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6  Visualisation interface: an Overview

6.1  Handover

This section consists in a small tutorial on how to use Explorer3D in the context of a PCA.

When starting Explorer3D , the main control window opens (cf. fig. 1).

Figure 1: Explorer3D main control window (at launch time)
Figure 2: PCA commands

Let us first load the data file. In the menu bar, let use choose “Files / Load local file (new project)”, and pick the iris.csv file. The main window aspect changes, so that it now offers the functionnalities that are relevant to a feature file (also called the “ND[imensions] → 3D[imensions]” perspective (see fig. 2).

In order to compute a classical PCA, we first check, in the “Pre-treatments” sub-window, that “Center variables” is checked, and that “Reduced variables” is selected in the “Reduction method” list. Let us then click on “Compute” in the “Projection Method” sub-window. The 3D view then opens and displays objects using their default shape and colour, that is blue spheres on a dark background (fig. 3).

Figure 3: Default 3D view

Let us now display an additional visual information, by the mean of object colouring according to their class (each sphere correspond to a given kind of iris, and each kind of iris belongs to one of three varieties). The class of a given iris (i.e. its variety) is stored in an additional attribute, load together with the features, and named “classe”. Let us display the sub-window “Additional attributes” by clicking on the upper-rigth arrows of this sub-window, and let us choose “classe” in the “Groups” list (which is the only attribute available, let-us ignore “multigroups” for the moment). spheres are then coloured and a legend window pops up (fig. 4).

Figure 4: 3D View with colour and legend

We can notice the presence of check boxes in the legend window. The “class” check boxes allow to display or hide the objects that belong to a given class. The “Ellipsoid” checkboxes allow to display an ellipsoid around the corresponding group of objects (i.e. the objects of a given class), that reflects their spreading in space (fig. 5) (Basically, this ellipsoid is centered on the center of gravity of the group, and its diameters correspond to the variance of the group along its three mains axes, based on the hypothesis of a multinormal distribution). Figure 5 illustrate a visualisation of objects and the classes ellipsoids.

One must notice that the top-line check boxes (blue background) are shortcuts to check or uncheck the whole column.

Figure 5: Groups Ellipsoids

It is also possible to view the convex envelop of a group. This is done by checking boxes in the “Convex Envelop” column. Figure 6 illustrates a 3D view where objects have been hiden and only convex envelops are displayed.

Figure 6: Convex envelops

Last, we can interact with the 3D view by using the three mouse buttons (left: rotation; center: zoom; right: translation).

6.2  Control window menus

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