This topic describes the ST_HMTStats function. This function calculates the statistical values of heatmap tiles for being used during rendering.
Syntax
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);Return values
The statistical values of heatmap tiles are returned. The following parameters are included:
Parameter | Description |
min | The minimum value. |
max | The maximum value. |
mean | The average value. |
sum | The sum of values. |
count | The total number of statistical values. |
std | The standard deviation. |
median | The median value. |
mode | The mode. |
percentile | The array of percentile values. A total of 100 percentile values are included. |
Parameters
Parameter | Description |
hmt | The heatmap tile binary based on protobuf. |
factor | The sampling ratio, indicating the number of values used in each statistical calculation. For example, a factor of 4 indicates that four values are used in each statistical calculation. |
Description
This function calculates the statistical values of heatmap tiles for being used during rendering. Heatmap tiles are generated by using the ST_AsHMT function.
Examples
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}