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POGeo Spacial Bounding Box Rectangle Calculation Error: Latitude Incorrect
 

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  1. POGeo Spacial Bounding Box Rectangle Calculation Error: Latitude Incorrect
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    <p>Can any trig or GPS experts help me out here? I'm trying to create a geo-spacial bounding box (rectangle) calculation returning the maximum latitude and longitude using the following method that I've retrieved. I am calling the method once for each of the for bearings: north, south, east and west. With these four values I intend to query my Core Data store for all objects within the box.</p> <pre><code> -(CLLocation*) offsetLocation:(CLLocation*)startLocation:(double)offsetMeters:(double)bearing { double EARTH_MEAN_RADIUS_METERS = 6372796.99; double newLatitude = asin( sin(startLocation.coordinate.latitude) * cos(offsetMeters/EARTH_MEAN_RADIUS_METERS) + cos(startLocation.coordinate.latitude) * sin(offsetMeters/EARTH_MEAN_RADIUS_METERS) * cos(bearing) ); double newLongitude = startLocation.coordinate.longitude + atan2( sin(bearing) * sin(offsetMeters/EARTH_MEAN_RADIUS_METERS) * cos(startLocation.coordinate.latitude), cos(offsetMeters/EARTH_MEAN_RADIUS_METERS) - sin(startLocation.coordinate.latitude) * sin(newLatitude)); CLLocation *tempLocation = [[CLLocation alloc] initWithLatitude:newLatitude longitude:newLongitude]; [tempLocation autorelease]; return tempLocation; } </code></pre> <p>The problem is the calculation for the newLatitude offset is definitely incorrect. Given the following:</p> <p>startLocation: latitude 37.331688999999997, longitude -122.030731 offsetMeters : 1000 bearing : 0 (north)</p> <p>newLatitude returns -0.36726592610659514 (incorrect).</p> <p>Any suggestions? I've coded around this particular formula until now and this one has me stumped. I've also tried translating a different formula from PHP to no avail. I figure the above is exactly what I need if it can be tweaked.</p> <p>Thanks, b.dot </p>
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