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doc: handling_geospatial_data

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Carlos Matallín 2015-10-28 12:37:51 +01:00
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doc/handling_geospatial_data.md
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Handling geospatial data through the SQL API is easy! By default, *the_geom* is returned straight from the database, in a format called Well-Known Binary. There are a handful of ways you can transform your geometries into more useful formats.
The first, is to use the format=GeoJSON method described above. Others can be handled through your SQL statements directly. For example, enclosing your the_geom in a function called [ST_AsGeoJSON](http://www.postgis.org/documentation/manual-svn/ST_AsGeoJSON.html) will allow you to use JSON for your data but a GeoJSON string for your geometry column only. Alternatively, using a the [ST_AsText](http://www.postgis.org/documentation/manual-svn/ST_AsGeoJSON.html) function will return your geometry as Well-Known Text.
<div class="code-title code-request with-result">ASGEOJSON</div>
### ST_AsGeoJSON
#### Call
```bash
https://{account}.cartodb.com/api/v2/sql?q=SELECT cartodb_id,ST_AsGeoJSON(the_geom) as the_geom FROM {table_name} LIMIT 1
```
<div class="code-title">RESULT</div>
#### Result
```javascript
{
time: 0.003,
@ -24,13 +27,16 @@ https://{account}.cartodb.com/api/v2/sql?q=SELECT cartodb_id,ST_AsGeoJSON(the_ge
}
```
### ST_AsText
#### Call
<div class="code-title code-request with-result">ASTEXT</div>
```bash
https://{account}.cartodb.com/api/v2/sql?q=SELECT cartodb_id,ST_AsText(the_geom) FROM {table_name} LIMIT 1
```
<div class="code-title">RESULT</div>
#### Result
```javascript
{
time: 0.003,
@ -48,7 +54,8 @@ More advanced methods exist in the PostGIS library to extract meaningful data fr
All data returned from *the_geom* column is in WGS 84 (EPSG:4326). You can change this quickly and easily on the fly using SQL. For example, if you desire geometries in the Hanoi 1972 (EPSG:4147) projection, you could [ST_Transform](http://www.postgis.org/docs/ST_Transform.html),
<div class="code-title code-request">ASTEXT</div>
### ST_Transform
```bash
https://{account}.cartodb.com/api/v2/sql?q=SELECT ST_Transform(the_geom,4147) FROM {table_name} LIMIT 1
```