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abelvm 2016-06-03 17:32:39 +02:00
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commit 73d38bbbaa
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60
doc/07_gravity.md
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## Gravity Model ## Gravity Model
### CDB_Gravity() ### CDB_Gravity(t_id bigint[], t_geom geometry[], t_weight numeric[], s_id bigint[], s_geom geometry[], s_pop numeric[], target bigint, radius integer, minval numeric DEFAULT -10e307)
The Gravity Model is derived from newtons law of gravity and is used to estimate the degree of interaction between two places Gravity Models are derived from Newton's Law of Gravity and are used to predict the interaction between a group of populated areas (sources) and a specific target among a group of potential targets, in terms of an attraction factor (weight)
**CDB_Gravity** is based on the model defined in *Huff's Law of Shopper attraction (1963)*
#### Arguments #### Arguments
| Name | Type | Description | | Name | Type | Description |
|------|------|-------------| |------|------|-------------|
| t_id | bigint[] | | | t_id | bigint[] | Array of targets ID |
| t_geom | geometry[] | | | t_geom | geometry[] | Array of targets' geometries |
| t_weight | numeric[] | | | t_weight | numeric[] | Array of targets's weights |
| s_id | bigint[] | | | s_id | bigint[] | Array of sources ID |
| s_geom | geometry[] | | | s_geom | geometry[] | Array of sources' geometries |
| s_pop | numeric[] | | | s_pop | numeric[] | Array of sources's population |
| target | bigint | | | target | bigint | ID of the target under study |
| radius | integer | | | radius | integer | Radius in meters around the target under study that will be taken into account|
| minval | numeric | | | minval (optional) | numeric | Lowest accepted value of weight, defaults to numeric min_value |
#### Returns #### Returns
| Column Name | Type | Description | | Column Name | Type | Description |
|-------------|------|-------------| |-------------|------|-------------|
| the_geom | Numeric | | | the_geom | geometry | Geometries of the sources within the radius |
| source_id | bigint | | | source_id | bigint | ID of the source |
| target_id | bigint | | | target_id | bigint | Target ID from input |
| dist | Numeric | | | dist | numeric | Distance in meters source to target (if not points, distance between centroids) |
| n | Numeric | | | h | numeric | Probability of patronage |
| hpop | NUMERIC | | | hpop | numeric | Patronaging population |
#### Example Usage #### Example Usage
```sql ```sql
SELECT CDB_GRAVITY (); with t as (
SELECT
array_agg(cartodb_id::bigint) as id,
array_agg(the_geom) as g,
array_agg(coalesce(gla,0)::numeric) as w
FROM
abel.centros_comerciales_de_madrid
WHERE not no_cc
),
s as (
SELECT
array_agg(cartodb_id::bigint) as id,
array_agg(center) as g,
array_agg(coalesce(t1_1, 0)::numeric) as p
FROM
sscc_madrid
)
select
g.the_geom,
trunc(g.h,2) as h,
round(g.hpop) as hpop,
trunc(g.dist/1000,2) as dist_km
FROM t, s, CDB_Gravity1(t.id, t.g, t.w, s.id, s.g, s.p, newmall_ID, 100000, 5000) g
``` ```

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src/pg/test/expected/07_gravity_test.out
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the_geom | h | hpop | dist
--------------------------------------------+-------------------------+--------------------------+----------------
01010000001361C3D32B650140DD24068195B34440 | 1.51078258369747945249 | 12.08626066957983561994 | 4964.714459152
01010000002497FF907EFB0040713D0AD7A3B04440 | 98.29730954183620807430 | 688.08116679285345652007 | 99.955141922
0101000000A167B3EA733501401D5A643BDFAF4440 | 63.70532894711274639196 | 382.23197368267647835174 | 2488.330566505
010100000062A1D634EF380140BE9F1A2FDDB44440 | 35.35415870080995954879 | 176.77079350404979774397 | 4359.370460594
010100000052B81E85EB510140355EBA490CB24440 | 33.12290506987740864904 | 132.49162027950963459615 | 3703.664449828
0101000000C286A757CA320140736891ED7CAF4440 | 65.45251754279248087849 | 196.35755262837744263547 | 2512.092358644
01010000007DD0B359F5390140C976BE9F1AAF4440 | 62.83927792471345639225 | 125.67855584942691278449 | 2926.25725244
0101000000D237691A140D01407E6FD39FFDB44440 | 53.54905726651871279586 | 53.54905726651871279586 | 3744.515577777
(8 rows)

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src/pg/test/sql/07_gravity_test.sql
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select * form CDB_Gravity() WITH t AS (
SELECT
ARRAY[1,2,3] AS id,
ARRAY[7.0,8.0,3.0] AS w,
ARRAY[ST_GeomFromText('POINT(2.1744 41.4036)'),ST_GeomFromText('POINT(2.1228 41.3809)'),ST_GeomFromText('POINT(2.1511 41.3742)')] AS g
),
s AS (
SELECT
ARRAY[10,20,30,40,50,60,70,80] AS id,
ARRAY[800, 700, 600, 500, 400, 300, 200, 100] AS p,
ARRAY[ST_GeomFromText('POINT(2.1744 41.403)'),ST_GeomFromText('POINT(2.1228 41.380)'),ST_GeomFromText('POINT(2.1511 41.374)'),ST_GeomFromText('POINT(2.1528 41.413)'),ST_GeomFromText('POINT(2.165 41.391)'),ST_GeomFromText('POINT(2.1498 41.371)'),ST_GeomFromText('POINT(2.1533 41.368)'),ST_GeomFromText('POINT(2.131386 41.41399)')] AS g
)
SELECT
g.the_geom,
g.h,
g.hpop,
g.dist
FROM
t,
s,
CDB_Gravity(t.id, t.g, t.w, s.id, s.g, s.p, 2, 100000, 3) g;