function calcsurf, z, kx

degree=1

   s = size(z)
   nx = s(1)
   ny = s(2)
   m = nx * ny          ;# of points to fit
   n2=(degree+1)^2              ;# of coefficients to solve
   x = findgen(nx) # replicate(1., ny)   ;X values at each point
   y = replicate(1.,nx) # findgen(ny)

   return, kx(0,0)+x*kx(0,1)+y*kx(1,0)+x*y*kx(1,1)

	end