Interpolate ``param`` values to ``utc_time`` using indices nearest to
        (``latitude, longitude``).

        Parmaeters
        ----------
        latitude : float
            Latitude in degrees
        longitude : float
            Longitude in degrees
        utc_time : datetime.datetime or datetime.date
            Naive or UTC date or datetime to interpolate
        param : str
            Name of the parameter to interpolate from the data

        Returns
        -------
        Interpolated ``param`` value at (``utc_time, latitude, longitude``)

        Examples
        --------
        Use this to get a single value of a parameter in the data at a specific
        time and set of (latitude, longitude) coordinates.

        >>> from datetime import datetime
        >>> from pvlib.iotools import ecmwf_macc
        >>> data = ecmwf_macc.ECMWF_MACC('aod_tcwv_20121101.nc')
        >>> dt = datetime(2012, 11, 1, 11, 33, 1)
        >>> data.interp_data(38.2, -122.1, dt, 'aod550')

def interp_data(self, latitude, longitude, utc_time, param):
        """
        Interpolate ``param`` values to ``utc_time`` using indices nearest to
        (``latitude, longitude``).

        Parmaeters
        ----------
        latitude : float
            Latitude in degrees
        longitude : float
            Longitude in degrees
        utc_time : datetime.datetime or datetime.date
            Naive or UTC date or datetime to interpolate
        param : str
            Name of the parameter to interpolate from the data

        Returns
        -------
        Interpolated ``param`` value at (``utc_time, latitude, longitude``)

        Examples
        --------
        Use this to get a single value of a parameter in the data at a specific
        time and set of (latitude, longitude) coordinates.

        >>> from datetime import datetime
        >>> from pvlib.iotools import ecmwf_macc
        >>> data = ecmwf_macc.ECMWF_MACC('aod_tcwv_20121101.nc')
        >>> dt = datetime(2012, 11, 1, 11, 33, 1)
        >>> data.interp_data(38.2, -122.1, dt, 'aod550')
        """
        nctime = self.data['time']  # time
        ilat, ilon = self.get_nearest_indices(latitude, longitude)
        # time index before
        before = netCDF4.date2index(utc_time, nctime, select='before')
        fbefore = self.data[param][before, ilat, ilon]
        fafter = self.data[param][before + 1, ilat, ilon]
        dt_num = netCDF4.date2num(utc_time, nctime.units)
        time_ratio = (dt_num - nctime[before]) / self.delta_time
        return fbefore + (fafter - fbefore) * time_ratio