api/middleware/search.js

function deg2rad(degrees) {
	return Math.PI*degrees/180;
}

function rad2deg(radians) {
	return 180.0*radians/Math.PI;
}

// Semi-axes of WGS-84 geoidal reference
var WGS84_a = 6378137.0;  // Major semiaxis [m]
var WGS84_b = 6356752.3;  // Minor semiaxis [m]

// Earth radius at a given latitude, according to the WGS-84 ellipsoid [m]
function WGS84EarthRadius(lat){
	// http://en.wikipedia.org/wiki/Earth_radius
    var An = WGS84_a*WGS84_a * Math.cos(lat);
    var Bn = WGS84_b*WGS84_b * Math.sin(lat);
    var Ad = WGS84_a * Math.cos(lat);
    var Bd = WGS84_b * Math.sin(lat);
    return Math.sqrt( (An*An + Bn*Bn)/(Ad*Ad + Bd*Bd) );
}
    
// Bounding box surrounding the point at given coordinates,
// assuming local approximation of Earth surface as a sphere
// of radius given by WGS84
function boundingBox(latitudeInDegrees, longitudeInDegrees, halfSideInKm) {
	var lat = deg2rad(latitudeInDegrees);
    var lon = deg2rad(longitudeInDegrees);
    var halfSide = 1000*halfSideInKm;

    // Radius of Earth at given latitude
    var radius = WGS84EarthRadius(lat);
    // Radius of the parallel at given latitude
    var pradius = radius*Math.cos(lat);

    var latMin = lat - halfSide/radius;
    var latMax = lat + halfSide/radius;
    var lonMin = lon - halfSide/pradius;
    var lonMax = lon + halfSide/pradius;

    return {
    	'bottom_left': {
    		'lat': rad2deg(latMin), 
    		'lon': rad2deg(lonMin)
    	},
    	'top_right': {
    		'lat': rad2deg(latMax), 
    		'lon': rad2deg(lonMax)	
    	} 
    };
}
    


// middleware
function middleware(req, res, next){
  req.clean = req.clean || {};
  // ideally, bbox should be part of the req (and not to be calculated)
  // TBD
  req.clean.bbox = boundingBox(req.query.lat, req.query.lon, 20);
  next();
}

// middleware
module.exports.middleware = middleware