Synopsis
		sfextract < in.rsf > out.rsf head=head.rsf xkey= ykey= interp=2 xk= yk=

Parameters
		file head= auxiliary input file name   int interp=2 [1,2] interpolation method, 1: nearest neighbor, 2: bi-linear   string xk= x key name   int xkey= x key number (if no xk), default is sx   string yk= y key name   int ykey= y key number (if no yk), default is sy

Used In
		JSG          shape/rain