O
object
An integrated, organized unit of data stored either in a project file. These include raster, vector, database, and text object types.
opaque color
When a new color feature completely masks out an earlier feature in an image, the new feature is composed of opaque color. For example, a polygon can be overlaid or drawn in opaque color upon an image so as to completely obliterate the original features in that portion of the image.
open reel tape
Medical images and satellite images from mainframe and minicomputers are commonly distributed on 12-inch reels of magnetic tape in standard format. A microcomputer with a open reel tape drive can copy image files directly from tape.
operand
A parameter that designates a raster object's identification and location in a raster algebra expression.
operator
The function in a raster algebra expression that describes action upon a raster object or the process by which raster objects, or operands, are to be combined.
optical disk
A high-capacity medium for computer file storage that uses removable optical disk cartridges that function like removable hard disks. Each side of a two-sided optical disk typically holds from 300 to 500 megabytes of data. Some optical disks (WORM disks) record data permanently: once data has been written on a WORM disk it cannot be erased or changed. More recently, erasable optical disks have been developed. (See also: erasable optical disk, WORM drive.)
optimization table
The translation table that determines the color assignment in the color map that results from the optimization process. Optimization tables are used to assign display colors for multiple raster display in 8-bit contexts.
option
An item on a menu. Also called a selection.
option button
A type of button that opens an option menu. When a new selection is chosen from the option menu, the new selection is displayed as the button label.
ORACLE
A relational database Management System to which ARC/INFO has access through the DATABASE INTEGRATOR
origin (X-Y digitizer)
The point on an X-Y digitizer's active area which has the coordinates (0,0). The origin is typically located in the lower left corner of the active area, but can be relocated in many digitizer models.
orthoimage
An airphoto or satellite image that has been processed to remove perspective distortions and so to have the properties of an orthographic projection. Distortions of tilt and relief are removed so that all features in an orthoimage are in their true orthographic positions.
ortho photo
An airphoto that has been scanned, rectified, and reconstructed so as to represent its features in a map projection or at least in a flat rectangular form without the usual distortions of geometry and perspective. Usually orthophotos are prepared from very high resolution stereo pairs.
ortho video
Airvideo images always include some geometric distortion from the camera, lens, movement and perspective. Orthovideo images have been geometrically corrected with control points from a corresponding vector object. The control points are used to rubbersheet or warp the airvideo frame to yield a new raster with more map-like geometric properties.
outline font
A font in which each character is described by a set of lines or polygons rather than by individual pixels. Thus, outline fonts can be rescaled to any size and displayed at any resolution with no degradation of appearance. (See also: bitmapped font.)
outline highlight or location box
Shows which menu selection or button in a window is the object of keyboard or mouse focus.
overlay
(vector or CAD) A transparent layer placed on an underlying image. The overlay is where symbols, annotations, or image traces can be created or displayed without changing the underlying image.