Kalanand's December 2015 Log

December 1st

#include <iostream>
#include <numeric>
#include <vector>
#include <algorithm>

template <typename T>
void compute_mean_stdev(std::vector<T>& v, T& mean, T& stdev) { 

   mean = std::accumulate(v.begin(), v.end(), 0.0) / v.size();
   stdev = 0;
   std::for_each (v.begin(), v.end(), [&](const T x) {stdev += (x - m) * (x - m);});
   stdev = sqrt(stdev / (v.size()-1));
}

December 7th

        a = sin²(Δφ/2) + cosφ₁ . cosφ₂ . sin²(Δλ/2)
        distance = 2 . R . atan2(√a, √(1−a)),

where φ is latitude, λ longitude, R earth's radius (= 6371 km). Here is a quick stand alone code.

//geo_distance_calculator.h
#pragma once
#include <iostream>
#include <cmath>

template <typename T>
float geo_distance_km(const T& lon1, const T& lat1, const T& lon2, const T& lat2)
{
    const uint32_t R = 6371; // kilometers
    constexpr float deg_to_red = M_PI / 180;

    float phi1 = lat1 * deg_to_red;
    float phi2 = lat2 * deg_to_red;
    float dPhi = (lat2-lat1) * deg_to_red;
    float dLam = (lon2-lon1) * deg_to_red;

    float a = pow(sin(dPhi/2),2) + cos(phi1)*cos(phi2)*pow(sin(dLam/2),2);
    return 2 * R * atan2(sqrt(a), sqrt(1-a));
} 

Go to November's log