presto-geospatial/src/main/java/io/prestosql/plugin/geospatial/GeoFunctions.java/GeoFunctions/stPointN
class GeoFunctions:    @SqlNullable
    @Description("Returns the vertex of a linestring at the specified index (indices started with 1) ")
    @ScalarFunction("ST_PointN")
    @SqlType(GEOMETRY_TYPE_NAME)
    public static Slice stPointN(@SqlType(GEOMETRY_TYPE_NAME) Slice input, @SqlType(INTEGER) long index)
    {
        OGCGeometry geometry = deserialize(input);
        validateType("ST_PointN", geometry, EnumSet.of(LINE_STRING));

        OGCLineString linestring = (OGCLineString) geometry;
        if (index < 1 || index > linestring.numPoints()) {
            return null;
        }
        return serialize(linestring.pointN(toIntExact(index) - 1));
    }