# IBM Visualization Data Explorer User's Reference

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### Camera

Category

Rendering

Function

Constructs a camera for viewing an object.

Syntax

    camera = Camera(to, from, width, resolution, aspect, up,
                    perspective, angle, background);

Inputs

Name | Type | Default | Description
--- | --- | --- | ---
`to` | vector or object | [0 0 0] | look-to point
`from` | vector or object | [0 0 1] | position of camera
`width` | scalar or object | 100 | width of field of view (for orthographic projection)
`resolution` | integer | 640 | horizontal resolution of image (in pixels)
`aspect` | scalar | 0.75 | height/width
`up` | vector | [0 1 0] | up direction
`perspective` | flag | 0 | 0: orthographic projection 1: perspective projection
`angle` | scalar | 30.0 | view angle (in degrees) (for perspective projection)
`background` | vector or string | "black" | image background color

Outputs

Name | Type | Description
--- | --- | ---
`camera` | camera | resulting camera

Functional Details

This module differs from AutoCamera in that it specifies a "look-from" point for viewing an object (AutoCamera specifies a direction from which to view an object).

`to` | specifies a point in the scene that appears at the center of the image; the default is the origin of world space. This parameter can also be specified as an object, in which case the center of the object serves as the look-to point. Note: This parameter cannot have the same value as `from` (see below).
`from` | specifies the location of the camera; the default is [0 0 1]. This parameter can also be specified as an object, in which case its value is the center of the object's bounding box. Note: This parameter cannot have the same value as `to` (see above).
`width` | functions only for an orthographic projection (see `perspective` below). It specifies the width of the field of view, in world coordinates. If this parameter is specified as an object, the module uses a value that is slightly larger than the diagonal of the object's bounding box.
`resolution` | specifies the width of the image in pixels.
`aspect` | specifies the height-to-width ratio of the image.
`up` | specifies a vector that will be aligned with the vertical axis of the image.
`perspective` | specifies the method of projection used in rendering `object`: perspective (0) or orthographic (1).
Perspective projection | This method produces a realistic rendering of objects, but does not preserve their exact shape and measurements (e.g., parallel lines usually do not project as being parallel). The camera is positioned at the vertex of the viewing angle (see `angle` below). The two end-points of that angle are the left and right sides of the image area. Thus the wider the angle, the greater the amount of object space that can be fitted into the viewing area. Note: The `width` parameter has no effect on perspective projection.
Orthographic projection | This method produces a somewhat artificial view of an object (the distance between the front and back of an object appears small compared to the distance between the object and the camera), but it preserves exact scale measurements and parallel lines. The size of the object can be changed only by `width` (the default is a field of view slightly greater than the width of the object). The `angle` parameter has no effect on orthographic projection. In orthographic projection, only the direction of the `from`-`to` vector is important, not its magnitude. The object's distance does not affect its size in the image, which can be changed only with the `width` parameter. In perspective projection, the object's size can be changed only by changing `from` or `angle` (because `width` is ignored).
For more information on these projection methods, consult a text on computer graphics.
`angle` | specifies the viewing angle in degrees. The vertex of this angle is `to`.
`background` | specifies the color of the image background as either an RGB color or a color-name string. The string can be any of the defined color-name strings (see Color).

Example Visual Programs

    FlyThrough.net (uses the macro InterpolatePositionsMacro.net)
    FlyThrough2.net

See Also

AutoCamera, AutoColor, Direction, Render

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