A
accuracy The closeness of an estimated value (for example, measured or computed) to a standard or accepted (true) value of a particular quantity. See precision.
•
absolute accuracy A measure that accounts for all systematic and random errors in a dataset. Absolute accuracy is stated with respect to a defined datum or reference system.
•
accuracyr (ACCr) The National Standards for Spatial Data Accuracy (NSSDA) (Federal Geographic Data Committee, 1998) reporting standard in the horizontal component that equals the radius of a circle of uncertainty, such that the true or theoretical horizontal location of the point falls within that circle 95 percent of the time. ACCRMSErr=×17308..
•
accuracyz (ACCz) The NSSDA reporting standard in the vertical component that equals the linear uncertainty value, such that the true or theoretical vertical location of the point falls within that linear uncertainty value 95 percent of the time. ACCRMSEzz=×19600..
•
horizontal accuracy The horizontal (radial) component of the positional accuracy of a dataset with respect to a horizontal datum, at a specified confidence level. See accuracyr.
•
local accuracy The uncertainty in the coordinates of points with respect to coordinates of other directly connected, adjacent points at the 95-percent confidence level.
•
network accuracy The uncertainty in the coordinates of mapped points with respect to the geodetic datum at the 95-percent confidence level.
•
positional accuracy The accuracy at the 95-percent confidence level of the position of features, including horizontal and vertical positions, with respect to horizontal and vertical datums.
•
relative accuracy A measure of variation in point-to-point accuracy in a data set. In lidar, this term may also specifically mean the positional agreement between points within a swath, adjacent swaths within a lift, adjacent lifts within a project, or between adjacent projects.
•
vertical accuracy The measure of the positional accuracy of a data set with respect to a specified vertical datum, at a specified confidence level or percentile. See accuracyz.
aggregate nominal pulse density (ANPD) A variant of nominal pulse density that expresses the total expected or actual density of pulses occurring in a specified unit area resulting from multiple passes of the light detection and ranging (lidar) instrument, or a single pass of a platform with multiple lidar instruments, over the same target area. In all other respects, ANPD is identical to nominal pulse density (NPD). In single coverage collection, ANPD and NPD will be equal. See aggregate nominal pulse spacing, nominal pulse density, nominal pulse spacing.
aggregate nominal pulse spacing (ANPS) A variant of nominal pulse spacing that expresses the typical or average lateral distance between pulses in a lidar dataset resulting from multiple passes of the lidar instrument, or a single pass of a platform with multiple lidar instruments, over the same target area. In all other respects, ANPS is identical to nominal pulse spacing
18 Lidar Base Specification
(NPS). In single coverage collections, ANPS and NPS will be equal. See aggregate nominal pulse density, nominal pulse density, nominal pulse spacing.
artifacts An inaccurate observation, effect, or result, especially one resulting from the technology used in scientific investigation or from experimental error. In bare-earth elevation models, artifacts are detectable surface remnants of buildings, trees, towers, telephone poles or other elevated features; also, detectable artificial anomalies that are introduced to a surface model by way of system specific collection or processing techniques. For example, corn-row effects of profile collection, star and ramp effects from multidirectional contour interpolation, or detectable triangular facets caused when vegetation canopies are removed from lidar data.
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, 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.
