mputer of
in object
type CCD
system. It
| with the
igh power
on in MS
to present
thods for
tem. First
pplication
. Possible
n cycle of
cording to
al-time,
ode (they
y factors.
acteristics
nich result
that were
well as
bilities of
ng frame
ach video
88). They
etrical and
sans they
practical
putational
tware and
ary digital
1s should
irge digital
accuracy,
sality — of
applications, and simultaneously, with possibly low
price.
2. DESIGN CRITERIA FOR CONSTRUCTION OF THE
LOW-COST SYSTEM
This concept consisted in elaboration of a recording,
digital data processing and measuring system based on
the so called, designed for these purposes frame
grabber card- a specialized electronic system-
constructed specially for a computer of PC type,
coupled with electro-optical CCD sensors and through
application of a proper control and photogrammetric
software.
Construction of a low-cost digital system for close
range applications having medium accuracy foresaw
realizarion of the following assumptions concerning the
hardware and software :
e the construction will be based on the IBM PC or
compatible computer, instead of a workstation,
e low-cost CCTV (Closed Circuit Television) - type
CCD solid-state cameras with video output (analogue
signal) of low or medium resolution will be applied to
this system,
e application of a frame grabber card, oriented on
digital elaboration in off-line mode in close range
photogrammetry,
e the system will be controlled from under user-
friendly Microsoft WINDOWS environment.
When converting the above tasks to practice, the
authors were fully aware of influence of these
assumptions on accuracy, reliability of results, speed
and degree of automatization of the process of
elaboration.
Design and construction of a low cost photogrammetric
digital off-line system, working in interactive mode for
close range applications was performed in the frame of
cooperation between the Chair of Photogrammetry and
Remote Sensing, Olsztyn University of Agriculture and
Technology and the Institute of Electronics, Technical
University of Lodz in Poland.
3. SYSTEM OVERVIEV
In this part of the paper, they way of working of the
basis hardware and software components of the
proposed system as well as characteristics of its utility
and functional properties.
3.1 CCD cameras
One of possible sources of digitized image acquisition
are electro-optical sensors with CCD matrix used as
converter. Advantages of the CCD cameras when
applied as visual sensors within structure of digital
system are undoubted (the most significant with regard
to the project realization are given) :
e considerable stability and precision of image space
geometry after digitisation,
e immutability in time of geometric deformations,
513
e correction of geometric and radiometric errors can be
performed with numeric means,
e possibility of application of a camera with
transmission of a composite video signal united with
pixelclock or of a camera with integrated A/D
converter together with direct transmission of digital
data.
In low-cost digital systems, industrial TV cameras are
in common use because of their relatively low price
(Luhman, 1991). They use standard video signal for
output of discrete information on grey levels of pixels.
Process of digitization of the analog video signal and of
the primary digital data from CCD matrix contained in
it, is unfortunately connected with creation of
geometric deformations of the image: the so called
effect of linejitter and change of the image scale as
well as with radiometric disturbances (Baltsavias, 1990;
Beyer, 1987; Beyer, 1988; Beyer, 1992; Lenz, 1990).
In this elaborated system we have decided, because of
financial respects, to use relatively cheap monochrome
solid state sensors CCD - Panasonic WV-BL204
cameras, with the European CCIR video standard norm
(Gruen, 1988). Transmission of the image is carried out
using composite video signal, or optionally with
external synchronisation. The CCD image sensor is of
the interline transfer modus and has dimensions of
6.4(H) x 4.8 (V) mm? which is equivalent to scanning
area of 1/2" pick-up tube. The CCD sensor's resolution
is 577(H) x 581(V) pixels with a physical pixel size of
11.1 um x 8.3 um. The Panasonic standard C mount
lens used for the project having focal length of 12 mm,
with focus range adjusted by camera and field of view
approximately 30 by 22 degrees, was recommended
for optimum performance.
3.2 Frame grabber
An integral part of the system architecture, determining
its technical advantages and quality is interface - frame
grabber card, which cooperates with computer AT bus.
Monochrome CCD camera interface (Figure 1) contains
16-bit graphic processor (TMS34010-40MHz)
dedicated for complex video operations e.g.: rotation
and mixing, etc. performed in real-time. The interface
mentioned here has been designed to co-operate with
modern dual-port memories what allows processor to
access the image memory while capturing data from
the camera. The graphic processor operates with
maximum speed at 40MHz clock rate, what ensures
the image processing in real-time, during its capturing.
The image processor operates using pipeline and cache
mechanisms. The local-bus architecture allows to
access the video memory by ADC circuitry. graphic
processor and host, respectively. A CRT controller
included to the graphic processor is a fully
programmable device, that makes possible to adjust a
system resolution to the application. In the realised
project 640x480 resolution is chosen to make
compatible capturing with PC-VGA display standard.
Higher vertical resolution of 480 lines per image is
used while camera works in interlace mode.
Sampling rate of video signal at 15MHz ensures the
square pixel and the proper image size on the screen.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
