numeric. If type=circle, the radius of the circle (in units of the crs). If type=rectangle the dimension of the rectangle (one or two numbers). If type=Gauss the size of sigma, and optionally another number to determine the size of the matrix returned (default is 3*sigma)
type
character indicating the type of filter to be returned
fillNA
logical. If TRUE, zeros are set to NA such that they are ignored in the computations. Only applies to type="circle"