You can control the parameters used to create the grid from the Data Source Properties or using the "Grid Parameters" tab in the Data Subset panel of the Field Selector:
You can set the grid spacing as follows:
Specify the grid spacing if not using automatic calculation.
Set the number of passes for the Barnes analysis to do 4 passes recommended for analysing fields where derivative estimates are important (Ref: Barnes 1994b) 3 passes recommended for all other fields (with gain set to 1.0) (Ref: Barnes 1994c "Two pass Barnes Objective Analysis schemes now in use probably should be replaced by appropriately tuned 3pass or 4pass schemes") 2 passes only recommended for "quick look" type analyses.
Set the search radius (in grid units) for the weighting of points in determining the value at a specific grid point.
Factor by which scaleLength is reduced for the second pass. Should be in the range 0.2 to 1.0. Data are fitted more closely with a gain of 0.2 (at the expense of less overall accuracy over the entire grid); larger values smooth more. Suggested default: 1.0f Set the gain for each pass after the first.
You can use a model grid as a first guess field for the analysis. Select the "Grid Parameters (with first guess)" field and you will be prompted to select the gridded field to use for the first guess.