Defining a Neighborhood

Inverse distance, ordinary kriging, and indicator kriging all require a neighborhood definition for estimating concentration values at a point. A neighborhood is defined as an area around the point in which data values will be used to estimate the concentration value. Data values outside the neighborhod will be excluded.

The neighborhood is always defined by a search ellipse that can be manipulated in shape and size to include or exclude various data. The parameters which control the shape and size of the search ellipse are entered in the Geo tab of the Control Panel.

The parameters Major Radius, Minor Radius, and XY Angle control the size and shape of the search ellipse.

XY Angle

The angle or direction of the major elllipse axis. This angle is measured clockwise from the positive Y axis (0 deg is North). The minor elliptical axis is perpendicular to the major axis.

Major Radius

The radius of the ellipse along the major axis.

Minor Radius

The radius of the ellipse along the minor axis.

The following schematic demonstrates the roles of these parameters in the XY plane.

For three-dimensional data, the ellipse becomes an ellipsoid. The following parameters, in addition to those listed above, describe the search ellipsoid in 3D space.

Z Angle

The angle or dip below the XY plane at the point of estimation. This angle is measured as negative degrees below the plane.

Vertical Radius

Often referred to as the Z minor radius, this is the radius of the ellipsoid in the minor direction.

Rotation

The parameters described to this point fully form the body of the ellipsoid in 3D space. The rotation parameter then rotates this ellipsoid about the major axis the specified number of degrees.

The following schematic shows how the ellipsoid is affected by the Z Angle and Vertical Radius parameters in a cross sectional view.

The following view shows the effect of the rotation parameter on the ellipsoid body. This view is along the major elliptical axis. The rotation angle rotates the two orthogonal directions clockwise relative to the major elliptical axis when looking toward the origin.

The following parameters define the search criteria within the search ellipse.

Min Data

The minimum number of data required before estimating the concentration. If this minimum is not met, SADA returns an unestimated value. You will be notified of the number of unestimated values. These values appear as empty spaces in the plot.

Max Data

The maximum number of data to use in estimating a point.

Octant

The ellipsoid is divided into quadrants, four if two dimensional, eight if three-dimensional. If the Octant value is greater than zero and there are fewer data points than the octant value in each quadrant of the ellipsoid, then the point will not be estimated.

The power parameter is associated with the Inverse distance Method and has no bearing on the search scheme.