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Variograms


Variogram Data

This command is used to calcuate the semi-variogram for the data set. A covariance table is generated for the variation in z values between all data points. The covariance is measured between pairs of data points of similar distance apart, grouped by a specified cell width. The cell width to use for the "binning" of the distances between data points is specified.

For example, when the cell width is 1.0 with a Mercator projection, the z values of all data points 1.0-2.0 km apart will contribute to the covariance of the 1.0-2.0 km cell.

There are 1 or more parameters:
cell width - the cell width in user units.
angle - the angle in degrees for a directional variogram.
tolerance - the tolerance in degrees + or - of angle for a directional variogram.
robust - the robust calculation flag.
xyz matrix - a matrix containing the x, y, and z data as 3 columns.
or
x, y, and z vectors- 3 vectors containing the data to be plotted.

The command returns a n x 10 matrix with columns:
distance, semi_variance, count, covariance, correlation, mean_head, mean_tail, SD_head, SD_tail, and sample_variance.
Variogram_Data(cell width[,angle][,tolerance][,robust],xyz matrix );
Variogram_Data(cell width[,angle][,tolerance][,robust],x vector, y vector, z vector );

data_projection("MERCATOR");
x = -1. 1 0 -1 1;
y = 1. 1 0 -1 -1;
z = 1 2 3 4 5.;
Variogram_Data(0.05,x,y,z);
Cell width: 0.050000
Variogram points: 4
Distance min: 157.425000, max: 314.875000
Semi-variance min: 0.500000, max: 5.000000
157.425 1.25 4 1.9375 1.830579 2.25 3.75 0.916667 0.916667 2.5
222.625 0.50 2 0.2500 2.388889 2.50 3.50 4.500000 4.500000 2.5
222.675 4.50 2 2.2500 1.500000 1.50 4.50 0.500000 0.500000 2.5
314.875 5.00 2 2.7500 3.500000 1.50 4.50 0.500000 0.500000 2.5

variogram_data(0.05,45,90,x,y,z)
Cell width: 0.050000
Variogram points: 4
Distance min: 157.425000, max: 314.875000
Semi-variance min: 0.500000, max: 5.000000
157.425 1.25 4 1.9375 1.830579 2.25 3.75 0.916667 0.916667 2.5
222.625 0.50 2 0.2500 2.388889 2.50 3.50 4.500000 4.500000 2.5
222.675 4.50 2 2.2500 1.500000 1.50 4.50 0.500000 0.500000 2.5
314.875 5.00 2 2.7500 3.500000 1.50 4.50 0.500000 0.500000 2.5


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Last Modified : 2003-11-19