New Variogram General Properties
The New Variogram dialog is used to create a new variogram. Click Grids | New Grid | Variogram |New Variogram and select a data file to open the New Variogram dialog.
Use the New Variogram command to open the New Variogram dialog. The General page is used to define the variogram grid.
You can set the variogram grid properties on the General page in the New Variogram dialog.
The Variogram Grid group contains the maximum lag distance, angular divisions, and the radial divisions settings for the variogram grid, as pictured on the right side of the group.
The picture to the right of the edit controls depicts the specified variogram grid. However, to make the picture legible, the number of concentric circles drawn is equal to the number of radial divisions divided by ten. The number of radial spokes drawn is equal to the number of angular divisions divided by ten.
Max Lag Distance
Max Lag Distance specifies the largest separation distance contained in the variogram grid. Any pairs separated by more than the maximum lag distance are not included in the variogram grid. The default value of the Max Lag Distance is one third the diagonal extent of the data rounded down at the second significant figure (i.e. 1.2345 becomes 1.2).
The Angular Divisions specify the number of angular divisions: i.e. the number of spaces between "spokes" in the variogram grid. 0° is located on the positive X axis, not the positive Y axis (azimuth). The angular divisions only go from 0° to 180°, and not all the way back around to 360°. If a vector were drawn from the first point in the pair to the second point in the pair, the arrow symbol would point to one direction in the polar grid. In Surfer, the first point is the point with the smaller Y value and the second point is the point with the larger Y value. As such, the lower half of the variogram grid is empty and unnecessary. The experimental variogram for any direction between 180° and 360° can be computed from the upper half of the grid using the inherent symmetry of the variogram. The default value of 180 makes each variogram grid cell span 1° of arc.
The Radial Divisions specify the number of concentric circles in the variogram grid. The default value is 100. Keep in mind that increasing the number of Angular Divisions and Radial Divisions increases the amount of memory required to store the grid. See The Variogram Grid for more information on memory requirements.
Click in the Generate Report check box to create a report of the data, including statistics. For more information about the contents of the report, see Reports.