5.89. Viewpoints (element)

5.89.1. Attributes

5.89.2. Description

This element is a child element of a user elements. Its string attribute default_viewpoint defines a viewpoint that is chosen as its default viewpoint for this user. Its content defines a list of shots, each of them is made of a viewpoint number, and two dates that define the beginning and the end of the shot. They are used for predefined animations: they define a list of viewpoints that will be active in turn for the user. They correspond to camera cuts in a traditional movie.

The integer value of the default_viewpoint attribute defines the index of the viewpoint that is chosen as default viewpoint. The viewpoints are indexed in the order in which they are encountered in the scene description, the first one is viewpoint number 1. In addition to these explicitly defined viewpoints, there is a base viewpoint numbered 0 that is located at the origin. In case of alternate stereo viewing through two user viewpoints, default_viewpoint is the index of the default right eye viewpoint while default_viewpoint_stereo_left is the index of the default left eye viewpoint.

If the index attribute is not provided and if the xlink:href attribute is provided, it is used to refer to the default viewpoint by its URI reference.

If no default viewpoint is defined and if the scene contains at least one viewpoint, the default viewpoint is the first viewpoint. If no default viewpoint is defined and if the scene does not contain any viewpoint, the default viewpoint is the base viewpoint.

The integer value of the shots attribute defines the number of shots for the user in which this element is embedded. If no shot is defined (value 0), the viewpoint is the default viewpoint and there is a single shot for the whole scene (this configuration is appropriate for interactive environments). If n shots are defined, the elementary shots must contain n triples of numbers made of:

1. an integer viewpoint number between 0 (the base viewpoint at the origin) and c the number of viewpoints,

2. a float begin date that defines the time at which the shot will begin,

3. a float end date that defines the time at which the shot will terminate.

After the last shot end date, the scene continues with the last viewpoint. The termination of the scene only depends on the value of the last_frame_number of the element trace.

In case of alternate stereo viewing through two user viewpoints, each shot is defined by two indices (the left and right eye viewpoint) and two dates, a beginning and an end date.

5.89.3. Expected content

This element must contain as many triples as the integer value of the shots attribute. Each triple is made of an integer (a viewpoint number) and two floats (the begin and end times of the shot).

5.89.4. Example

The example below defines a scene made of three shots, the first one uses the viewpoint #1 from time 0 to time 15.0, the second one uses the base viewpoint from time 15.0 to time 25.0, and the last shot uses the viewpoint #1 from time 25.0 to time 30.0.

<viewpoints default_viewpoint="1" shots="3">
     1   0  15
     0   15 25
     1   25 30
</viewpoints>

The example below defines a stereo scene made of three shots:

<viewpoints default_viewpoint="1"
            default_viewpoint_stereo_left="2" shots="3" >
    1 2  20 40
    5 6  40 55
    1 2  55 83.48
</viewpoints>