Solved

Calculate Sun Position in Lat/Lon from Date/time

Posted on 2008-06-20
3
2,505 Views
Last Modified: 2010-05-18
I am developing an application that automates the 3D Globe control provided by ESRI.

ESRI use this globe themselves in there ArcGlobe application, and within this app it is possible to specify a date/time and plot the sun against the globe.

I wish to replicate this functionality in my application, however ESRI do not appear to have exposed this functionality in the API.

As far as I am aware it is only possible to set the sun position directly as a Lat/Lon

What I need is either :
a) a pointer to the ESRI API to get Sun Lat/Lon from Date/Time

or

b) code to derive the Sun Lat/Lon from Date/Time.

Note: I do not wish the Sun Azimuth/Altitute I have found these calculations many times. I wont the Lat/Lon position that the sun is directly above. As shown on this site : http://www.fourmilab.ch/cgi-bin/Earth

Thanks in Advance

G
0
Comment
Question by:Gordonp
  • 2
3 Comments
 
LVL 53

Accepted Solution

by:
Infinity08 earned 500 total points
ID: 21829728
I've quickly written the following code. I assume that's what you intended ? The precision is relatively good (using Spencer's algorithm), but could be better with more accurate formula's (like Michalsky's almanac algorithm for example, from his "The Astronomical Almanac's algorithm for approximate solar position" paper).
#include <stdio.h>
#include <time.h>
#include <math.h>
 
#define PI 3.14159265358979323846
 
double solar_declination(struct tm *t) {
  /* day angle : */
  double J = 1.0 + ((double) t->tm_yday);
  double tau_d = 2.0 * PI * (J - 1.0) / 365.0;
  
  /* solar declination */
  double delta_s = 0.006981 - 0.399912 * cos(      tau_d) + 0.070257 * sin(      tau_d)
                            - 0.006758 * cos(2.0 * tau_d) + 0.000907 * sin(2.0 * tau_d)
                            - 0.002697 * cos(3.0 * tau_d) + 0.001480 * sin(3.0 * tau_d);
 
  return delta_s;
}
 
int main(void) {
  time_t now = time(0);
  struct tm *now_tm = gmtime(&now);
  double hour = now_tm->tm_hour + (now_tm->tm_min / 60.0) + (now_tm->tm_sec / 3600.0);
 
  double latitude = solar_declination(now_tm);
  double longitude = PI - (2.0 * PI * hour / 24.0);
  
  fprintf(stdout, "latitude  : %10.5f radians (%10.5f degrees)\n", latitude, latitude * 180.0 / PI);
  fprintf(stdout, "longitude : %10.5f radians (%10.5f degrees)\n", longitude, longitude * 180.0 / PI);
 
  return 0;
}

Open in new window

0
 
LVL 3

Author Comment

by:Gordonp
ID: 21829780
This appears to be exactly what I'm after. Just need to check it out, and I'll be back to Accept if formally.
0
 
LVL 3

Author Closing Comment

by:Gordonp
ID: 31469075
Thanks for your help
0

Featured Post

Announcing the Most Valuable Experts of 2016

MVEs are more concerned with the satisfaction of those they help than with the considerable points they can earn. They are the types of people you feel privileged to call colleagues. Join us in honoring this amazing group of Experts.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Math Question 1 104
Arduino EDI - Programming language 3 103
Math Equation 23 105
What is sqrt( (x+b/2a)^2) 35 75
Lithium-ion batteries area cornerstone of today's portable electronic devices, and even though they are relied upon heavily, their chemistry and origin are not of common knowledge. This article is about a device on which every smartphone, laptop, an…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
This tutorial demonstrates how to identify and create boundary or building outlines in Google Maps. In this example, I outline the boundaries of an enclosed skatepark within a community park.  Login to your Google Account, then  Google for "Google M…
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.

766 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question