Question

我想计算C中特定位置（纬度，经度）的日落。

我以http://edwilliams.org/sunrise_sunset_algorithm.htm

为模型

对于给定的模型，我尝试计算日出-这个值很好。我仍然得到日落的错误值：-11：-22。

以下是一些代码：

#include <stdio.h>
#include <math.h>
#define PI 3.1415926
#define ZENITH -.83

float calculateSunset(int year,int month,int day,float lat, float lng,int localOffset) {

//1. first calculate the day of the year
float N1 = floor(275 * month / 9);
float N2 = floor((month + 9) / 12);
float N3 = (1 + floor((year - 4 * floor(year / 4) + 2) / 3));
float N = N1 - (N2 * N3) + day - 30;

//2. convert the longitude to hour value and calculate an approximate time  
float lngHour = lng / 15;
float t = N + ((18 - lngHour) / 24);   //if setting time is desired:

//3. calculate the Sun's mean anomaly   
float M = (0.9856 * t) - 3.289;

//4. calculate the Sun's true longitude
float L = fmod(M + (1.916 * sin((PI/180)*M)) + (0.020 * sin(2 *(PI/180) * M)) + 282.634,360.0);

//5a. calculate the Sun's right ascension      
float RA = fmod(180/PI*atan(0.91764 * tan((PI/180)*L)),360.0);

//5b. right ascension value needs to be in the same quadrant as L   
float Lquadrant  = floor( L/90) * 90;
float RAquadrant = floor(RA/90) * 90;
RA = RA + (Lquadrant - RAquadrant);

//5c. right ascension value needs to be converted into hours   
RA = RA / 15;

//6. calculate the Sun's declination
float sinDec = 0.39782 * sin((PI/180)*L);
float cosDec = cos(asin(sinDec));

//7a. calculate the Sun's local hour angle
float cosH = (sin((PI/180)*ZENITH) - (sinDec * sin((PI/180)*lat))) / (cosDec * cos((PI/180)*lat));

if (cosH >  1) {
    printf("the sun never rises on this location (on the specified date)");
    return 0;
}

if (cosH < -1) {
    printf("the sun never sets on this location (on the specified date)");
    return 0;
}

//7b. finish calculating H and convert into hours
float H = acos(cosH); //   if setting time is desired:      
H = H / 15;

//8. calculate local mean time of rising/setting      
float T = H + RA - (0.06571 * t) - 6.622;

//9. adjust back to UTC
float UT = fmod(T - lngHour,24.0);

//10. convert UT value to local time zone of latitude/longitude
return UT + localOffset;

}

void printSunset() {

    float localT = calculateSunset(2018,10,4,51.8446,19.2094,2);
    double hours;
    float minutes = modf(localT,&hours)*60;
    printf("Sunset: ");
    printf("%.0f:%.0f",hours,minutes);   
    printf("\n"); 
}


int main()
{
  printSunset();
  return 0;
}

有人可以帮助我吗？我在做什么错了？

Answer 1

我认为您的主要问题是您希望fmod返回正结果-这是不正确的，fmod会保留正负号，即如果您将fmod取负值，则将得到一个（正确的）负结果，如果您将其用于正值（正确）的结果将为正。如果您需要一个正数结果，例如，如果结果为负数，则只需添加除数即可。

float a = fmod(T, 360.0);
if(a < 0) { a = a + 360.0; }

C语言的日落

1 个答案: