2. THE SOFTWARE MODULE PSA 
The program package PSA (Progressive Sampling) has been developed 
by Mann (/8/) at the Institute of Photogrammetry, TU Vienna, to 
WILD's specifications and was first presented at the ISPRS-Meeting 
in Rio, 1984 (/9/). The latest release has further enhancements, 
which are described later. 
2.1 SOFT-, HARDWARE, AND HANDLING ASPECTS 
PSA is written in Fortran V and runs under the RDOS computing 
system. To control the WILD analytical restitution systems AC1, BCl 
or BC2 the routines of the User Software Interface Package (USIP) 
are used. PSA can be called as an independent data acquisition mo- 
dule in oriented models or directly from the Plotting Mode package 
(PMO) as a USER PROGRAM. PSA can be installed on the AVIOLYT system 
computer Nova 4/X or DG 20/30. In addition a plotting table TA2 or 
TA10 can be linked to the system so that online check plots can be 
made. 
The program is controlled by an easy to use menu technique, fully 
compatible with the AVIOLYT system and application software. The 
operator may exit at any stage. The data registered up to this point 
is saved and the operator can continue at any time from exactly the 
same point. Several function keys are available e.g. for changing 
the z/y components from handwheel to footdisc, for registering or 
skipping a point, leaving a search circle etc.. The measuring mark 
is driven to the precomputed position in x and y and approximately 
in z. The operator must now set the floating dot precisely on the 
ground and record the point. If it is not possible to set the mark 
another point within a radius specified from the program can be 
registered. The operator can always return back to the precomputed 
point and an acoustical signal sounds if the mark is outside the 
circle, but via key input he can store also a point outside that 
limit. Of course he can reject a point. 
A quadtree- database supports fast access to all stored points 
needed for the online terrain analysis in each densification step. 
The previously captured morphologic information is also stored in 
the database and always taken into consideration during the terrain 
analysis. These data are read from masspointfiles (MP-files) and 
may be captured on various ways e.g. with the PMO package. PSA 
produces an MP-file containing all sampled points locally stored 
in the database compatible with all other software like CIP or PMO. 
Thus further processing is possible. 
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