PostGIS 中的缓冲区（圆形）

【问题标题】：Buffers (Circle) in PostGISPostGIS 中的缓冲区（圆形）
【发布时间】：2018-10-03 16:56:31
【问题描述】：

我必须扩展正常的 GeoJSON 格式以添加一些不受支持的多边形，例如 Circle。

{
 "type": "Circle",
 "radius" : 0.001,
 "coordinates": [
        5.417075157165527,
       43.29129488122568
 ]
}

这是一个例子。坐标标记圆心，半径标记半径（以米为单位）。

在 PostGis Docs 和 Stackoverflow 上搜索，要绘制一个圆圈，您必须使用 ST_BUFFER。

所以我使用：

ST_Buffer(ST_GeomFromGeoJSON(<center of circle>),0.001, 'quad_segs=16')

你知道吗，这仅在 0,0（非洲附近）绘制一个圆圈。其他位置会添加扭曲，从而改变椭圆的形状。

我使用的是 4326。

我尝试过搜索（即使在这里），但我找不到简单地画一个圆避免投影或变换它的解决方案。

这里唯一的帖子是：How to create a circle in meters in postgis? 但它很旧，该解决方案不起作用。

【问题讨论】：

标签： postgresql postgis


【解决方案1】：

不就是在做应该做的事吗？哪个是为了补偿由于将椭球投影到二维平面结构中造成的失真？我相信，你离赤道越远，你会看到越多的椭圆形缓冲区。

示例：

db=# SELECT ST_AsText(
     ST_Buffer(
        ST_GeomFromText('SRID=4326;POINT(43.29 5.41)'),0.001, 'quad_segs=16')
    );

此查询返回埃塞俄比亚东南部的一个圆圈：

POLYGON((43.291 5.41,43.2909951847267
5.40990198285967,43.2909807852804 5.40980490967798,43.2909569403357 5.40970971532275,43.2909238795325 5.40961731656764,43.2908819212644 5.40952860326317,43.2908314696123 5.40944442976698,43.2907730104534 5.40936560671584,43.2907071067812 5.40929289321881,43.2906343932842 5.40922698954664,43.290555570233 5.4091685303877,43.2904713967368 5.40911807873565,43.2903826834324 5.40907612046749,43.2902902846773 5.40904305966427,43.290195090322 5.4090192147196,43.2900980171403 5.40900481527333,43.29 5.409,43.2899019828597 5.40900481527333,43.289804909678 5.4090192147196,43.2897097153227 5.40904305966427,43.2896173165676 5.40907612046749,43.2895286032632 5.40911807873565,43.289444429767 5.4091685303877,43.2893656067158 5.40922698954664,43.2892928932188 5.40929289321881,43.2892269895466 5.40936560671584,43.2891685303877 5.40944442976698,43.2891180787356 5.40952860326317,43.2890761204675 5.40961731656764,43.2890430596643 5.40970971532275,43.2890192147196 5.40980490967798,43.2890048152733 5.40990198285967,43.289 5.41,43.2890048152733 5.41009801714033,43.2890192147196 5.41019509032202,43.2890430596643 5.41029028467725,43.2890761204675 5.41038268343237,43.2891180787356 5.41047139673683,43.2891685303877 5.41055557023302,43.2892269895466 5.41063439328416,43.2892928932188 5.41070710678119,43.2893656067158 5.41077301045336,43.289444429767 5.4108314696123,43.2895286032632 5.41088192126435,43.2896173165676 5.41092387953251,43.2897097153227 5.41095694033573,43.289804909678 5.4109807852804,43.2899019828597 5.41099518472667,43.29 5.411,43.2900980171403 5.41099518472667,43.290195090322 5.4109807852804,43.2902902846773 5.41095694033573,43.2903826834324 5.41092387953251,43.2904713967368 5.41088192126435,43.290555570233 5.4108314696123,43.2906343932842 5.41077301045336,43.2907071067812 5.41070710678119,43.2907730104534 5.41063439328416,43.2908314696123 5.41055557023302,43.2908819212644 5.41047139673683,43.2909238795325 5.41038268343237,43.2909569403357 5.41029028467725,43.2909807852804 5.41019509032202,43.2909951847267 5.41009801714033,43.291 5.41))

