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DIGITAL PHOTOGRAMMETRIC STEREOCOMPILATION 
Digitizing a photogrammetric stereomodel is a more complex task than 
digitizing an existing map with well-defined features. Prior to merely 
following the features' boundaries and entering corresponding codes for 
attributes, the operator also has to identify and interpret the densi- 
tometrically defined half-tone objects seen in a model of the terrain 
surface. It is also self-evident that a photogrammetric stereomodel has 
to be properly joined to and merged in its surrounding neighbor models, 
and that it needs completion from other sources of information (see 
e.g. Kroell, 1981). 
The main purpose of photogrammetric stereocompilation is to supply to 
the cartographer an as complete, accurate and reliable (digital) manu 
script plot as possibly is achievable by an experienced human operator. 
This statement may be utilized to define a certain interface between 
photogrammetric and cartographic activities. Traditionally the photo 
grammetric operator has only been exposed to the use of a plotting 
table for data verification. Large table surface and high plotting 
accuracy, however, are tempting to not only produce a simple control 
plot but use it ultimately in the desired mapping scale with beautiful 
ly drawn point, line and area symbols, different colors, cross-hatch 
ing of polygons, straight lines and smoothed curves, etc. Actually, 
during photogrammetric stereocompilation the digitized data need only 
be made visible on a temporary, intermediate and most effective basis. 
It is not really necessary for the operator to see the whole control 
plot, nor are the digitized features to be shown in the final manner. 
It is completely sufficient to display digitized objects in a simple 
but clear and most obvious way. Emphasis lies on completeness and reli 
ability rather than on accuracy and cosmetics. High accuracy is 
achieved practically automatically by an experienced operator. Cosmet 
ics plays a role for the final cartographic map product, and belongs 
to there. 
The photogrammetric work station thus should contain an interactive 
graphics terminal. The scale of the plot may then be chosen at will and 
at any time, replotting of selected features or of the entire model is 
extremely fast, erasing of erroneous features is easily carried out. 
In general, the graphical representation on the screen reflects a true 
picture of the digitized data at all times. 
The stereocompilation process may be divided into three phases, viz. 
mensuration phase, model phase, and block phase. 
During the mensuration phase analog photogrammetric data are interpret 
ed and digitized according to linear feature-oriented criteria, and 
made visible in a graphical manner. A certain amount of this data must 
be constantly monitored and verified during the process of digitizat 
ion. Here, highest priority has to be given to the speed by which 
graphical objects, accumulated on the screen during the most recent 
period of some 15 minutes, can be corrected and improved ("visual real 
time control"). Using his or her short-term memory, the operator has 
to be able to easily and immediately edit visually recognizable incon 
sistencies between stereomodel and graphics picture prior to finally 
fixing the data on the screen and in the computer memory. The amount of 
data thus to be processed must be automatically and recursively adjust 
ed to the latest state of digitization. 
What matters in the model phase is the verification of completeness and 
consistency of the data as a whole accumulated within the current