The function of a digitizing card is to monitor the status of the 
encoders and ancillary devices (such as Foot Switches) in the 
instrument. Should there be a change in the position of the 
microscopes (4-Axis) or the model stage (3-Axis), the digitizing 
card will register the new position(s) and send the new data to the 
interface software system. 
Digitizing cards are extremely reliable and requires no User 
maintenance. Of the hundreds of systems ISM has delivered, 
only 2 cards had been returned as damaged. In one case the 
cause was a severe lightning strike to the building which had also 
damaged several computers. The other was found to be short 
circuit due to User mishandling. In any case, should a malfunction 
ever occur, replacement can be delivered readily via air courier 
without undue delay. 
5.0 INTERFACE SOFTWARE & GRAPHIC SYSTEM 
The interface software for a digital up-grade typically includes 4 
major components: 
- afacility for the orientation of the stereo model, 
-  afacility for numeric data output, 
-  afacility for graphic data output 
-  agraphic system. 
In the ISM SysteMap Digital Mapping Software, the orientation 
module accepts either photo or model coordinate input. In the 
model coordinate mode, it provides computer assisted Absolute 
Orientation. In the photo co-ordinate mode, it provides Interior 
Orientation facility as well. In both cases, the User must first 
perform Relative Orientation. This facility establishes the Matrix 
which is used to transform the encoder signals (X, yx" y" or x,y,z) 
in real-time into ground coordinates (X,Y,Z) for the numeric or 
graphic data output facilities. 
The facility for numeric data output may support tasks such as 
mensuration for aerial triangulation. The system may output photo 
coordinates (only in the 4-Axis case and in stereo comparator 
mode), model coordinates (after Relative Orientation has been 
performed) and ground coordinates (after Absolute Orientation 
has been completed). 
The facility for graphic data output is essentially a "driver" for the 
graphic system. The Driver directs and inserts ground coordinates 
(X, Y,Z) into the graphic system which generates map symbology 
that constitute a digital "manuscript". 
Graphics systems that have been used in Analog Instrument 
upgrading include Intergraph IGDS, Synercom, Atlas, Kork, 
AutoCAD, Intergraph MicroStation, CadMap and others. ISM 
SysteMap utilizes MicroStation exclusively. 
6.0 DIGITAL CALIBRATION 
ISM provides digital calibration of up-graded instruments. The 
methodology published by Prof. Klaus Szangolies (1966) is 
utilized. The calibration data is recorded directly from the encoders 
and a 15 point (3 x 5) stereo grid test is performed. 
84 
ISM utilizes an in-house software system to indicate the 
adjustments necessary, to record the observations, to perform the 
calculations, to generate the model deformation diagram and to 
generate the horizontal and vertical accuracy ratings of the model. 
This kind of calibration is particularly important because a modem 
digital map is essentially a "positional" file of mapped features. 
The Positional Files together with the Digital Elevation Model 
(DEM) are the data base from which cartographic representations 
(eg. contour map) are derived. A structured Positional File is also 
a primary source of data for a Geographic Information System 
(GIS). The positional accuracy, which is entirely dependent on the 
instrument accuracy, cannot be over-stressed. 
7.0 FINANCIAL CONSIDERATIONS 
A complete budget for instrument up-grading must include the 
following elements: 
a. Instrument cost 
The capital cost of the instrument may justifiably be 
overlooked by some businesses with long term ownership 
of instruments. The cost of instruments has often been 
fully recovered or completely depreciated within the 
financial structure of the business, however if an 
instrument has to be acquired, then the combined cost of 
2nd-hand purchase, packing/removal, shipping, 
installation/overhaul and calibration cannot be overlooked. 
b. Encoding cost 
Even if the encoding process has been greatly simplified 
by ISM, a significant cost still remains. If the instrument 
has been factory encoded, the cost is far less as 
replacement encoders are relatively inexpensive. 
c. Computer cost 
Fortunately, Mini Computers or Workstations are no 
longer mandatory. in instrument up-grading. Personal 
Computers are the dominant choice. A basic PC may be 
fairly cheap. However, a system with good CPU speed, 
RAM, adequate Hard Disk Drive, and large monitor is still 
a cost consideration. 
d. Software cost 
A complete digital mapping software system will comprise 
of an instrument interface system, a graphic system, 
TIN/CIP programs for the DEM and ancillary system for 
data integrity checking/repairs. The total cost of a 
complete system is not inexpensive. 
e. Installation and training cost 
À major budget item is the fees and expenses payable for 
the installation of the instrument/encoding system and 
computer hardware/software system. The fees payable 
on software training can also be substantial. 
Often, À User will presume that self-training is possible, 
however this assumption would be false economy 
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