Geodjango：如何从点缓冲 [英] Geodjango: How to Buffer From Point

问题描述

我想进行基于半径的距离搜索。为此，我想在一个点对象周围创建一个缓冲区，以过滤其中的对象。

这是我要使用的位置：

 >> lat = 37.7762179974 
>> lon = -122.411562492 
>>从django.contrib.gis.geos导入Point 
>> pnt =点（纬度，经度）
>> buf = pnt.buffer（0.0001）
  

但是我在过滤时遇到问题事物基于它们是否在缓冲区内：

 >> z = Thing.objects.filter（pnt__intersects = buf）
  

（我知道上面的是不正确的，但是我用它来阐述我要做什么。）

如何在周围创建缓冲区指向，然后过滤缓冲区内部的事物？

---

编辑： models.py

  class Thing（models.Model）：
 lat = models.FloatField（）
 lon = models.FloatField（）
  

如何根据由这两个模型字段组合而成的点进行过滤？

这显然不起作用，因为我的模型中没有 pnt 字段：

 >> pnt =点（纬度，经度）
>> z = Thing.objects.filter（pnt__intersects = buf）
  

但是我该怎么做？ / p>

解决方案

PostGIS的方法称为 ST_MakePoint 可以创建2D，3D或4D点。

在一个上一个答案，我们看到的是可以从现有的PostGIS函数创建自定义数据库函数：

  from django.contrib.gis.db.models.functions import GeoFunc 
 
 class MakePoint（GeoFunc）：
 function ='ST_MakePoint'
  

现在，我们可以通过 annotate（） ing 并在其上应用相交：

  z = Thing.objects。注释（pnt = MakePoint（'lat'，'lon'））
 .filter（pnt__intersects = buf）
  

您可以通过使用 GeoFunc（） 和 F（） 表达式：

<来自django.contrib.gis.db.models.functions的pre> import GeoFunc

z = Thing.objects.annotate（pnt = GeoFunc（
F（ 'lat'），F（'lon'），
function ='ST_MakePoint'
）.filter（pnt__intersects = buf）


---

注意：您可以考虑添加 pnt 在您的事物模型中，请避免上述情况。

I want to have a radius based distance search. To do this, I want to create a buffer around a point object in order to filter objects that are inside it.

Here is where I am at with it:

>>> lat = 37.7762179974
>>> lon = -122.411562492
>>> from django.contrib.gis.geos import Point
>>> pnt = Point(lat, lon)
>>> buf = pnt.buffer(0.0001)

But I am having problems filtering the Thing objects based on whether they are inside the buffer:

>>> z = Thing.objects.filter(pnt__intersects=buf) 

(I know that the above is incorrect, but I use it to elaborate what I am trying to do.)

How can I create a buffer around the Point and then filter Things that are inside the buffer?

---

EDIT: models.py

class Thing(models.Model):
    lat = models.FloatField()
    lon = models.FloatField()

How can I filter based on a point comprised of a combination of these two model fields?
This cannot work obviously, because I do not have a pnt field in my model:

>>> pnt = Point(lat, lon)
>>> z = Thing.objects.filter(pnt__intersects=buf) 

But how can I do something similar?

解决方案

PostGIS has a method called ST_MakePoint which can create a 2D, 3D or 4D point.

In a previous answer we saw that it is possible to create a custom database function from an existing PostGIS function:

from django.contrib.gis.db.models.functions import GeoFunc

class MakePoint(GeoFunc):
    function='ST_MakePoint'

Now we can create a point by annotate()ing and apply the intersects on it:

z = Thing.objects.annotate(pnt=MakePoint('lat', 'lon'))
                 .filter(pnt__intersects=buf)

You can achieve the same effect by utilizing GeoFunc() and F() expressions:

from django.contrib.gis.db.models.functions import GeoFunc

z = Thing.objects.annotate(pnt=GeoFunc(
        F('lat'), F('lon'),
        function='ST_MakePoint'
    ).filter(pnt__intersects=buf)

---

Note: You could consider adding a pnt field in your Thing model and avoid the above.

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