|
The SEDRIS Data Representation Model
APPENDIX A - Classes Camera Point |
|---|
An instance of this DRM class specifies an eye point to view from, specifying a location, an orientation, and either an orthographic or perspective viewing volume.
A viewing volume is defined, oriented along the axis defined to start at the camera <Location 3D> and oriented as specified by the components of the <Camera Point>. This orientation defines the coordinate space of the camera, where the camera is at (0, 0, 0) and is oriented to look down the +Y axis (assuming the XY plane defines the horizontal plane and the right-hand rule applies).
The viewing volume of a given <Camera Point> instance is defined based on two planes specified by two parallel rectangles in space, the near clipping plane and the far clipping plane. The near clipping plane is the plane perpendicular to the camera axis and located camera_near metres from the <Location> of the <Camera Point>. The far clipping plane is parallel to the near clipping plane, but is located camera_far metres from the <Location> of the <Camera Point>.
If projection = SE_CAM_PROJ_TYP_ORTHOGRAPHIC, then the viewing volume is the parallelepiped volume between the two clipping planes, bounded by the rectangle specified by (left, bottom) as its lower left corner and (right, top) as its upper right corner.
If the camera defines a perspective view point, then the viewing volume is a frustum that can be described by in one of two ways. The perspective viewing volume can be defined as the volume starting at the near clipping plane rectangle and expanding to the far clipping plane. Alternatively, the perspective viewing volume can be described by a field-of-view angle, an aspect ratio that is the width of the frustum divided by its height, and the distance to the near and far clipping planes.
A perspective viewing point defined at the beginning of a runway, oriented to look down the runway.
An orthographic viewing point defined high above the transmittal, in the centre of the transmittal, to give a "God's eye view" of the entire transmittal.
Typically, <Camera Point> instances are used for pre-set views into a transmittal. They can also be used for eye point attachments for own-ship <Model> instances.
The semantic meaning of this relationship is that the given <Image> instance represents a picture taken from the location of the given <Camera Point> instance with the given aspect ratio, camera projection, and camera axes as specified by the <Reference Vector> instances. The <Image> instance should be of the data described under the <Aggregate Geometry> instance of which the given <Camera Point> instance is a component.
The projection_field specifies the type of perspective projection in use by the given <Camera Point> instance.
The camera_near field specifies the distance from camera position to near clipping plane, in metres.
The camera_far field specifies the distance from camera position to far clipping plane, in metres.
If the value of the use_left_right_bottom_top field is SE_TRUE, use the parameters from the left, right, bottom, and top fields. These fields are always used for orthographic viewing, but perspective viewing can either use these fields or the field-of-view and aspect ratio fields.
The left field specifies the X coordinate of the lower left corner of the rectangle in the near clipping plane.
The bottom field specifies the Y coordinate of the lower left corner of the rectangle in the near clipping plane.
The top field specifies the Y coordinate of the upper right corner of the rectangle in the near clipping plane.
The right field specifies the X coordinate of the upper right corner of the rectangle in the near clipping plane.
The horizontal_field_of_view field specifies the angle, in radians, of the horizontal field of view. This value is used for perspective viewing if the use_left_right_bottom_top flag is SE_FALSE, assuming a on-axis symmetric viewing volume. Off axis viewing volumes are not supported.
The aspect_ratio field specifies the width of the frustum divided by its height. This value is used for perspective viewing if the use_left_right_bottom_top flag is SE_FALSE.
|