根据MEAN-MAX算法，计算出每个时间段内的均值的最大值。

语法

SETOF record ST_trajAttrsMeanMax(trajectory traj, cstring attr_field_name, out interval duration, out float8 max);

参数

参数名称 描述
traj 轨迹对象。
attr_field_name 指定的属性名称。

描述

Mean-Max 算法通过一个滑动窗口，分别计算出落入该窗口的属性值的平均值，再求出所有均值的最大值。

该函数仅对integer和float类型的属性值有效。属性值不能为NULL。

示例

With traj AS (
    Select ST_makeTrajectory('STPOINT', 'LINESTRING(1 1, 6 6, 9 8, 10 12)'::geometry,
    ARRAY['2010-01-01 11:30'::timestamp, '2010-01-01 12:30', '2010-01-01 13:30', '2010-01-01 14:30'],
    '{"leafcount":4, "attributes":{"velocity": {"type": "float", "length": 8,"nullable" : true,"value": [120.0, 130.0, 140.0, 120.0]}, "power": {"type": "float", "length": 4,"nullable" : true,"value": [120.0, 130.0, 140.0, 120.0]}}}') a)
Select st_trajAttrsMeanMax(a, 'velocity') from traj;
 st_trajattrsmeanmax 
---------------------
 ("@ 1 hour",135)
 ("@ 2 hours",130)
 ("@ 3 hours",127.5)
(3 rows)

 With traj AS (
    Select ST_makeTrajectory('STPOINT', 'LINESTRING(1 1, 6 6, 9 8, 10 12)'::geometry,
    ARRAY['2010-01-01 11:30'::timestamp, '2010-01-01 12:30', '2010-01-01 13:30', '2010-01-01 14:30'],
    '{"leafcount":4, "attributes":{"velocity": {"type": "float", "length": 8,"nullable" : true,"value": [120.0, 130.0, 140.0, 120.0]}, "power": {"type": "float", "length": 4,"nullable" : true,"value": [120.0, 130.0, 140.0, 120.0]}}}') a)
Select (st_trajAttrsMeanMax(a, 'velocity')).* from traj;
 duration |  max  
----------+-------
 01:00:00 |   135
 02:00:00 |   130
 03:00:00 | 127.5
(3 rows)