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‎201908/20190803_04.md‎

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## PostgreSQL PostGIS 3 st_asgeojson
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### 作者
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digoal
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### 日期
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2019-08-03
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### 标签
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PostgreSQL , PostGIS , geojson , record , feature , geometry
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----
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## 背景
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原文
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https://info.crunchydata.com/blog/postgis-3-geojson-st-asgeojson
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geojson是服务端与客户端geo数据传输等一种格式，格式参考RFC定义
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https://tools.ietf.org/html/rfc7946
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```
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2. GeoJSON Text . . . . . . . . . . . . . . . . . . . . . . . . 6
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3. GeoJSON Object . . . . . . . . . . . . . . . . . . . . . . . 6
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3.1. Geometry Object . . . . . . . . . . . . . . . . . . . . . 7
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3.1.1. Position . . . . . . . . . . . . . . . . . . . . . . 7
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3.1.2. Point . . . . . . . . . . . . . . . . . . . . . . . . 8
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3.1.3. MultiPoint . . . . . . . . . . . . . . . . . . . . . 8
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3.1.4. LineString . . . . . . . . . . . . . . . . . . . . . 8
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3.1.5. MultiLineString . . . . . . . . . . . . . . . . . . . 8
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3.1.6. Polygon . . . . . . . . . . . . . . . . . . . . . . . 9
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3.1.7. MultiPolygon . . . . . . . . . . . . . . . . . . . . 9
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3.1.8. GeometryCollection . . . . . . . . . . . . . . . . . 9
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3.1.9. Antimeridian Cutting . . . . . . . . . . . . . . . . 10
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3.1.10. Uncertainty and Precision . . . . . . . . . . . . . . 11
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3.2. Feature Object . . . . . . . . . . . . . . . . . . . . . 11
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3.3. FeatureCollection Object . . . . . . . . . . . . . . . .
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```
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PostGIS 3以前，st_asgeojson仅支持geometry输入，构造geojson格式比较麻烦
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http://postgis.net/docs/manual-2.5/ST_AsGeoJSON.html
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```
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text ST_AsGeoJSON(geometry geom, integer maxdecimaldigits=15, integer options=0);
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text ST_AsGeoJSON(geography geog, integer maxdecimaldigits=15, integer options=0);
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select row_to_json(fc)
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from (
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select
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'FeatureCollection' as "type",
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array_to_json(array_agg(f)) as "features"
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from (
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select
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'Feature' as "type",
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ST_AsGeoJSON(ST_Transform(way, 4326), 6) :: json as "geometry",
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(
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select json_strip_nulls(row_to_json(t))
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from (
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select
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osm_id,
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"natural",
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place
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) t
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) as "properties"
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from planet_osm_point
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where
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"natural" is not null
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or place is not null
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limit 10
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) as f
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) as fc;
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st_asgeojson
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-----------------------------------------------------------------------------------------------------------
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{"type":"FeatureCollection","features":[{"type":"Feature","geometry":{"type":"Point","coordinates":[23.569251,51.541599]},"properties":{"osm_id":3424148658,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.625174,51.511718]},"properties":{"osm_id":4322036818,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.613928,51.5417]},"properties":{"osm_id":242979330,"place":"hamlet"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.586361,51.563272]},"properties":{"osm_id":3424148656,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.605488,51.553886]},"properties":{"osm_id":242979323,"place":"village"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.6067,51.57609]},"properties":{"osm_id":242979327,"place":"village"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.636533,51.575683]},"properties":{"osm_id":5737800420,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.656733,51.518733]},"properties":{"osm_id":5737802397,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.672542,51.504584]},"properties":{"osm_id":242979320,"place":"hamlet"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.574094,51.63389]},"properties":{"osm_id":242979333,"place":"village"}}]}
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SELECT ST_AsGeoJSON(geom) from fe_edges limit 1;
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st_asgeojson
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-----------------------------------------------------------------------------------------------------------
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{"type":"MultiLineString","coordinates":[[[-89.734634999999997,31.492072000000000],
