geodjango(postgis)中两个3D点之间的距离 [英] Distance between two 3D point in geodjango (postgis)

问题描述

我有以下问题:
我创建了两点，例如:

I have the following problem:
I created two points, for example:

SRID=3857;POINT Z (62780.8532226825 5415035.177460473 100)
SRID=3857;POINT Z (62785.8532226825 5415035.177460473 70)

如您所见，X坐标相差5m，Z坐标相差30m. 当我在django shell中运行a.distance(b)时，它返回 5 ，这是错误的.

As you can see, there is 5m difference in X coordinates, and 30m in Z coordinates. When I run a.distance(b) in django shell, it returns 5, which is wrong.

但是，当我在psql shell中运行时:

However, whenIi run in a psql shell:

SELECT ST_3DDistance(a.coordinates, b.coordinates)
FROM restapi_entityxyz a, restapi_entityxyz b
WHERE a.external_id='6841zef1561' AND b.external_id='1G23Fzd';

它返回:

st_3ddistance
------------------
 30.4138126514911

哪个是正确答案.

是geodjango中缺少功能还是错误?
我应该使用自定义库来执行这样的计算吗?

Is it a lack of functionality in geodjango or a bug?
Should I use a custom library to perform such a calculation?

我的环境如下:

• Python 3.5，
• Django，
• postgresql 9.4 + postgis
• gdal和许多python库.

推荐答案

django距离方法不是用于计算3D点(带有高程)的距离，而是用于计算2D.

The django distance method is not for calculating the distance of 3D points (with elevation) but of 2D.

我们可以通过创建自定义3d距离计算方法来解决此问题，例如此处所述: 使用纬度经度和海拔(海拔)

We can work around that by creating a custom 3d distance calculation method, like the one described here: Calculating distance between two points using latitude longitude and altitude (elevation)

• 让:
  polar_point_1 = (long_1, lat_1, alt_1)
  和
  polar_point_2 = (long_2, lat_2, alt_2)

• Let:
  polar_point_1 = (long_1, lat_1, alt_1)
  and
  polar_point_2 = (long_2, lat_2, alt_2)

利用此将每个点转换为等效的笛卡尔 公式:

Translate each point to it's Cartesian equivalent by utilizing this formula:

x = alt * cos(lat) * sin(long)
y = alt * sin(lat)
z = alt * cos(lat) * cos(long)

，您将分别获得p_1 = (x_1, y_1, z_1)和p_2 = (x_2, y_2, z_2)点.

最后使用欧几里得公式:

Finally use the Euclidean formula:

dist = sqrt((x_2-x_1)**2 + (y_2-y_1)**2 + (z_2-z_1)**2)

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在这里我回答的第二部分中确认了类似问题的解决方案:使用GeoDjango进行3d距离计算

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Confirmed solution of a similar issue from the second part of my answer here: 3d distance calculations with GeoDjango

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