 Home Engineering Tactile Display for Virtual 3D Shape Rendering

# Phase 2: Managing of the Control Points

Now that the trajectory to render has been defined, it is possible to start the second Phase, which is in charge of managing the position of control points. To obtain a flexible system we designed three different modalities for managing the control points, thus allowing the user to select the more appropriate to his/her needs.

Therefore, the Phase 2 can be performed selecting one of the 3 different modalities:

• • Modality with constant distance between control points;
• • Modality with central point definition and variable distance between control points;
• • Modality with interval definition and variable distance between control points.

## Modality with Constant Distance Between Control Points

The modality with constant distance between control points allows the user to select the nominal distance between the control points. The user can choose the position of the central point, which is the fixed one of the device. After that, the software calculates the position of the other points so that the length of the curve between two points is equal to the nominal distance. Therefore, in this modality, the control sectors do not slide on the strip. Figure6.12 shows a conceptual example of the control points management for a generic trajectory in the modality with constant distance between control points.

Once that the positions of the points are defined, it is possible to calculate the normal vectors to the surface in the obtained points. By means of these vectors is possible to obtain the values of the angles needed to define the torsion and the tangency degrees of freedom. As shown in Fig. 6.13, the coordinates of the points and the values of the calculated angles are the output of Phase 2.

This modality is faster then the other two modalities, because it does not require complex function analysis and it can be used, whenever the user desires, in order to analyse small portions of the surface with high accuracy.

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