在离赤道稍远一点的突尼斯POINT(9.76 36.61)：

POLYGON((9.761 36.61,9.76099518472667 36.6099019828597,9.7609807852804 36.609804909678,9.76095694033573 36.6097097153227,9.76092387953251 36.6096173165676,9.76088192126435 36.6095286032632,9.7608314696123 36.609444429767,9.76077301045336 36.6093656067158,9.76070710678119 36.6092928932188,9.76063439328416 36.6092269895466,9.76055557023302 36.6091685303877,9.76047139673683 36.6091180787356,9.76038268343236 36.6090761204675,9.76029028467725 36.6090430596643,9.76019509032202 36.6090192147196,9.76009801714033 36.6090048152733,9.76 36.609,9.75990198285967 36.6090048152733,9.75980490967798 36.6090192147196,9.75970971532275 36.6090430596643,9.75961731656763 36.6090761204675,9.75952860326317 36.6091180787356,9.75944442976698 36.6091685303877,9.75936560671584 36.6092269895466,9.75929289321881 36.6092928932188,9.75922698954664 36.6093656067158,9.7591685303877 36.609444429767,9.75911807873565 36.6095286032632,9.75907612046749 36.6096173165676,9.75904305966427 36.6097097153227,9.7590192147196 36.609804909678,9.75900481527333 36.6099019828597,9.759 36.61,9.75900481527333 36.6100980171403,9.7590192147196 36.610195090322,9.75904305966427 36.6102902846773,9.75907612046749 36.6103826834324,9.75911807873565 36.6104713967368,9.7591685303877 36.610555570233,9.75922698954664 36.6106343932842,9.75929289321881 36.6107071067812,9.75936560671584 36.6107730104534,9.75944442976698 36.6108314696123,9.75952860326317 36.6108819212644,9.75961731656763 36.6109238795325,9.75970971532275 36.6109569403357,9.75980490967798 36.6109807852804,9.75990198285967 36.6109951847267,9.76 36.611,9.76009801714033 36.6109951847267,9.76019509032202 36.6109807852804,9.76029028467725 36.6109569403357,9.76038268343236 36.6109238795325,9.76047139673683 36.6108819212644,9.76055557023302 36.6108314696123,9.76063439328416 36.6107730104534,9.76070710678119 36.6107071067812,9.76077301045336 36.6106343932842,9.7608314696123 36.610555570233,9.76088192126435 36.6104713967368,9.76092387953251 36.6103826834324,9.76095694033573 36.6102902846773,9.7609807852804 36.610195090322,9.76099518472667 36.6100980171403,9.761 36.61))

而这个更远，在挪威北部POINT(23.20 69.94)：

POLYGON((23.201 69.94,23.2009951847267 69.9399019828597,23.2009807852804 69.939804909678,23.2009569403357 69.9397097153227,23.2009238795325 69.9396173165676,23.2008819212643 69.9395286032632,23.2008314696123 69.939444429767,23.2007730104534 69.9393656067158,23.2007071067812 69.9392928932188,23.2006343932842 69.9392269895466,23.200555570233 69.9391685303877,23.2004713967368 69.9391180787356,23.2003826834324 69.9390761204675,23.2002902846773 69.9390430596643,23.200195090322 69.9390192147196,23.2000980171403 69.9390048152733,23.2 69.939,23.1999019828597 69.9390048152733,23.199804909678 69.9390192147196,23.1997097153227 69.9390430596643,23.1996173165676 69.9390761204675,23.1995286032632 69.9391180787356,23.199444429767 69.9391685303877,23.1993656067158 69.9392269895466,23.1992928932188 69.9392928932188,23.1992269895466 69.9393656067158,23.1991685303877 69.939444429767,23.1991180787357 69.9395286032632,23.1990761204675 69.9396173165676,23.1990430596643 69.9397097153227,23.1990192147196 69.939804909678,23.1990048152733 69.9399019828597,23.199 69.94,23.1990048152733 69.9400980171403,23.1990192147196 69.940195090322,23.1990430596643 69.9402902846772,23.1990761204675 69.9403826834324,23.1991180787357 69.9404713967368,23.1991685303877 69.940555570233,23.1992269895466 69.9406343932842,23.1992928932188 69.9407071067812,23.1993656067158 69.9407730104534,23.199444429767 69.9408314696123,23.1995286032632 69.9408819212643,23.1996173165676 69.9409238795325,23.1997097153227 69.9409569403357,23.199804909678 69.9409807852804,23.1999019828597 69.9409951847267,23.2 69.941,23.2000980171403 69.9409951847267,23.200195090322 69.9409807852804,23.2002902846773 69.9409569403357,23.2003826834324 69.9409238795325,23.2004713967368 69.9408819212643,23.200555570233 69.9408314696123,23.2006343932842 69.9407730104534,23.2007071067812 69.9407071067812,23.2007730104534 69.9406343932842,23.2008314696123 69.940555570233,23.2008819212643 69.9404713967368,23.2009238795325 69.9403826834324,23.2009569403357 69.9402902846772,23.2009807852804 69.940195090322,23.2009951847267 69.9400980171403,23.201 69.94))

