IBM Visualization Data Explorer User's Reference

Category

Realization

Function

Maps scattered points onto a grid.

Syntax

output = AutoGrid(input, densityfactor, nearest,
                  radius,exponent,missing);

Inputs

Name	Type	Default	Description
input	field or vector list	none	field with positions to regrid
densityfactor	scalar or vector	1.0	densityfactor for grid
nearest	integer or string	1	number of nearest neighbors to use
radius	scalar	appropriate	radius from grid point to consider
exponent	scalar	1.0	weighting exponent
missing	value	no default	missing value to be inserted if necessary

Outputs

Name	Type	Description
output	field	regridded field

Functional Details

This module uses a specified set of scattered points (input) to assign data to every position of a grid. This module differs from Regrid in that you do not supply a grid; one is constructed automatically for you.

input	should be either (1) a field with a 1-, 2-, or 3-dimensional "positions" component or (2) a list of 1-, 2-, or 3-dimensional vectors. In the second case, the vectors are interpreted as positions.
densityfactor	specifies how to modify the automatically generated grid. By default the automatically generated grid will have approximately as many points as there are points in input, and each cell will be square. If densityfactor is a single scalar value, then there will be densityfactor times as many cells in each dimension. If densityfactor is a vector, then you can modify the number of cells in each dimension differentially.
nearest	must be an integer or the string "infinity." An integer value specifies the number of nearest points (to each grid point) to be used in computing an average data value for that grid point.
radius	By default, only those points within an automatically computed radius will be considered when assigning data values to grid positions. This automatically computed radius is twice the largest dimension of a cell in the grid. You can explicitly set the radius to a value measured in the units of the "positions" component of input. If you specify radius="infinity", then no cutoff in distance will be used; all points will contribute to the result at each grid point. AutoGrid attaches a "AutoGrid radius" attribute to output, with a value equal to the radius used, or the string "infinity".
exponent	The averaging method is a weighted average. The expression for this average is 1/radius(exponent). The default value is 1.0, reducing the expression to the reciprocal of the radius.
missing	is used when radius is set to a value other than "infinity." The parameter specifies how to treat those grid points for which no points in input occur within the specified radius. If missing is not set, the module creates an "invalid positions" component, and grid points with no assigned data value are invalidated. If missing is set, the data value is inserted for the missing data values. It must match the data component of input in rank, type, and shape. All components that are position-dependent are treated in the same way as the "data" component.

Components

Adds a "connections" component. The "positions" and "connections" components are those of grid while all components in input that depend on "positions" will be present in the output, modified by averaging.

Example Visual Programs

SIMPLE/AutoGrid.net
ConnectingScatteredPoints

See Also