3.1 Superimposition and data acquisition 
Cost effective data capture is crucial to digital mapping. Super- 
imposition of the current measurements helps to create immediately 
clean digital data and thus leading to increased overall throughput 
by largely reducing editing steps. 
First of all superimposition enables geometric àccuracy checking of 
direct measured points and lines. Beyond that it is particularly 
valuable while measuring with adjustment algorithms. Spline 
computations may proved with regard to their representation of the 
real curve. The PLANIMAP software furthermore supports the measurement 
of buildings by computation of invisible corners by line intersections, 
recognition of right angles within a given tolerance, adjustment of 
errored right angles or aligning the buildings to a reference direction. 
The computation result can be compared directly with the original object. 
Line adjustment is another application where superimposition serves as 
a valuable aid. A polygon to be captured may have invisible nodes or 
nodes which are not clear detectable. Measuring desired points of the 
polygon the algorithm computes an adjusted polygon. The superimposed 
solution gives the operator the ability to compare the measured 
polygon with the adjusted polygon for acceptance or non-acceptance. 
  
Much conventional editing work will be saved if accuracy and 
compatibility of nearby features can be guaranteed during data 
collection. Narrow lines running side by side can be measured without 
crossing each other. Symbol placement, text placement and point number 
placement can be finalized. 
Direct superimposition permits semantic accuracy checking to realize 
object identification errors or symbol assignment errors. 
  
Double measurements of sides of buildings in closely build-up areas 
or property boundaries in highly dismembered regions can be avoided 
as well as double measurements of lines already calculated by the 
parallel-line function. On the other hand incompleteness is avoidable 
as omitted features are eye-catching. 
  
Probably the most valuable advantage to obtain clean data is the 
linkage with features measured right before. Superimposition relates 
the position of the measuring mark to that of a previous digitized 
point or line. An interactive function such as 'snapping" searches 
for the corresponding point and delivers exact coordinates out of the 
data base. Whenever lines do have to meet, for instance as it is to 
be found always while measuring side-buildings, clean connections are 
averting editing steps such as “clipping” or “hanging on". A polygon 
or curvilinear feature can be closed simply. Lines can be continued in 
an accurate way especially at model edges. VIDEOMAP gives the ability 
to pursue lines by superimposing a successive model with the data of 
the previous model in order to show the interrupted lines for an 
accurate continuation after a "snap" to it. With that the edge matching 
problem is solved! A special edge matching software to remove 
discrepancies between two independent digitized adjacent models 
is unnecessary. 
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