>dframe</code> is used to find the x-coordinate). The default
value is <code>NULL</code>.</p></dd>


<dt>ycoord</dt>
<dd><p>Character value providing name of the y-coordinate variable in
the <code>dframe</code> data frame.  For a two-stage sample, the y-coordinate
variable identifies stage two y-coordinates.  Note that y-coordinates are
required for calculation of the local mean variance estimator.  If <code>dframe</code>
is an <code>sf</code> object, this argument is not required (as the geometry column
in