Filter Grid

Filter: creates a new grid, leaving the original unchanged. This cannot operate on the original grid in place because it requires the unchanged neighborhood values.

Filter grid with .fil file--filter the current grid, using a matrix with custom values.
Enter value for number of pixels to go out in each direction--for instance a value of 2 will create a 5x5 filter. (this allows much bigger filters than the Filter grid command, but will be slower)
- Mode (majority filter)--only for byte grids, replaces the value with the most common one in the 3x3 or 5x5 neighborhood.
- Median filter: Replaces with median value in the box.
- Mean filter: Replaces with mean (average) value in the box.
- Minimum filter: Replaces with lowest value in the box.
- Maximum filter: Replaces with highest value in the box.
- Parametric isotropic smoothing: recommended by Hengl and Evans (2008, after Sharry and others, 2002) before computing curvature or other derivatives.
- Vector average: smooths circular data like aspects.
- Std Deve in box: Replaces with the standard deviation in the region
- Sum in box: sums values within box.
- Filled neighborhood: Pick minimum number of points that must be present in the region. Points not meeting the criteria will be removed from the grid.
- Number immediate neighbors: new grid with the number of immediate neighbors in a specified region size
- Isolated values
- Edges
- RGB grid fill holes
- Detrend DEM/grid: select a radius in pixels for a square mean filter, and a new DEM will be creating subtracting the result of the filter from the original DEM elevation

"Filter grids to edge", set on Grids tab of the Options form, allows filtering to the edge of data set, even if the filter should require points outside the grid limits.

Filtering theory

Last revision 7/112022