International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B6. Istanbul 2004 
  
       
  
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Figure 
6.1 Procedure for building enlargement 
In going from one step to another, some areal entities need to be 
enlarged in order to be distinguished clearly and identified. The 
enlargement is performed in two different ways depending on 
whether it necessary to increase their surface or their 
thickness. 
This kind of operation is performed for buildings by the 
Enlarge Buildings procedure within the Generalize Buildings 
function. On the other hand, it is not implemented for soil 
occupation areas (vegetation and so on) which are simply 
eliminated if they have less than a given surface area. 
Is 
The purpose of this procedure is to increase the surface area of 
areal entities and their thickness up to a predetermined 
minimum value. The enlargement procedure makes use of two 
different algorithms, one to enlarge the surface area and the 
other to increase thickness. 
The choice of one or the other essentially depends on the 
distance of initial values from the minimum values. In the most 
general case both algorithms are applied to the entity, in an 
attempt to satisfy the two constraints together, but at the same 
time attempting to limit changes in shape. As a parameter for 
characterizing the shape of the object, compactness is chosen 
and this must not vary beyond a given percentage. 
6.1.1 Increase in surface area: The minimum enlargement 
value is normally assumed to be equal to the threshold of 
interpretability of the entity considered. For buildings, this 
value is usually established at between 300 and 500 square 
MOM 
metres at the scale of 1:5669N 
75 
The algorithm operates quite simply, scaling the entities by a 
scale factor defined by the ratio between their initial surface and 
the desired surface with respect to their barycentre. 
6.1.2 Increase in thickness: The aim of this algorithm is to 
increase the thickness of the areal entity up to a minimum value. 
Since entities are of variable thickness, theoretically a localized 
enlargement should be made, with thickness increased only 
when necessary. 
À procedure of this kind leads to a loss of shape of the entity 
and is already implemented partly during simplification of 
outlines. In the case of contour simplification, a minimum value 
equal to the readability limit that can be accepted for small 
variations in the entity's shape was used. For this reason, the 
algorithm uses the mean thickness of the object which is 
defined on the basis of the parameters of only area and 
perimeter instead of local thickness. These values are 
immediately accessible in the planning stage and allow an 
immediate estimate of mean thickness. 
After calculating the value of mean thickness and defining the 
value of minimum thickness, the algorithm operates in a simple 
way by creating a buffer equal to half the difference between 
minimum and mean thickness around the entity. 
Figure 4. 
6.2 Procedure for thinning out areas 
The need to reduce the number of areas becomes 
time their density hinders their representation 
scale. 
The thinning out of areas is performed in two 
depending on whether or not it is based 
considerations or on topology and proximity. 
The former operation is implemented over all areal entities, 
whether or not they represent built-up areas or soil occupation 
areas; the latter operation is performed only for built-up areas. 
manifest every 
at the derived 
different ways 
on geometric 
6.2.2 Geometric thinning out: In this case thinning out of 
areas 1s performed on the basis of their surface and the 
parameter that identifies the elements to be eliminated is 
defined by the minimum area value. As in the case of linear 
entities, this algorithm does not take into consideration the: 
context in which the entity is present but only its geometric 
characteristics. Choice of the minimum area value is not 
dictated by the readability threshold of areal elements, but by 
considerations of a semantic nature. Buildings below the 
visibility threshold are enlarged and non-contextual elimination 
is allowed only when they are not considered significant for the 
representation. to. be obtained. It is clear that very small 
buildings which may be significant at a large scale are scarcely 
significant at a medium scale and enlarging them would lead to 
an erroneous estimate of their characteristics. 
This type of thinning out is performed for buildings at the same 
time as their simplification in shape by the resident Centerline 
function, while for soil occupation areas it is implemented by a 
procedure within the Generalize Area function activated inside 
the ArcMap environment by means of a pushbutton. 
6.2.3 Thinning out by topography and proximity: 
Following enlargement operations, some entities are