”, 10 Transputer card with frame buffer
Master transputer
Disk 0 Disk 1
=. lo
al bo 2 2 Di 1
1 3
Slave transputers
0 0 Jo
1 4 1231 9115 3 14231, 2
3 2 1 1 1
2 3 0 0 0
0 6 3 2 7 0 3 8 2 3 9 2 3 10 2
1 1 1 1 1
0 0 0 0 0
31 4 pD—3] 3 15 [£—3] i4 2—3] i5 I2.
1 1 1 1 1
0 0 0 0 0
3 16 2 4 17 2 d 18 2 3 19 2 3 20 2
1 1 1 1 [1
: Ru
[s]: T oet
0 0
Disk 3 Disk 2
Fig. 6
Configuration of the Transputer Slot System with a
distributed mass storage system.
547
4.3 The verification system
Verification is a very important part of an automated
process. The way to control the results of image corre-
lation and of the data editing has already been dis-
cussed in paragraph 3.6. This work is currently done
on the DSRI5, equipped with the image injection sys-
tem Kriss. In principle, these operations can also be
carried out on a digital plotter; however, one may ask
if the same efficiency can be obtained as with an ana-
lytical plotter. The development work on the injection
system has shown that the image definition on a mon-
itor, even with 1'500 x 1'200 pixels, is still considerably
lower than in the oculars of an optical system. A
rough estimation of the resolution of an optical obser-
vation system shows that this corresponds approxi-
mately to a performance of 3000 x 3000 pixels, and this
being done in stereo. Consequently, the analytical plot-
ter will still play an important role for photogrammet-
ric production, especially when a great amount of data
has to be processed.
4.4 Output of image data
An important by-product of digital photogrammetry is
the generation of orthophotos. Up to now, orthopho-
tos have been produced on special orthoprojectors, by
optical transformation procedures (cf. the Leica OR1 or
the Zeiss Orthocomp). The digital processing of data
should allow a considerable increase in quality accord-
ing to the experience of the printing industry. The
image could be reproduced on the basis of photograph-
ic procedures or on the basis of ink-jet or laser printers.
The advantage of ink-jet printers lies in the possibility
of reproducing a very limited number of copies. It
would then be possible to produce orthophotos on re-
quest, whereas photographic procedures are less flexi-
ble. Digital reproduction should also considerably fa-
cilitate the layout of the orthophotos, including the
lettering and eventual cartographic editions.
The large-format raster plotters like those used for col-
or copiers or special ink-jet printers should largely ful-
fil the quality requirements. The printing time can be
considerably longer than the scanning time, as only a
limited number of pictures have to be reproduced. The
quality of the orthophotos should correspond to a pho-
tographic reproduction with an enlargement of about
10 x (cf. table 3).
Image format AO, possibly A1
Ink-jet or color laser printer
Resolution ^ 100 points /cm and color
with varying point size
(equivalent to 1000 dots/inch
for a fixed point size)
Printing time for AO < 30 min.
Table 3.
Requirements in the image output.
