code: def _fit_strel_to_im_3d(im, strel, r, x, y, z):
      r
      elem = strel.copy()
      x_dim, y_dim, z_dim = im.shape
      x_min = x-r
      x_max = x+r+1
      y_min = y-r
      y_max = y+r+1
      z_min = z-r
      z_max = z+r+1
      if x_min < 0:
          x_adj = -x_min
          elem = elem[x_adj:, :, :]
          x_min = 0
      elif x_max > x_dim:
          x_adj = x_max - x_dim
          elem = elem[:-x_adj, :, :]
      if y_min < 0:
          y_adj = -y_min
          elem = elem[:, y_adj:, :]
          y_min = 0
      elif y_max > y_dim:
          y_adj = y_max - y_dim
          elem = elem[:, :-y_adj, :]
      if z_min < 0:
          z_adj = -z_min
          elem = elem[:, :, z_adj:]
          z_min = 0
      elif z_max > z_dim:
          z_adj = z_max - z_dim
          elem = elem[:, :, :-z_adj]
      ex, ey, ez = elem.shape
      im[x_min:x_min+ex, y_min:y_min+ey, z_min:z_min+ez] += elem
      return im
docs: r"""
      Helper function to add a structuring element to a 2D image.
      Used by RSA. Makes sure if center is less than r pixels from edge of image
      that the strel is sliced to fit.