

line smoothing algorithms Cartographers produce manuscript lines
which have a smooth 'flowing' appearance. In comparison, digital lines
tend to be angular and nonaesthetically pleasing (particularly at large
scales)  this is due mostly to the constraints of the digitising grid.
Unlike simplification, which endeavours to reduce detail, smoothing techniques
shift the position of points making up a line, in order to remove small
perturbations and capture only the most significant trends of the line.
Hence, smoothing is used to improve the appearance of digitised lines
or, more simply, for cosmetic modification. Figure 1 shows a line before
and after it has been smoothed. 

Figure 1. Line Smoothing (Source: McMaster & Shea 1992)


As Figure 1 illustrates, the aesthetic
appearance of a line can be greatly improved by applying one of the many
smoothing operators. There are various ways that smoothing algorithms
can be classified, see Table 1 below for one such classification. 

Table 1. Characteristics of smoothing algorithms (Source: Lewis 1990 in McMaster & Shea 1992)


There are several line smoothing algorithms,
including McMaster's Distance Weighting Algorithm,
Boyle's ForwardLooking Smoothing Algorithm and Chaiken's Smoothing
Algorithm. The algorithm at the focus of the line smoothing section of the
module, though, is known as McMaster's Slide Averaging
Algorithm.There is a link below (on the right) to one interactive
lesson which will help you to visualise how McMaster's
Slide Averaging Algorithm
is applied when smoothing a line. If you wish to read/revise any theory
at this stage, follow the links on the left. 

Background Theory
Links:

McMaster's Slide
Averaging Algorithm Interactive Lesson:


Click here to download all theory presented in this module  
references  
