International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B6. Istanbul 2004 
  
  
5.1 Functions resident in the software platform 
The ArcGIS software platform used in this work contains some 
functions dedicated to generalization. The main functions used 
in the course of this work are the following: 
- the function Create Centerline 
- the function Simplify Buildings 
- the function Simplify Lines 
These three functions accessible in the ArcToolBox 
program. The Create Centerline function was applied to the 
covers containing the road and fluvial networks on the entities 
that went into the definition of the single road shoulder or river 
bank. 
The Simplify Buildings function simplifies buildings and other 
prevalently squared-off entities, thus reducing the details of 
their perimeters and maintaining the essential features of their 
shape and original dimensions. Buildings are, in general, 
orthogonal areas and this kind of simplification maintains and 
increases their orthogonal nature. 
This function was applied, in the course of our experiment, to 
covers containing the building and to those containing the other 
buildings represented with areal entities. 
The Simplify: Lines function was not used in the generalization 
process. It was in fact possible to use the Generalize method, 
which implemented the Douglas-Peucker algoritm, for the 
Polyline class. 
We then implemented a procedure dedicated to simplification of 
linear elements which exploited this possibility within the 
development environment. 
are 
5.2 Procedures implemented for the first time 
The procedures that were implemented ex novo can be classified 
on the basis of the kind of operation they perform: 
Procedures for restoration of congruousness and continuity 
e Procedure for the merging of lines 
e Procedure for joining broken lines 
Procedures for logical thinning out 
e Procedure for thinning out punctual objects 
e Procedure for thinning out lines 
Procedure for thinning out areas 
Procedures for simplification of shapes 
e Procedure for line simplification 
Procedure for the simplification of areas 
Procedures for enlarging areas 
e Procedure for enlarging buildings 
e Procedure for widening buildings 
Procedures for area aggregation 
e Procedure for aggregation of buildings 
e Procedure for aggregation of areas of soil occupation 
General procedures 
e Procedure for generalization of buildings 
Procedures for transformation of the original and changes in 
attributes 
Procedure for the collapse from areal to punctual entity 
Procedure for change of the cartographic code of the entities 
For brevity's sake, attention will be focused on the procedure 
for generalization of buildings. 
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6. PROCEDURE FOR GENERALIZATION OF 
BUILDINGS 
The aim of the procedure is to increase the dimensions of the 
entity up to the predetermined minimum values while 
maintaining the original shape and at the same time avoiding 
superimpositions and ensuring respect for the relative minimum 
distances through elimination and aggregation. 
For generalization of buildings the procedures of enlargement, 
thinning out and aggregation are used jointly and are 
implemented within the Generalize buildings function. which 
can be implemented in the ArcMap environment. 
The first procedure applied is that of enlargement, which 
increases the dimensions of the entity up to the required 
minimum. Enlargement is applied progressively following a 
number of steps determined beforehand. At each step any 
superimposition conflicts that may arise are indicated. Once the 
conflict has been highlighted, a special procedure chooses the 
next operation to be applied (thinning out or aggregation) on the 
basis of a cost function employing the relationship between the 
dimensions of the two entities as a variable. At the end of the 
enlargement procedure any proximity conflicts are pointed out 
and also in this case they are addressed gradually by varying the 
minimum distance up to the final value. Both the aggregation 
and thinning out procedures lead to a resolution of conflicts and 
respect for the no superimposition (topological) and separation 
distance (proximity) constraints. Depending on the typology of 
the two objects and the density of the conflicting buildings, one 
or the other of the two procedures is found to be the more 
suitable. 
One way of making the choice is to compare the dimensions of 
the two buildings. If they are more or less the same size the 
ideal solution is that of aggregation. But if one is clearly larger 
than the other the best solution is to eliminate the smaller one. 
Another method for optimizing the choice is to evaluate the 
building's density. Indeed, while aggregation does not make 
room for the other entities, thinning out produces too much 
open space. An optimal balance between aggregation and 
elimination leads to a result that is more harmonious and 
respondent to the reality it is representative of. The subdivision 
of the process into a defined number of steps allows simulation 
of a continuous enlargement, with the highlighting of conflicts 
as soon as they occur. This ensures that conflicts occur 
prevalently between a limited number of entities and can be 
resolved easily two by two. Application of enlargement in a 
single step would lead to a large number of conflicts, thus 
complicating the choice of the entities to eliminate or aggregate. 
In the same way, in the case of proximity conflicts, this way of 
proceeding allows dealing first with the entities closest together 
and then all the others. The more the steps in the procedure the 
better the final result will be; however, this creates an excessive 
process cost both in terms of time and memory. It has been 
found that three to five steps are sufficient to produce a good 
result. With more than five steps the increase in process cost 
does not produce a corresponding improvement in the results.