determining the positional orientation (e.g., distance, azimuth) of one point or feature with respect to another.

Vertical Accuracy—The measure of the positional accuracy of a dataset with respect to a specified vertical datum. The vertical accuracy reporting standard (Accuracyz) is defined above.

Adjustment—The process of changing the values of a given set of quantities so that results calculated using the changed set will be better than those calculated using the original set. The concept of “better” is vague. The most common interpretation is that the sum of the squares of differences between results obtained by measurement and results obtained by calculation shall be a minimum. With this criterion, the method of least squares is the required process.

Aerial Triangulation (Aerotriangulation)—The process of measuring a number of points on overlapping images and/or ground control points to determine the most probable values of exterior orientation elements of aerial photographs. The output of this process includes ground space coordinates for all points measured on at least two images.

Arc-Second (or Second of Arc)—1/60 of a minute of arc, or 1/3,600 of a degree.

Attitude—The position of a body defined by the angles between the axes of the coordinate system of the body and the axes of an external coordinate system. In photogrammetry, the attitude is the angular orientation of a camera (roll, pitch, yaw), or of the photograph taken with that camera, with respect to some external reference system. With lidar (light detection and ranging) and IFSAR (interferometric synthetic aperture radar), the attitude is normally defined as the roll, pitch, and heading of the instrument at the instant an active pulse is emitted from the sensor.

Autocorrelation—A method for self-comparison of a string or sequence of numeric data.2

Bankline—A break in land surface slope adjacent to a stream that separates the steeper slope of the stream channel bank normally containing the flow from the flatter slope of the adjacent land area that is inundated only during floods.

Bare-Earth—Digital elevation data of the terrain, free from vegetation, buildings, and other man-made structures. Elevations of the ground.

Base Flood—A flood that has a 1-percent chance of being equaled or exceeded in any given year. Often called the 100-year flood.


Sackin, M. J., and D. F. Merriam. 1969. Autoassociation, a new geological tool. International Association for Mathematical Geology 1:8. Quoted in Jackson, R. L., and J. A. Jackson, eds. 1987. Glossary of Geology, 3rd edition, p. 45. Alexandria, Va.: American Geological Institute.

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