ST_HMTStats - ApsaraDB RDS

計算熱力圖瓦片統計值資訊，方便在渲染時使用。

文法

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);

傳回值

返回熱力圖瓦片統計值資訊記錄，欄位說明如下：

欄位名稱	描述
min	最小值。
max	最大值。
mean	平均值。
sum	資料之和。
count	資料個數。
std	標準差。
median	中位元。
mode	眾數。
percentile	百分比數組。總共100個數值，表示每個百分比對應的數值。

參數

參數名稱	描述
hmt	基於protobuf表示的HMT二進位。
factor	採樣比例，即每多少個資料進行統計計算。例如，factor為4，表示每4個值進行統計。

描述

計算熱力圖瓦片統計值資訊，方便在渲染時使用。熱力圖瓦片需要通過ST_AsHMT函數產生。

樣本

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}