Figure 3.-IDPF standard interface. 
IDPF COMMUNICATION PROTOCOL 
Communication between the IDPF controller computer and the VPSV is 
handled within a shared common area in the controller's memory. This 
shared memory is organized into an input and output region. The 
input region is used to transfer data from VPSV to IDPF. This data 
represents the current status of various components of the VPSV. 
The VPSV is required to regenerate this region at real-time rates 
(50-60 cycles per second). The parameters in this region are as 
follows: 
o Current planimetric position of the two photographic 
stages 
o Accumulated counts for each valuator since last reading 
cycle 
o Bit pattern for control panel 
The output region is generated by IDPF at an undefined rate. 
However, the VPSV is required to service requests indicated by the 
contents of the output region at real-time rates. The parameters in 
the output region represent requested actions by IDPF for the VPSV to 
execute. The parameters in this region are as follows: 
o Target planimetric position for two photographic stages 
o Required image rotation for each stage 
o Required magnification for each stage 
o Size of measuring mark on each stage 
o Illumination of each stage 
o Illumination of measuring mark for each stage 
o Setting indicators for control panel (such as lights) 
o Audible signal tone and duration 
The input and output areas of the shared common region represent the 
total information required to regulate IDPF's communication with the 
VPSV. The capabilities of the VPSV are broader than any 
photogrammetric stereoviewer currently in existence. A stereoviewer 
is in compliance with IDPF standards if it satisfies the following 
two conditions: 
1. The stereoviewer can transcribe its status to the read 
region of shared memory in the control computer. It is 
required to provide information for only the 
stereoviewer's hardware facilities which are computer 
controlled. 
2. The stereoviewer can respond to requests from IDPF as 
indicated by the output region in shared memory of the 
control computer. The stereoviewer should respond only to 
those requests which can be executed on its hardware under 
computer control.