4 Parallax Bar with Floating Mark
The VM operation is based on the floating mark prin
ciple using an automated parallax bar. The floating
marks are illuminated dots of 75, 125, 250 or 500
/im diameter on plastic disks in direct contact with
the photographs (separated by a 7 mil thick Mylar
protective marked cover). This approach emphasizes
the measurement on the photograph. Height measure
ment is direct and not subject to distortions. Most
of the time the photographs are in superimposition
with the map. However, to achieve optimal height
measurement accuracy it is possible to increase the
photomagnification beyond that required for super
imposition.
The parallax bar is motor driven in the X and Y
directions. X and Y parallax separations (px and
py respectively) are also motor driven using a single
4 dimensional joystick control. All four axes are
encoded: X and Y by rotary encoders with 50 /urn re
solution, py by rotary encoder with 5 jam resolution,
and px by a linear incremental encoder of 5 /am reso
lution to eliminate any backlash or linear to rotary
conversion errors. Assuming a nominal photobase of
100 mm the theoretical system resolution of measured
height is .005% of the flying height. With this
inherent capability of the instrument it is up to
the experience and training of the operator to
achieve repeatability and accuracy as near to the
theoretical as possible (Trinder, 1986).
Relative and absolute orientation parameters are
automatically converted into correcting motions of
the px and py stepper motor drives to eliminate y
parallax anywhere in the overlap area of the photo
graphs and to provide automatic height and elevation
correction for the various tilts and displacements
inherent in near vertical photography
5 VM Computer and Display
Computations of orientation parameters, correction
values for the motors, height and elevation measure
ments are performed by an Intel 8031 (8051 family)
microprocessor based system with approximately 45
kBytes of ROM based program memory. Programming was
done in Assembler language to achieve a maximum data
transfer rate from feedback elements to computing
and to the motor drives of px and py parallax motions.
The computer is housed in a control unit shared by
power supplies, encoding, joystick and motor control
circuitry. A separate Keyboard/Display unit is posi
tioned to the side of the operator (Fig. 2). It dis
plays at all times the photo X and Y coordinates
and a selected value or parameter (normally height
or elevation). The keyboard allows keying-in of
parameters, offsets, units, etc.
Figure 2. VM Keyboard/Display Unit
6 VM Output Capability (Printing)
Many users performing simple land use studies re
quiring the measurement of spot and object heights
may need no more than just a display of such heights
together with the corresponding X/Y photocoordinates
to be able to reconstruct the setup and repeat the
measurements.
Other workers require a hard copy of the jobs per
formed. For this purpose an 1/0 capability with a
dot matrix printer has been provided which on command
(pushbutton on the joystick assembly, Fig. 3) will
transfer a selectable and sequentially incrementing
observation number, height, elevation, and photo X/Y
coordinates to a printer for a permanent record.
Selecting another transfer mode allows a permanent
record of relative, absolute orientation parameters
and X, Y, Z control point photo-and ground coordinates.
Switches on the VM 1/0 board permit adapting the
printer output to a variety of popular printers.
Figure 3. VM Joystick Assembly with Transfer Buttons
7 VM Input/Output Capability (Computer Interface)
Via another output port, an RS 232 type serial 1/0
port, calibration parameters and running observation
numbers, height, elevation, X/Y photocoordinates may
be transferred to an external personal, micro-, mini
computer with its own RS 232 interface. Three push
buttons are provided on the joystick assembly to
initiate the transfer and to distinguish between con
tinuous, interrupted and termination of transfer.
The baud rate may be selected on DIP switches on the
VM 1/0 board and usually on DIP switches of computer
serial 1/0 boards. Alternatively computers may have
a software baud rate selection capability. The
availability of 300 and 1200 Baud selections enables
transfer of data via a standard modem. The VM is
normally connected as Data Terminal Equipment (DTE).
Conversion to Data Communication Equipment (DCE) may
be done by plug inversion on the VM 1/0 board.
The transfer of calibration and coordinate data to
Bausch & Lomb's own Resource Measurement System (RMS)
has been implemented. The data transfer rate is as
high as 9600 Baud at distances between VM and computer
of up to 30 m. Transfer to an IBM PC/AT computer is
also being undertaken. Data have been structured
into blocks of ASCII data and symbols according to a
logical compact data format. The data structure is
available to anyone wishing to interface to his own
computer.
8 VM - RMS Data Transfer
The RMS system uses a built-in Apple lie computer.
Operator friendly menu based software has been im
plemented to set up the RMS to receive either cali
bration data or coordinate data from the VM and to
store the data in files designated as "filename.cal"
or "filenam
Such disk t
as many as
data are av
sion, analy
ing to menu
9 Data Edit
The stored
ASCII forma
readable an
coordinate
Typically n
due to nois
operator er
in this eff
or profile
RMS CRT for
Transferr
dinates whi
coordinates
taining the
absolute or
known princ
(Manual of
Data anal
and perimet
ear feature
Internal
of RMS anal
(mean, vari
linear, mul
logarithmic
ANOVA, etc.
10 Data Pri
The data co
ed out on t
relating ob
values with
The RMS pro
generated b
of graphs.
11 Data Plo
Planimetric
coordinate)
or elevatio
Y*Y) profil
(DMP 40 or
sets. The
information
at the time
made on eit
overlays us
type plot m
relative to
ersed by a :
12 Conclusi
The combina
Bausch & Lo
measurement
as measurem
photograph
of a printe
powerful sy
low capital
maintenance
is in high
rather than
with the Re
RMS routine
38
