## Name

ST_IsValidReason — Returns text stating if a geometry is valid, or a reason for invalidity.

## Synopsis

`text ST_IsValidReason(`geometry geomA`)`;

`text ST_IsValidReason(`geometry geomA, integer flags`)`;

## 설명

Returns text stating if a geometry is valid, or if invalid a reason why.

Useful in combination with ST_IsValid to generate a detailed report of invalid geometries and reasons.

Allowed `flags` are documented in ST_IsValidDetail.

GEOS 모듈로 실행

Availability: 1.4

Availability: 2.0 version taking flags.

## 예시

```-- invalid bow-tie polygon
SELECT ST_IsValidReason(
'POLYGON ((100 200, 100 100, 200 200,
200 100, 100 200))'::geometry) as validity_info;
validity_info
--------------------------
Self-intersection[150 150]
```
```
--First 3 Rejects from a successful quintuplet experiment
SELECT gid, ST_IsValidReason(geom) as validity_info
FROM
(SELECT ST_MakePolygon(ST_ExteriorRing(e.buff), array_agg(f.line)) As geom, gid
FROM (SELECT ST_Buffer(ST_Point(x1*10,y1), z1) As buff, x1*10 + y1*100 + z1*1000 As gid
FROM generate_series(-4,6) x1
CROSS JOIN generate_series(2,5) y1
CROSS JOIN generate_series(1,8) z1
WHERE x1
> y1*0.5 AND z1 < x1*y1) As e
INNER JOIN (SELECT ST_Translate(ST_ExteriorRing(ST_Buffer(ST_Point(x1*10,y1), z1)),y1*1, z1*2) As line
FROM generate_series(-3,6) x1
CROSS JOIN generate_series(2,5) y1
CROSS JOIN generate_series(1,10) z1
WHERE x1
> y1*0.75 AND z1 < x1*y1) As f
ON (ST_Area(e.buff)
> 78 AND ST_Contains(e.buff, f.line))
GROUP BY gid, e.buff) As quintuplet_experiment
WHERE ST_IsValid(geom) = false
ORDER BY gid
LIMIT 3;

gid  |      validity_info
------+--------------------------
5330 | Self-intersection [32 5]
5340 | Self-intersection [42 5]
5350 | Self-intersection [52 5]

--simple example
SELECT ST_IsValidReason('LINESTRING(220227 150406,2220227 150407,222020 150410)');

st_isvalidreason
------------------
Valid Geometry

```