4.3. To Tune a View

To tune a view, choose Edit->Settings. The View Settings Dialog Box opens.

This dialog box can be used to change the following parameters:

Background color

The background color is selected by clicking on the button and picking a color in the dialog box that pops.

Field of view

The field of view is the angle which sides join the point from which the model is viewed to the nearest sides of the view. So if the view has a larger horizontal size than its vertical size the sides taken into account are the horizontal ones, otherwise, the vertical sides are used. Acceptable values for the field of view are betwwen 0 and 45°. When a 0° field of view is used the projecton is orthogonal. With a 1° field of view, the perspective effect will be hardly perceptible and with a 45° angle, the model will appear sowhat distorted. The default field of view is 10° (unless you changed it) and gives a sensible perspective.

The distance between the viewpoint and the model is calculated to be the shortest so that the whole model remains visible whatever its orientation is. The only solution to see the model from a longer distance consist, in the present version, in defining a greater model size (see Section 3.4) and defining cleavages to remove extra atoms (see Section 3.5) while selecting the option of constant model size.

Spatial model orientation

The model may be oriented with the mouse, clicking on the left button inside the view, dragging until a convenient orientation is obtained, and releasing the button. It also is possible to use this dialog box to choose an orientation by modifying the three Euler's angles ψ, θ, and φ.

When the three angles are null, `c` axis is vertical, with positive values up, `b` axis is in the view plane with positive values towards the right, and `a` axis points in the direction of the viewer. To bring the model to the position defined by Euler's angles, the operations are, in order:

• A rotation by angle φ around the vertical axis oriented upwards. Possible values for φ are in the range - 180° to 180°.

• A rotation by angle θ around the axis perpendicular to the view and pointing towards the viewer. Possible values for θ are from 0° to 180°.

• A rotation by angle ψ around the vertical axis oriented upwards. Possible values for ψ are in the range - 180° to 180°.