3d distance calculations with GeoDjango

Question

I am using

• python 2.7.12
• django 1.10.6
• postgreSQL 9.5.6
• postGIS 2.2.2

First question

I ne

Answer 1

Let's break the problem down:

1. In the Distance class documentation, we can read the following:

   Accepts two geographic fields or expressions and returns the distance between them, as a Distance object.

   So the Distance(p1, p2) returns a Distance object.
   If you do:

   p1 = Instrument.objects.get(pk=151071000).coordinates
   p2 = Instrument.objects.get(pk=151071008).coordinates
   d = Distance(m=p1.distance(p2))
   print d.m
   

   You will get the measurement in meters.
   

   I would stick with the annotate solution, which seems more solid! (opinionated response)

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2. Distance calculates the 2D distance between two points. In order to get a 3D calculation, you need to create one yourself.
   You can have a look at my method from this question: Calculating distance between two points using latitude longitude and altitude (elevation)

   EDIT 2019: Since the initial answer I have composed a Q&A style example here: How to calculate 3D distance (including altitude) between two points in GeoDjango that uses a far better (and less calculation error-prone) distance calculation between 2 points with altitude.

   In sort:

   We need to calculate the 2D great-circle distance between 2 points using either the Haversine formula or the Vicenty formula and then we can combine it with the difference (delta) in altitude between the 2 points to calculate the Euclidean distance between them as follows:

   dist = sqrt(great_circle((lat_1, lon_1), (lat-2, lon_2).m**2, (alt_1 - alt_2)**2)
   

   The solution assumes that the altitude is in meters and thus converts the great_circle's result into meters as well.

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Leaving this here for comment continuation purposes.

2. Distance calculates the 2D distance between two points. In order to get a 3D calculation, you need to create one yourself.
You can have a look at my method from this question: Calculating distance between two points using latitude longitude and altitude (elevation)

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

• 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)
  

  and you will have p_1 = (x_1, y_1, z_1) and p_2 = (x_2, y_2, z_2) points respectively.

• Finally use the Euclidean formula:

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