要使您的缓冲区忽略投影引起的失真，请考虑以下查询（意大利为POINT）：

SELECT 
  ST_Buffer(
    ST_GeomFromGeoJSON('{"type":"Point","coordinates":[11.26,44.42]}')::geography,
1000,'quad_segs=16')::geometry;

说明：

使用GEOMETRY 和GEOGRAPHY 的计算方式不同，结果也不同。 GEOGRAPHY 计算球面上的坐标（可能比GEOMETRY 慢得多）并使用meters 作为测量单位，而GEOMETRY 使用平面投影并使用SRS 单位。

注意：对于 OP 的用例，最后一个查询末尾的 GEOMETRY 转换是必要的，请参见下面的 cmets。

【讨论】：

  • 你有问题。离赤道越远，你的圆就越像椭圆。
  • 我只是想提出它，因为我相信这是一个很酷的功能。如果您真的想不考虑投影，请尝试使用geography 作为数据类型：SELECT ST_AsText( ST_Buffer(ST_GeomFromText('SRID=4326;POINT(23.20 69.94)')::GEOGRAPHY,1000, 'quad_segs=16') );
  • 我的几何列与特定的 SRID 无关，在将其打印到 OpenLayer 时，我必须使用 ST_AsEWKT 进行翻译。现在。我有另一列带有圆心的 GeoJSON。我试过这个类似于你的代码：UPDATE &lt;table&gt; SET geometry_column = ST_Buffer(ST_SetSRID(ST_GeomFromGeoJSON(geojson_column::TEXT),3857),1000,'quad_segs=16') WHERE id = 1234;没有SetSRID我得到一个椭圆。有了它，我在地图上什么也得不到。
  • 它在这里做你想要的吗？ SELECT ST_AsEWKT(ST_Buffer(ST_GeomFromText('POINT(23.20 69.94)')::GEOGRAPHY,1000,'quad_segs=16'));
  • 或者这个？ （您可以删除 SRID）UPDATE &lt;table&gt; SET geometry_column = ST_Buffer(ST_SetSRID(ST_GeomFromGeoJSON(geojson_column::TEXT),3857)::GEOGRAPHY,1000,'quad_segs=16') WHERE id = 1234;。考虑用一些示例数据创建一个小提琴，这样我们就知道你得到了什么:-)
【解决方案2】：

也许你可以试试这个，它是一个直径一公里的区域。我对其进行了测试，它对我有用：

SELECT ST_Buffer(  
    ST_MakePoint(-122.325959,47.625138)::geography, 
    1000)::geometry;

请参阅here 以获得更好的理解。 我没有测试它，但希望它会帮助你。

回顾一下 Abdullah Alger 在解决方案中所做的事情，您可以在上面的链接中看到：

首先，他有一个名为 stores 的数据库，其中包含经纬度列，没有包含 Starbuck 数据集的几何列。

然后他在查询中添加几何：

SELECT AddGeometryColumn('stores', 'geom', 4326, 'POINT', 2);

之后更新geom列

【讨论】：

  • 我能解释一下否决票吗？这将帮助我理解
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