The VIDEOMAP software in the host computer transfers digitized map 
data from the host computer to the VIDEOMAP input buffer. 
A microprocessor decodes the received data, converts graphics 
commands into the system code, and enters the data in the graphics 
memory. 
Any movement of the floating mark position is reported to the VIDEOMAP 
control unit directly by the stereoplotter. With the current floating 
mark position the microprocessor locates a window to the graphics 
memory content matched in size to the field of view and transfers the 
related data segment to the display memory. While this data selection 
and transfer is done as fast as possible (e.g. once per second with 
moderate memory load), the displayed video image will follow the 
photo carriage motion in fast real time (60 Hz). 
VIDEOMAP is connected to the host computer through a standard IEEE 488 
(HP-IB) interface. This interface is used by the host computer to 
transfer commands and parameters to VIDEOMAP and by VIDEOMAP to return 
requested data to the host computer. To support graphical output in the 
Zeiss VIDEOMAP system a transparent user-interface is given by means 
of the GRAPH V VIDEOMAP library /4/ which consists of a set of FORTRAN- 
subroutines. They generate VIDEOMAP commands which can be grouped as 
follows: 
Commands for generating the graphics display 
Commands for shifting the display segment 
Commands for entering and controlling text lines not to be shifted 
(e.g. messages, prompts) 
Commands for transferring data to the host computer 
(e.g. status, errors) 
Commands for controlling VIDEOMAP 
Each command consists of 2 letters followed, if applicable, by one or 
more parameters and the command delimiter. A detailed description of 
the VIDEOMAP interface gives the user the ability to develop 
additional programs to superimpose his own data in real time or at 
a random later time. 
3. WORKING WITH SUPERIMPOSITION 
Through digital mapping, photogrammetry has made a major advance: 
Graphical information is collected and coded in digital form, edited 
and plotted in separate steps. With digital mapping real time graphical 
output is theoretically not required, but graphical logging is 
generally considered more efficient compared to "blind" digitization. 
Dynamic superimposition is obviously setting a trend for direct 
acquisition of clean data. The operator may "move" through his model 
and retain the digital/analog relationship. Three major tasks can be 
classified in which optical superimposition plays an important role: 
Data acquisition, data revision and project planning. 
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