function [face, u, v] = h3d_coords_cell_to_avg_cube(face, i, j, buffer_width)
	
	assert(round(face)==face)
	assert(round(buffer_width)==buffer_width)
	assert(round(i)==i)
	assert(round(j)==j)
	assert( (face>=1) && (face<=6))
	assert( (i>=1) && (i <= buffer_width))
	assert( (j>=1) && (j <= buffer_width))
	
	
	% convert i from (1,n) to [0,1]
	u = (i-0.5) / buffer_width;
	% convert [0, 1] to [-1 1]
	u = u * 2 - 1;
	
	% same for v
	v = (j-0.5) / buffer_width;
	v = v * 2 - 1;