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[-89.734955999999997,31.492237999999997]]]}
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(1 row)
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```
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3以后，st_asgeojson支持record输入，默认第一列为geo类型，其他列的内容合并到properties中。
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http://postgis.net/docs/manual-dev/ST_AsGeoJSON.html
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text ST_AsGeoJSON(record feature, text geomcolumnname, integer maxdecimaldigits=15, boolean pretty_bool=false);
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The ST_AsGeoJSON(record) function looks at the input tuple, and takes the first column of type geometry to convert into a GeoJSON geometry. The rest of the columns are added to the GeoJSON features in the properties member.
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例子
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```
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SELECT ST_AsGeoJSON(subq.*) AS geojson
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FROM (
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SELECT ST_Centroid(geom), type, admin
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FROM countries
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WHERE name = 'Canada'
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) AS subq
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{"type": "Feature",
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"geometry": {
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"type":"Point",
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"coordinates":[-98.2939042718784,61.3764628013483]
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},
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"properties": {
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"type": "Sovereign country",
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"admin": "Canada"
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}
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}
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```
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http://postgis.net/docs/manual-dev/ST_AsGeoJSON.html
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```
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To build FeatureCollection:
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select json_build_object(
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'type', 'FeatureCollection',
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'features', json_agg(ST_AsGeoJSON(t.*)::json)
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)
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from ( values (1, 'one', 'POINT(1 1)'::geometry),
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(2, 'two', 'POINT(2 2)'),
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(3, 'three', 'POINT(3 3)')
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) as t(id, name, geom);
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{"type" : "FeatureCollection", "features" : [{"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]}, "properties": {"id": 1, "name": "one"}}, {"type": "Feature", "geometry": {"type":"Point","coordinates":[2,2]}, "properties": {"id": 2, "name": "two"}}, {"type": "Feature", "geometry": {"type":"Point","coordinates":[3,3]}, "properties": {"id": 3, "name": "three"}}]}
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To get Features as records:
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SELECT ST_AsGeoJSON(t.*)
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FROM (VALUES
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(1, 'one', 'POINT(1 1)'::geometry),
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(2, 'two', 'POINT(2 2)'),
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(3, 'three', 'POINT(3 3)'))
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AS t(id, name, geom);
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st_asgeojson
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-----------------------------------------------------------------------------------------------------------------
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{"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]}, "properties": {"id": 1, "name": "one"}}
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{"type": "Feature", "geometry": {"type":"Point","coordinates":[2,2]}, "properties": {"id": 2, "name": "two"}}
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{"type": "Feature", "geometry": {"type":"Point","coordinates":[3,3]}, "properties": {"id": 3, "name": "three"}}
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```
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## 参考
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https://info.crunchydata.com/blog/postgis-3-geojson-st-asgeojson
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<a rel="nofollow" href="http://info.flagcounter.com/h9V1" ><img src="http://s03.flagcounter.com/count/h9V1/bg_FFFFFF/txt_000000/border_CCCCCC/columns_2/maxflags_12/viewers_0/labels_0/pageviews_0/flags_0/" alt="Flag Counter" border="0" ></a>
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## [digoal's 大量PostgreSQL文章入口](https://github.com/digoal/blog/blob/master/README.md "22709685feb7cab07d30f30387f0a9ae")
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## [免费领取阿里云RDS PostgreSQL实例、ECS虚拟机](https://free.aliyun.com/ "57258f76c37864c6e6d23383d05714ea")
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‎201908/readme.md‎

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### 文章列表
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----
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##### 20190803_04.md [《PostgreSQL PostGIS 3 st_asgeojson》](20190803_04.md)
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##### 20190803_03.md [《PostgreSQL PostGIS 3 Hilbert Geometry Sorting - 空间排序算法优化》](20190803_03.md)
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##### 20190803_02.md [《PostgreSQL PostGIS overlap》](20190803_02.md)
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##### 20190803_01.md [《PostgreSQL PostGIS ST_AsMVT Performance 提升 - SQL提取地图矢量瓦片(Mapbox Vector Tile)》](20190803_01.md)

‎README.md‎

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### 所有文档如下
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----
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##### 201908/20190803_04.md [《PostgreSQL PostGIS 3 st_asgeojson》](201908/20190803_04.md)
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##### 201908/20190803_03.md [《PostgreSQL PostGIS 3 Hilbert Geometry Sorting - 空间排序算法优化》](201908/20190803_03.md)
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##### 201908/20190803_02.md [《PostgreSQL PostGIS overlap》](201908/20190803_02.md)
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##### 201908/20190803_01.md [《PostgreSQL PostGIS ST_AsMVT Performance 提升 - SQL提取地图矢量瓦片(Mapbox Vector Tile)》](201908/20190803_01.md)

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