Solved

Calculate Sun Position in Lat/Lon from Date/time

Posted on 2008-06-20
3
2,520 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

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

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

Suggested Solutions

Title # Comments Views Activity
C++ mouse_event mouse look 7 112
Embarcadero C++ Builder XE10.1 Berlin red arrow Indicator 2 75
Meaning of e^x sin(x) 2 50
boost::uuid crashes 17 41
Have you ever thought of installing a power system that generates solar electricity to power your house? Some may say yes, while others may tell me no. But have you noticed that people around you are now considering installing such systems in their …
This article seeks to propel the full implementation of geothermal power plants in Mexico as a renewable energy source.
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…

730 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