Interactive Scale-dependent multidimensional Point Data Selection using enhanced Polarization Transformation - Advances in Cartography and GIScience - page 399

Deutsche Flugsicherung GmbH and the EUROCONTROL Information
Centre. The dataset contains points representing airplane positions over the
area of Germany. We used the positions of 405 airplanes from the

15.05.2009 at 9:26:00 o'clock. We applied this data set to our enhanced
PT-approach.

Figure 4 and Figure 5 show screenshots of our interactive selection tool for
multidimensional point data using the enhanced PT approach. Fig. 4 shows
an example for 2D points and Fig. 3 shows an example for 3D points. The
user can load any point data set, 2D-points (x,y), 2½D-points (x,y,t), 3D-
points (x,y,z) or 3½D-points (x,y,z,t). In the plot of the original points (top
left) the Polarization-centre ( P c ) is drawn with a blue colored circle. After
defining the original scale (scale1) and either the reduced scale (scale2) or
the number of points which have to be eliminated (in number or percent-
age), the polarization space and the segmented spectrum line will be calcu-
lated and displayed. Depending on the original data set (xy- or xyz-
coordinates) either 2D plots ( Figure 4 ) or 3D ( Figure 5 ) plots are dis-
played. Through a time slider the user can change the coordinates for the
particular time and will get the regarding selection displays in real time. In
the polarization space all points are drawn in black. If points are kept as
local maxima they are drawn with cyan colored circles, in case of local
minima they are drawn with green colored circles. Points which have to be
eliminated are drawn with a red colored circle. For 3D- or 3½D-point data
three spectrum-lines are plotted, xy-diagram, xz-diagram and yz-diagram
( Figure 6 ) . Thereby the potential to be eliminated points are drawn in pur-
ple and in red color. The red points occur in all three spectrum-lines and
will be finally eliminated.

The results are drawn in the top middle plot which shows the kept points in
black color and in the top right plot the deleted points are shown in red
color. The number of the kept and deleted points is displayed in each case
in the sub-plot title.

In our example for 2D point selection, shown in Fig. 4 , an initial scale of
1:1000 and a reduced scale of 1:2000 were set. All detailed results (deleted
points in each perspective, finally deleted points, etc.) after applying the
enhanced PT are listed in Table 4 .