PostGIS 3 瓦片提取函数 ST_TileEnvelope

作者

digoal

日期

2019-08-19

标签

PostgreSQL , PostGIS , 瓦片

背景

原文

https://info.crunchydata.com/blog/waiting-for-postgis-3-st_tileenvelopezxy

With the availability of MVT tile format in PostGIS via ST_AsMVT(), 越来越多用户使用PostGIS存储并直接产生地图瓦片。

Tile coordinates consist of three values:

• zoom, the level of the tile pyramid the tile is from
• x, the coordinate of the tile at that zoom, counting from the left, starting at zero
• y, the coordinate of the tile at that zoom, counting from the top, starting at zero

PostGIS 3提供了提取瓦片的函数ST_TileEnvelope，输入参数为金字塔图层的层级、x轴编号、y轴编号，瓦片空间。输出为指定x,y位置的瓦片（一个瓦片的像素为256*256）

https://en.wikipedia.org/wiki/Tiled_web_map

geometry ST_TileEnvelope(integer tileZoom, integer tileX, integer tileY, geometry bounds=SRID=3857;LINESTRING(-20037508.342789 -20037508.342789,20037508.342789 20037508.342789));

这个函数默认使用Spherical Mercator坐标，https://en.wikipedia.org/wiki/Web_Mercator_projection

例子

1、使用默认坐标

```
SELECT ST_AsText( ST_TileEnvelope(2, 1, 1) );

st_astext

POLYGON((-10018754.1713945 0,-10018754.1713945 10018754.1713945,0 10018754.1713945,0 0,-10018754.1713945 0))
```

2、使用非默认坐标

``` SELECT ST_AsText( ST_TileEnvelope(3, 1, 1, ST_MakeEnvelope(-180, -90, 180, 90, 4326) ) );

                  st_astext

POLYGON((-135 45,-135 67.5,-90 67.5,-90 45,-135 45))
```

3、创建非默认坐标

geometry ST_MakeEnvelope(float xmin, float ymin, float xmax, float ymax, integer srid=unknown);

参考

https://postgis.net/docs/manual-dev/ST_TileEnvelope.html

https://info.crunchydata.com/blog/waiting-for-postgis-3-st_tileenvelopezxy

https://postgis.net/docs/manual-dev/ST_MakeEnvelope.html

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