Coordinate Recorders 
Most, if not all coordinate recorders on the market today, are based 
on a straightforward system design shown as a block diagram in Figure 1. 
Encoder pulses are accumulated in UP/DOWN counters, or alternatively the 
measured data is obtained in an absolute code. In either case, a sequencer 
or a multiplexer scans the counters and presents their contents one by one 
to transmission logic, which interfaces with the recording device. Point 
identification numbers and display devices are usually added; however, 
they are accommodated with the same design approach. 
A somewhat more advanced design is shown in Figure 2. Here the 
counters are replaced by an adder and a memory. A multiplexer or a se 
quencer looks at all input lines frequently enough to be able to pick up 
all pulses that arrive. These are then added to coordinate values in 
appropriate memory locations. The transmission of the data to the re 
cording device is from the memory. Even a very rudimentary memory can 
provide useful buffering and a basis for relatively simple addition of 
various arithmetic functions. 
A microprocessor is capable of integrating all functions needed to 
drive the recording device from encoders; see Figure 3. Encoder pulses 
cause interrupts which in turn cause incrementing or decrementing of 
"counters”. Physically, the counters are internal registers or memory 
locations whose contents are manipulated by the program of the micropro 
cessor. Shift of origin, scaling, and other simple arithmetic functions 
can be readily implemented. Means for communication with the recording 
device are available as a standard feature. 
Microprocessors can be used with minimum additional hardware to 
function as specialized system components, as was the case just explained. 
On the other hand, they may be expanded to become microcomputers. [14] 
The microprocessor is employed as the CPU of the computer and its per 
formance is boosted by additional memory, input/output channels, interrupt 
lines, etc. Figure 4 shows a recording system based on a microcomputer. 
The most reasonable place for it is probably at or in the recording de 
vice. The presence of a microcomputer permits great flexibility in re 
cording format, as well as some editing, data analysis, and further pro 
cessing, e.g., coordinate transformation. 
The trends that may be observed in the evolution represented by the 
examples described above, are quite typical. The trend is from specific 
to general, from hardwired to firmware and to software implementation, 
and in terms of performance from bare bones to considerable flexibility. 
Physically, there may be a trend that is not typical: the processing 
is moving toward the recorder. This is contrary to the general trend 
of distributed processing which tends to put processing power closer 
to the data source; encoders in this case. However, if the recording 
system is considered as a part of the entire photogrammetric process, it 
becomes quite clear that the general trend is valid also in this case.