使用django.contrib.gis.measure.D时的GeoDjango dwithin错误 [英] GeoDjango dwithin errors when using django.contrib.gis.measure.D

问题描述

首先:RHEL 6.5上的Python 2.7.6，Django 1.6.5，Postgres 9.3.4，PostGIS 2.1.3，psycopg2 2.5.3

First off: Python 2.7.6, Django 1.6.5, Postgres 9.3.4, PostGIS 2.1.3, psycopg2 2.5.3 on RHEL 6.5

以下是相关模型:

class Location(models.Model):
    name = models.CharField(max_length=255)
    geometry = models.MultiPolygonField(blank=True, default=None, null=True)
    objects = models.GeoManager()  # override the default manager with a GeoManager instance
    parent = models.ForeignKey('self', blank=True, default=None, null=True)

    def __unicode__(self):
        return self.name

此查询应根据文档:

touching_locations = Location.objects.filter(geometry__dwithin=(location.geometry, D(km=5)))
logging.debug(type(touching_locations))
logging.debug(len(touching_locations))

但事实并非如此.第一个调试调用有效，但是第二个调试调用抛出ValueError:

But it doesn't. The first debug call works, but the second throws a ValueError:

<class 'django.contrib.gis.db.models.query.GeoQuerySet'>
ValueError: Only numeric values of degree units are allowed on geographic DWithin queries.

如果我通过将D(km=5)更改为5进行了小的更改:

If I make a small change by changing D(km=5) to 5:

touching_locations = Location.objects.filter(geometry__dwithin=(location.geometry, 5))
logging.debug(type(touching_locations))
logging.debug(len(touching_locations))

突然间它起作用了.我得到的输出是这样的:

All of a sudden it works. The output I get is this:

<class 'django.contrib.gis.db.models.query.GeoQuerySet'>
54

有人知道为什么这没有按预期进行吗?这可能是一个错误，还是我犯了一个我看不见的错误?

Does anyone know why this isn't working as expected? Is this perhaps a bug, or am I making a mistake I just don't see?

我认为这可能是Django错误.我继续在此处打开了一张票.确定正确的解决方法后，我将在此处添加答案.

[edit]
I think this may be a Django bug. I went ahead and opened a ticket here. Once I figure out what the proper fix is, I'll add the answer here.

推荐答案

我收到了我提交的票证的回复(

I got a response to the ticket I submitted (https://code.djangoproject.com/ticket/22830). Apparently, I found a seemingly undocumented (or at least not clearly documented) problem that dwithin queries have with Distance objects. A dev says this:

由于您的对象位于地理坐标中(默认为几何字段 到WGS84)，则必须以度单位提供距离.这是 例如匹配PostGIS定义:

As your objects are in geographic coordinates (geometry fields default to WGS84), you have to provide the distance as degree units. This is for example matching the PostGIS definition:

布尔值ST_DWithin(几何g1，几何g2，双精度 distance_of_srid);

boolean ST_DWithin(geometry g1, geometry g2, double precision distance_of_srid);

distance_of_srid是WGS84的度数.所以这5个适合您的 示例表示5度，而不是5公里！

distance_of_srid being degrees for WGS84. So the 5 that works in your example means 5 degrees, not 5 km!

似乎他们将澄清文档以使其更清楚(非常好！).

It looks like they're going to clarify the documentation to make this clearer (great!).

因为我想要的是5km，所以我需要将5km转换为度. 1度是大约111.325km.因此，1km = 1/111.325度.因此5km约为0.0449或约0.05度.因此，我只需要将此呼叫更改为:

Since what I want is 5km, I need to convert 5km to degrees. 1 degree is approximately 111.325km. Therefore, 1km = 1/111.325 degrees. 5km is therefore approximately 0.0449 or about 0.05 degrees. So I just need to change my call to this:

touching_locations = Location.objects.filter(geometry__dwithin=(location.geometry, 0.05))

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