Geography Reference
In-Depth Information
Direct manipulation techniques allow the user to point to and
pick
interesting elements
to select, delete or adapt them. Various researchers have used different names to express the
same technique, including
highlighting
(Robinson, 2006),
brushing
(Carr
et al
., 1986; Becker
and Cleveland, 1987) and
painting multiple views
(Buja
et al.
, 1991). However, the techniques
remain the same: a user visually selects one or more elements, the elements are stored or
processed, and the selected elements are displayed to the user through highlighting.
Commonly the selection operation is coordinated to all windows to allow the user to see
how elements in one projection are displayed in others. Linked brushing is important, as the
user can brush in one view in one projection and see the results of that operation in other
dimensions in other views. Linked brushing can also be used to discover outliers between
multiform views (Lawrence
et al
., 2006).
There are different tools to directly select the required elements. Commonly a freehand
lasso is used to delimit the elements (Wills, 1996), but the brush can be a point, line or area.
For example, Stuetzle (1987) demonstrates point selection and Becker, Cleveland and Weil
(1988) describe a line-brush, while there are many examples of bounding boxes (Becker,
Cleveland and Wilks, 1987; Buja
et al
., 1991; Swayne
et al
., 2003; Ward, 1994, Piringer
et al
.,
2004; Weaverm, 2006).
Often
highlight
is the only operation that developers implement. However, even 20
years ago, Becker and Cleveland (1987) specified four brush operations: highlight, shadow
highlight, delete and label. The
highlight
operation changes the appearance of the selection
list in all windows;
shadow highlight
changes the appearance of the selected elements in
the view and removes them from all other linked views;
delete
removes the elements from
the view; while
label
displays additional information about the selected elements, such as
a text label. More recently, researchers have extended these ideas, e.g.
multiple brushes
or
compound brushing
. Multiple brushes allow users to control many brushes, with each new
brush in a different colour. Compound brushing combines the results from multiple brush
operations. Chen (2004) describes a flexible compound brushing system that permits
selections to be combined using various logical operations (e.g. AND, OR, XOR), the
operations being controlled through a graph layout, while Wright and Roberts (2005)
present a direct methodology named
click and brush
.
Finally, the selected elements need to be visually
highlighted
. Commonly this is through a
colour change, but other methods include linked lines, depth of field, transparency, contour
lines or shadows surrounding the elements (Robinson, 2006).
3.4.4 Navigation
Navigation and
viewpoint manipulation
can come in various forms. With three-dimensional
geovirtual environments the user can walk, fly, clip to remove information, and change the
projection transformation (such as from parallel projection to perspective projection). How-
ever, users often get lost in their navigation, for instance map users lose orientation infor-
mation (Gahegan, 1999). Thus, techniques that control and constrain the user's navigation
are often useful (Buchholz, Bohnet and Dollner, 2005). Linked master-slave navigation can
also allow the user to navigate efficiently in dual view systems (Plumlee and Ware, 2003), see
Section 3.3.1. In two-dimensional maps the user can zoom or pan (Harrower and Sheesley,
2005) and scroll, and often the zooming operations are associated with a semantic change
(Cecconi and Galanda, 2002). Often multiple views are linked together such that one is the
focus and the other provides detail (Convertino
et al
., 2003).
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