Create and return a ``Point`` instance from a string containing
        latitude and longitude, and optionally, altitude.

        Latitude and longitude must be in degrees and may be in decimal form
        or indicate arcminutes and arcseconds (labeled with Unicode prime and
        double prime, ASCII quote and double quote or 'm' and 's'). The degree
        symbol is optional and may be included after the decimal places (in
        decimal form) and before the arcminutes and arcseconds otherwise.
        Coordinates given from south and west (indicated by S and W suffixes)
        will be converted to north and east by switching their signs. If no
        (or partial) cardinal directions are given, north and east are the
        assumed directions. Latitude and longitude must be separated by at
        least whitespace, a comma, or a semicolon (each with optional
        surrounding whitespace).

        Altitude, if supplied, must be a decimal number with given units.
        The following unit abbrevations (case-insensitive) are supported:

            - ``km`` (kilometers)
            - ``m`` (meters)
            - ``mi`` (miles)
            - ``ft`` (feet)
            - ``nm``, ``nmi`` (nautical miles)

        Some example strings that will work include:

            - ``41.5;-81.0``
            - ``41.5,-81.0``
            - ``41.5 -81.0``
            - ``41.5 N -81.0 W``
            - ``-41.5 S;81.0 E``
            - ``23 26m 22s N 23 27m 30s E``
            - ``23 26' 22" N 23 27' 30" E``
            - ``UT: N 39°20' 0'' / W 74°35' 0''``

def from_string(cls, string):
        """
        Create and return a ``Point`` instance from a string containing
        latitude and longitude, and optionally, altitude.

        Latitude and longitude must be in degrees and may be in decimal form
        or indicate arcminutes and arcseconds (labeled with Unicode prime and
        double prime, ASCII quote and double quote or 'm' and 's'). The degree
        symbol is optional and may be included after the decimal places (in
        decimal form) and before the arcminutes and arcseconds otherwise.
        Coordinates given from south and west (indicated by S and W suffixes)
        will be converted to north and east by switching their signs. If no
        (or partial) cardinal directions are given, north and east are the
        assumed directions. Latitude and longitude must be separated by at
        least whitespace, a comma, or a semicolon (each with optional
        surrounding whitespace).

        Altitude, if supplied, must be a decimal number with given units.
        The following unit abbrevations (case-insensitive) are supported:

            - ``km`` (kilometers)
            - ``m`` (meters)
            - ``mi`` (miles)
            - ``ft`` (feet)
            - ``nm``, ``nmi`` (nautical miles)

        Some example strings that will work include:

            - ``41.5;-81.0``
            - ``41.5,-81.0``
            - ``41.5 -81.0``
            - ``41.5 N -81.0 W``
            - ``-41.5 S;81.0 E``
            - ``23 26m 22s N 23 27m 30s E``
            - ``23 26' 22" N 23 27' 30" E``
            - ``UT: N 39°20' 0'' / W 74°35' 0''``

        """
        match = re.match(cls.POINT_PATTERN, re.sub(r"''", r'"', string))
        if match:
            latitude_direction = None
            if match.group("latitude_direction_front"):
                latitude_direction = match.group("latitude_direction_front")
            elif match.group("latitude_direction_back"):
                latitude_direction = match.group("latitude_direction_back")

            longitude_direction = None
            if match.group("longitude_direction_front"):
                longitude_direction = match.group("longitude_direction_front")
            elif match.group("longitude_direction_back"):
                longitude_direction = match.group("longitude_direction_back")
            latitude = cls.parse_degrees(
                match.group('latitude_degrees') or 0.0,
                match.group('latitude_arcminutes') or 0.0,
                match.group('latitude_arcseconds') or 0.0,
                latitude_direction
            )
            longitude = cls.parse_degrees(
                match.group('longitude_degrees') or 0.0,
                match.group('longitude_arcminutes') or 0.0,
                match.group('longitude_arcseconds') or 0.0,
                longitude_direction
            )
            altitude = cls.parse_altitude(
                match.group('altitude_distance'),
                match.group('altitude_units')
            )
            return cls(latitude, longitude, altitude)
        else:
            raise ValueError(
                "Failed to create Point instance from string: unknown format."
            )