Use the Search tab of the Gridding form to define the shape, size and other characteristics of a search ellipse. Search options are not applicable to the MINIMUM CURVATURE, INDISTPOW + MINIMUM CURVATURE and NEAREST NEIGHBOUR methods.
Use points outside grid limits
(Optional) Select this option if you want to include points outside the grid surafce limits (but within the search ellipse).
Search Area
Search shape
You can select either a CIRCLE or an ELLIPSE as the search area shape. A circle is more usual unless the data is concentrated in some way that suits an ellipse better.
Search radius
When the Search shape is CIRCLE, enter the radius of the data search circle in X axis units.
X and Y Search radius
Enter the radius of search ellipse in the X and T directions. In general, a good starting point is to make the radius about 1.5 to 2 times the grid surface spacing.
Search skew
A search ellipse can be skewed if an examination of the raw data suggests this may improve the fit of the grid surface to the data. Enter the rotation of the search ellipse in degrees, measured clockwise from zero at the top of the screen.
Sectors
This number defines how many parts the search shape will be divided into for the data search.
The maximum number of points is multiplied by the number of sectors to determine how many data points can be used within the overall search shape. For example, if you choose FOUR sectors, the search shape is a circle, and the maximum number of points is 15, then the nearest 15 data points in each quadrant will be used, totalling 60 points.
This option can eliminate the clustering effects of irregularly spaced data.
Max points per sector
The maximum number of points to be used in the estimation of a block value. This input is compulsory. Enter a value which is greater than zero. The maximum allowable value is 150.
When more than one sector is defined, each sector can independently use up to the maximum number of points.
(e.g. 150 pts x 4 sectors = 600 pts)
If more than the maximum number of points is found within a sector the closest points are used.
Minimum distance
Enter a minimum distance in X data (axis) units. The estimation algorithm will use this as the distance between a data point and the centre of the block being estimated.
This deals with the situation where the value of a data point very close to the centre of the block being estimated becomes in effect the value of the block, overpowering the effect of other data points found within the search ellipse.
If the distance between a data point and the block centre is less than the value entered here, the value entered will be used instead of the true distance.
Duplicate points
Choose how the function should deal with Duplicate points: IGNORE, AVERAGE or take the MAXIMUM or MINIMUM value. Duplicate points are those with the same coordinates but different data values. See: Duplicate Points
SEE ALSO