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The following list explains the different projection types that can be
used with the camera. The most common types are the perspective and
orthographic projections. The CAMERA_TYPE should be the
first item in a camera statement. If none is specified,
the perspective camera is the default.
You should note that the vista buffer can only be used with the perspective and orthographic camera.
The perspective keyword
specifies the default perspective camera which simulates the classic pinhole
camera. The (horizontal) viewing angle is either determined by the ratio
between the length of the direction vector and the length of the
right vector or by the optional keyword angle,
which is the preferred way. The viewing angle has to be larger than 0 degrees
and smaller than 180 degrees. See the figure in "Placing the
Camera" for the geometry of the perspective camera.
The orthographic camera offers two modes of operation:
The pure orthographic projection. This projection uses parallel camera
rays to create an image of the scene. The area of view is determined by the
lengths of the right and up vectors.
One of these has to be specified, they are not taken from the default
camera. If omitted the second method of the camera is used.
If, in a perspective camera, you replace the perspective keyword by
orthographic and leave all other parameters the same, you'll get an
orthographic view with the same image area, i.e. the size of the image is
the same. The same can be achieved by adding the angle keyword to an
orthographic camera. A value for the angle is optional. So this second mode
is active if no up and right are within the camera statement, or when the
angle keyword is within the camera statement.
You should be aware though that the visible parts of the scene change when switching from perspective to orthographic view. As long as all objects of interest are near the look_at point they'll be still visible if the orthographic camera is used. Objects farther away may get out of view while nearer objects will stay in view.
If objects are too close to the camera location they may disappear.
Too close here means, behind the orthographic camera projection plane
(the plane that goes through the look_at point).
This is a spherical projection. The
viewing angle is specified by the angle keyword. An angle of
180 degrees creates the "standard" fisheye while an angle of 360
degrees creates a super-fisheye ("I-see-everything-view"). If you
use this projection you should get a circular image. If this isn't the
case, i.e. you get an elliptical image, you should read "Aspect
Ratio".
This projection is somewhat
similar to the fisheye but it projects the image onto a rectangle instead of
a circle. The viewing angle can be specified using the angle
keyword.
The omnimax projection is a 180 degrees
fisheye that has a reduced viewing angle in the vertical direction. In
reality this projection is used to make movies that can be viewed in the
dome-like Omnimax theaters. The image will look somewhat elliptical. The
angle keyword isn't used with this projection.
This projection is called
"cylindrical equirectangular projection". It overcomes the
degeneration problem of the perspective projection if the viewing angle
approaches 180 degrees. It uses a type of cylindrical projection to be able
to use viewing angles larger than 180 degrees with a tolerable
lateral-stretching distortion. The angle keyword is used to
determine the viewing angle.
Using this projection the scene is
projected onto a cylinder. There are four different types of cylindrical
projections depending on the orientation of the cylinder and the position of
the viewpoint. A float value in the range 1 to 4 must follow the
cylinder keyword. The viewing angle and the length of the
up or right vector determine the dimensions of the camera
and the visible image. The camera to use is specified by a number. The types
are:
Using this projection the scene is projected onto a sphere.
Syntax:
camera {
spherical
[angle HORIZONTAL [VERTICAL]]
[CAMERA_ITEMS...]
}
The first value after angle sets the horizontal viewing angle of the
camera. With the optional second value, the vertical viewing angle is set: both in degrees.
If the vertical angle is not specfied, it defaults to half the horizontal angle.
The spherical projection is similar to the fisheye projection, in that the scene is projected on a sphere. But unlike the fisheye camera, it uses rectangular coordinates instead of polar coordinates; in this it works the same way as spherical mapping (map_type 1).
This has a number of uses. Firstly, it allows an image rendered with the spherical camera to be mapped on a sphere without distortion (with the fisheye camera, you first have to convert the image from polar to rectangular coordinates in some image editor). Also, it allows effects such as "environment mapping", often used for simulating reflections in scanline renderers.
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