## 语法

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

## 参数

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。

## 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)``````