Calculating bounding box a certain distance away from a lat/long coordinate in Java

I wrote an article about finding the bounding coordinates:

http://JanMatuschek.de/LatitudeLongitudeBoundingCoordinates

The article explains the formulae and also provides a Java implementation. (It also shows why IronMan's formula for the min/max longitude is inaccurate.)

double R = 6371;  // earth radius in km

double radius = 50; // km

double x1 = lon - Math.toDegrees(radius/R/Math.cos(Math.toRadians(lat)));

double x2 = lon + Math.toDegrees(radius/R/Math.cos(Math.toRadians(lat)));

double y1 = lat + Math.toDegrees(radius/R);

double y2 = lat - Math.toDegrees(radius/R);

Although I would also recommend JTS.

import com.vividsolutions.jts.geom.Envelope;

...
Envelope env = new Envelope(centerPoint.getCoordinate());
env.expandBy(distance_in_degrees); 
...

Now env contains your envelope. It's not actually a "square" (whatever that means on the surface of a sphere), but it should do.

You should note that the distance in degrees will depend on the latitude of the center point. At the equator, 1 degree of latitude is about 111km, but in New York, it's only about 75km.

The really cool thing is that you can toss all your points into a com.vividsolutions.jts.index.strtree.STRtree and then use it to quickly calculate points inside that Envelope.