Glossary

Popular terms used throughout this website

 


CHANGE DETECTION

A process of showing changes between two images of the same area, collected at different times. Typically, pixel-by-pixel comparisons are made and output is generated when corresponding pixels have sufficiently different grey values.

CHART

Special-purpose map designed for navigation or to present specific data or information. The term "chart" is applied chiefly to maps made primarily for nautical and aeronautical navigation, and to maps of the heavens, although the term is sometimes used to describe other special-purpose maps.

  • Chart, Aeronautical: Charts designed to meet requirements of aerial navigating, produced in several series, each on a specified map projection and differing in scale, format, and content, for use as dictated by type of aircraft and whether flight is to be conducted under visual or instrument flight rules.
  • Chart, Nautical: Representation of a portion of the navigable waters of the Earth and adjacent coastal areas on a specified map projection and designed specifically to meet requirements for marine navigation. Included on most nautical charts are depths of water, characteristics of the bottom, elevations of selected topographic features, general configurations and characteristics of the coast, the shoreline (usually the mean high water line), dangers, obstructions and aids to navigation limited tidal data, and information about magnetic variation in the charted area. 

CLOUD COVER PERCENTAGE

Cloud cover is measured by the percentage of an image obscured by clouds. Space Imaging Middle East will make best efforts to obtain coverage that meets customer requirements. Some geographic areas are more prone to clouds and haze than others, which will impact the time it takes to collect a particular area of interest.

COLOR

There are three "types" of color products available: Natural, False Color (Infrared), and Multispectral.

  • Natural: also known as "true" color, is composed of three primary colors of the visible spectrum (blue, green, red (0.4-0.7 micrometers)). When properly exposed/processed, the color rendition closely approximates the original scene as viewed by the human eye, thus the term Natural Color.
  • False Color (Infrared): when an image is processed, the resulting colors will be unnatural or false for most objects. Because of this, color-infrared film is sometimes called false-color film. For example, vigorous vegetation is displayed in intense red/pink tones rather than green.
  • Multispectral: imagery that is simultaneously collected in multiple wavelengths (bands) with a single sensor that operates in the visible and infrared spectral regions. This usually uses less than 10 spectral bands (more than 10 spectral bands is referred to as hyperspectral).

COLOR SEPARATION

Process of preparing a separate drawing, engraving, or negative for each color required in the printing production of a map or chart.

COLOR-INFRARED IMAGERY

Also called “false color” imagery, designed to differentiate between colors rather than reproduce them accurately. A tool to study landforms, vegetation health patterns, environmental pollution, and other effects of human activities on the planet’s surface.

COMPILATION

Preparation of a new or revised map or chart, or portion thereof, from existing maps, aerial photographs, field surveys, and other sources. 

CONTINUOUS TONE

Image not broken into dots by photographic screen; contains unbroken gradient tones from black to white, and may be either in negative or positive form. Aerial photographs are examples of continuous-tone prints. Contrasted with halftone (screened) and line copy.

CONTOUR

Imaginary line on ground, all points of which are at the same elevation above or below a specific datum.

CONTOUR INTERVAL

Difference in elevation between two adjacent contours.

CONTROL MAPPING

Points of established position or elevation, or both, which are used to fix references in positioning and correlating map features. Fundamental control is provided by stations in the national networks of triangulation and traverse (horizontal control) and leveling (vertical control). Usually it is necessary to extend geodetic surveys, based on fundamental stations, over the area to be mapped, to provide a suitable density and distribution of control points. Supplemental control points are those needed to relate the aerial photographs used for mapping with the system of ground control. These points must be positively photoidentified; that is, the points must be positively correlated with their images on the photographs.

CONTROL POINT

Points and/or cells which are used to establish map coordinate control for un-georeferenced objects. In the manual mosaic process, a control point is a feature in a piece of the mosaic (such as a road intersection) for which the map coordinates are known. In the raster-to-vector calibration process, a control point is a feature that is co-located between the un-georeferenced raster object, and the georeferenced vector object overlay. A control point may be something like a bend in a river or a road intersection that shows on both a raster object and an overlying vector object.

CONTROL POINT LIST

One type of map registration sub-object (Regist) that contains a paired list of map coordinates and cell coordinates.

CONTROL STATION

Point on the ground whose position (horizontal or vertical) is known and can be used as a base for additional survey work.

COORDINATES

Linear and (or) angular quantities that designate the position of a point in relation to a given reference frame.

Coordinates, Origin of: Points in a system of coordinates which serves as a zero point in computing the system's elements or in prescribing its use.