ST_HMTStats_云数据库 RDS(RDS)-阿里云帮助中心

计算热力图瓦片统计值信息，方便在渲染时使用。

语法

record ST_HMTAsArray(bytea hmt, integer factor default 1, out float8 min, out float8 max, out float8 mean, out float8 sum , out float8 count , out float8 std, out float8 median, out float8 mode, out float8[] percentile);

返回值

返回热力图瓦片统计值信息记录，字段说明如下：

字段名称	描述
min	最小值。
max	最大值。
mean	平均值。
sum	数据之和。
count	数据个数。
std	标准差。
median	中位数。
mode	众数。
percentile	百分比数组。总共100个数值，表示每个百分比对应的数值。

参数

参数名称	描述
hmt	基于protobuf表示的HMT二进制。
factor	采样比例，即每多少个数据进行统计计算。例如，factor为4，表示每4个值进行统计。

描述

计算热力图瓦片统计值信息，方便在渲染时使用。热力图瓦片需要通过ST_AsHMT函数生成。

示例

CREATE TABLE test_table AS
SELECT i num,
    ST_setSRID(st_makepoint((i-0.5)::numeric, (i-0.5)::numeric), 4326) geom,
    i*100::int4 weight,
    i*i*i::float8 volume
FROM generate_series(1, 10) i;

SELECT (ST_HMTstats(ST_AsHMT(the_geom,
    ST_MakeEnvelope(0, 0, 10, 10),
    10,
    10))).*
FROM test_table;

------------------
 min | max | mean | sum | count | std | median | mode | percentile
   0 |   2 | 0.19 |  19 |   100 | 0.5778408085277467 |      0 |    0 | {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,1,2,2,2,2,2,2,2,2}

-- factor set to 4
SELECT (ST_HMTstats(ST_AsHMT(the_geom,
    ST_MakeEnvelope(0, 0, 10, 10),
    10,
    10),4)).*
FROM test_table;

------------------
 min | max | mean | sum | count | std | median | mode | percentile
   0 |   2 | 0.16 |   4 |    25 | 0.5425863986500215 |      0 |    0 | {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,2,2,2,2,2,2,2}