Terms starting with R

RADIAL-LINE PLOTTING

Determination of the location of points by the successive intersection and resection of direction lines radiating from the radial centers of overlapping aerial photographs. 

RADIOMETRIC DISTORTIONS

Distortions in imagery caused by variations in brightness and reflectance or spectral content.

RAW DATA

Unaltered, unprocessed satellite imagery data.

RECTIFICATION, DIFFERENTIAL

The process of scanning and reprojecting a photograph onto a horizontal plane in differential elements to remove displacements caused by tilt and relief. The process may be accomplished by any one of a number of instruments developed specifically for the purpose.

RECTIFICATION, SIMPLE

Projection of an aerial photograph (mathematically, graphically, or photographically) from its plane onto a horizontal plane by translation, rotation, and (or) scale change to remove displacement due to tilt of the camera.

RELIEF

Elevations and depressions of the land or sea bottom.

Relief Shading: Technique for making hypsography on a map appear three dimensional by the use of graded shadow effects. Generally, the features are shaded as though illuminated from the northwest.

REMOTE SENSING

The science of deriving information about the Earth’s land and water areas from images acquired at a distance. It usually relies upon measurement of electromagnetic energy reflected or emitted from the features of interest.

REPRESENTATIONAL FRACTION

Scale of a map or chart expressed as a fraction or ratio that relates unit distance on the map to distance measured in the same unit on the ground. 

REPRODUCTION

Summation of all processes involved in printing copies from an original drawing. A printed copy of an original drawing made by the processes of reproduction.

RESAMPLING METHOD

Geometric distortions are a result of the motions of the sensor, the spacecraft and the Earth. Corrections to these distortions are calculated and applied to the raw imagery data by resampling to produce a smooth consistent product. This necessary correction results in the radiometry of the output possibly being affected during the process. The choice of resampling method is best determined by the intended use of the data. Two resampling methods are available for image products, Cubic Convolution (CC) and Nearest Neighbor (NN). 

  • CC uses a neighborhood of 16 pixels from the raw imagery to calculate the brightness value of the final image product. CC provides a sharp image, with the least amount of geometric distortion and minimal radiometric distortion. This is ideal if the output product is to be used for mapping purposes or if it is necessary that the various layers fit well together when merging data sets.
  • NN uses the nearest neighbor pixel from the raw imagery to determine the brightness value in the final image product. The use of NN offers increased radiometric fidelity. NN should be considered if the integrity of the original radiometric values is extremely important.

RESOLUTION

A measure of the smallest linear separation between two objects that can be resolved by the sensor. For example, the smallest detectable, albeit unidentifiable, feature that the IKONOS 1-meter sensor can detect is 1 meter in diameter in photographs and 1 meter square in digital data.

REVISIT CAPABILITY

The frequency with which a satellite is able to fly over the same geographic area to repeatedly capture imagery.