Graphics Reference
In-Depth Information
Figure
.
.
Query finding the water's edge
importance of interactivity, we select the sparse portion, Fig.
.
, which defines the
water's edge (Fig.
.
, right), and in fact more. By dropping the lower arrow, we see
thelakefillingupstartingfromtheedge(i.e.,shallowwaterfirst).herefore,thelower
values of B
reveal the water and the lowest “measure” shows the water's depth; not
bad for a few minutes of playing around.
But all this pertains to a single variable, when we are supposed to be demonstrat-
ing multivariate exploration. his is a valid point, but we did pick B
amongseveral
variables. Further, this is a useful “warm-up” for the more involved example that we
encounter next, since it has enabled us to present two of the queries. he astute ob-
server has probably already noticed the regularity, the vertical bands, between the
B
,B
andB
axes.hisiswheretheangle query, activated by the
A
button, comes
into play. As the name implies, it selects groups of lines within a user-specified angle
range.Adata subsetwhichcorrespondstoregions onthemapwithhighvegetation is
selectedbetweenthe B
andB
axesasshowninFig.
.
(let);theinter-axisdistance
is increased to better illustrate the vertical bands. Clicking the
A
button and placing
thecursoratthe middleofoneaxisopens anangle withits vertexinthemid-range of
the previous (let) axis. herange of this angle is controlled by the arrow movements
on the right axis. Actually, this “rule” (i.e., relation between some parameters) for
finding vegetation can be refined by tweaking a couple more parameters. his raises
the topic of rule-finding in general - classification - which is taken up in Sect.
.
.
he angle and pinch queries are motivated by the ℓline
point ℓ correspondence
in
-coords illustrated in Fig.
.
. To clarify the notation, m is the slope of the line
ℓ and b is the intercept (i.e., the line's intersection with the x
axis). As seen from its
x-coordinate,thepoint ℓ liesbetween theparallelaxeswhen m
<
,totherightofthe
X
axis for
and to the let of X
for m
<
m
<
. Lines with m
=
aremappedto
thedirection with slope b
d inthe xy-plane.Here d istheinter-axis distance and b is
theconstant (intercept)intheequation of ℓ.hisshows,thatdualities properlyreside
