[R-sig-Geo] Sending raster:::aggregate a function with multiple parameters?

[Jonathan Greenberg]

R-sig-geo'ers:

I wanted to run aggregate on a *degree* based azimuth image, with a
"circ.mean" resampling.  Since you can't just average degrees and get
the right answer (e.g. the arithmetic mean of 359 degrees and 1
degrees is 180, but the "true" mean direction is 0), I adapted the
circ.mean function in CircStats to be used with aggregate.  My
question is, I'd like to be able to pass a "unit" argument to the
function, but I'm not sure how to do this.  Here's the code:

require(raster)
require(CircStats)
# require(STARStools)
# (Swap in some DEM for the following call, or download STARStools 0.4
or later from r-forge):
tahoe_lidar_bareearth <-
raster(system.file("external/tahoe_lidar_bareearth.tif",
package="STARStools"))
azimuth_raster <-
slopeAspect(tahoe_lidar_bareearth,out=c('aspect'),unit='degrees')

# Here is the adapted circ.mean function that adds na.rm and a "unit" field:

circ.mean.na.rm = function(x,unit="radians",na.rm=TRUE)
{	
	if(unit=="degrees")
	{
		x=rad(x)
	}
	
	if(na.rm)
	{
		x_mean=circ.mean(na.omit(x))
	} else
	{
		x_mean=circ.mean(x)
	}
	
	if(unit=="degrees")
	{
		x_mean=deg(x_mean)
	}
	return(x_mean)
}

# How do I now pass a unit argument to aggregate?
azimuth_raster_agg=aggregate(x=azimuth_raster,fact=fact,fun=circ.mean.na.rm)
# This call returns the wrong value, because I haven't passed "unit"
to circ.mean.na.rm() -- how do I do this from within aggregate?

--j