GPS-Logger/models.py

import math
from django.db import models
from django.contrib.gis.db.models.fields import PointField
from django.contrib.gis.db.models.functions import Distance
from django.contrib.gis.measure import D

class Marker(models.Model):
  timestamp = models.DateTimeField(unique=True)
  location = PointField(dim=2)
  alt = models.FloatField("Altitude")
  hdop = models.IntegerField(null=True, blank=True)
  speed = models.FloatField("Speed in km/h", null=True, blank=True)

class Trip(models.Model):
  startTime = models.DateTimeField()
  endTime = models.DateTimeField()
  name = models.CharField(max_length=255)
  description = models.TextField(null=True, blank=True)

class CensoredLocation(models.Model):
  location = PointField(dim=2)
  radius = models.IntegerField(default=800)
  name = models.CharField(max_length=255)

  def delete_markers(self) -> int:
    matches = Marker.objects.filter(location__distance_lt=(
      self.location,
      distance_to_decimal_degrees(D(m=self.radius), self.location.y)
    ))
    count = len(matches)
    matches.delete()
    return count


def distance_to_decimal_degrees(distance, latitude):
    """
    Source of formulae information:
        1. https://en.wikipedia.org/wiki/Decimal_degrees
        2. http://www.movable-type.co.uk/scripts/latlong.html
    :param distance: an instance of `from django.contrib.gis.measure.Distance`
    :param latitude: y - coordinate of a point/location
    """
    lat_radians = latitude * (math.pi / 180)
    # 1 longitudinal degree at the equator equal 111,319.5m equiv to 111.32km
    return distance.m / (111_319.5 * math.cos(lat_radians))