I have this working now. Basically, I had to scrap the formula that I found in favor of another. The formula I was using was from .
The new function for finding initial heading, if anyone is interested, follows. It accepts latitudes and longitudes in degrees. Since decent formulas of this kind are apparently hard to find, I used the one that was implemented in javascript at http://www.csgnetwork.com/aviationbrgrngcalc.html. Thanks again for all the ideas. Here's the script: // Calculate initial heading function Initial_Hdg($lat1, $lon1, $lat2, $lon2) { // Convert latitudes to radians $lat1 = $lat1 * (2*M_PI)/360; $lat2 = $lat2 * (2*M_PI)/360; // Find angle between longitudes $deg_lon = $lon2 - $lon1; if ($deg_lon > 180) { $deg_lon = $deg_lon - 360; } if ($deg_lon< -180) { $deg_lon = 360 + $deg_lon; } // Convert longitude angle to radians $rad_lon = $deg_lon * (2*M_PI)/360; // Calculate Course $tcourse = sin($rad_lon) / ((cos($lat1)*tan($lat2)) - (sin($lat1)*cos($rad_lon))); $course = atan($tcourse); // Convert course to degrees $course = $course * 360 / (2*M_PI); // Check to see if any corrections are needed to the course if ($deg_lon == 0 && $lat1 > $lat2) { $course = 180; } if ($deg_lon< 0 && $course< 0) { $course = $course + 360; } else { if (($deg_lon< 0 && $course > 0) || ($deg_lon > 0 && $course< 0)) { $course = $course + 180; } } return $course; } -JS ------------------------ Yahoo! Groups Sponsor --------------------~--> Get Bzzzy! (real tools to help you find a job). Welcome to the Sweet Life. http://us.click.yahoo.com/A77XvD/vlQLAA/TtwFAA/HKFolB/TM --------------------------------------------------------------------~-> Community email addresses: Post message: [email protected] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED] Shortcut URL to this page: http://groups.yahoo.com/group/php-list Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/php-list/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
