Figure 35: Polar Filtering Fisheye View of Attributed Syntax Tree
Filtering fisheyes [SaBr94, Sa96b]
show many details at the focus point, but
they filter graphical objects that are far from the focus point.
This improves the visibility of the main structure, which would
probably go lumpy with all the shrunk, unimportant details
far from the focus point.
Thus, objects are filtered according to their visual worth.
The visual worth depends on the distance to the focus point
and on an a priori importance (api) of the
nodes and edges of a graph, which is given in the graph specification.
For instance, in an attributed syntax tree, the main structure is the tree,
thus it has an larger api than the attributes.
The user can select the threshold level of detail (lod) to
influence the amount of visible objects.
An object is visible if 
, where x is the
distance to the focus point and h is the function calculating the
visual worth.
Properties of h:
if 
.
The function h is monotonic decreasing wrt. distances.
Objects far from the focus point are less interesting,
since the focus point is the point of interest.
if 
.
The function h is monotonic increasing wrt. api.
Objects with small api are less important and can
be preferred for filtering.
