request for function: construct LatLngBounds from LatLng and radius

[fearless_fool]

I haven't found a straightforward way to construct a LatLngBounds given a center point and a radius.  The best approaches I've seen are described in http://www.movable-type.co.uk/scripts/latlong.html, but it seems odd that I'd need to put that much trig code in my own javascript code -- it ought to be a library function.

If there is such such a built-in function, I haven't found it.  If there isn't, I'd like to see it added.

[Andrew Leach]

On 30 January 2012 17:41, fearless_fool <rdp...@gmail.com> wrote:
> I haven't found a straightforward way to construct a LatLngBounds given a
> center point and a radius.  The best approaches I've seen are described
> in http://www.movable-type.co.uk/scripts/latlong.html, but it seems odd that
> I'd need to put that much trig code in my own javascript code -- it ought to
> be a library function.

Geometry library
http://code.google.com/apis/maps/documentation/javascript/geometry.html#Distance

"Given a particular heading, an origin location, and the distance to
travel (in meters), you can calculate the destination coordinates
using computeOffset()."

You can construct a LatLngBounds by using four calls to computeOffset().

[Rossko]

> If there is such such a built-in function, I haven't found it.  If there
> isn't, I'd like to see it added.

Isn't it Circle() ?http://code.google.com/apis/maps/documentation/
javascript/overlays.html#Circles
which has a getBounds() method
http://code.google.com/apis/maps/documentation/javascript/reference.html#Circle

[fearless_fool]

@Rossko:

Yes, it appears that something like:

function convertToBounds(latLng, radius) {
  return new google.maps.Circle({center: latLng, radius: radius}).getBounds();
}

... should do the trick. Thank you!

[DiTieM]

It took time to find that function to me (I dont remember the source). It could certainly be added to the API set.

function llr_to_bounds ( lat, lng, distance )

{

  // angular distance in radians on a great circle

  var radius  = 6371000

    , radDist = distance / radius

    , radLat  = to_rad( lat )

    , radLon  = to_rad( lng )

    , minLat  = radLat - radDist

    , maxLat  = radLat + radDist

    , minLon

    , maxLon

    , MIN_LAT = -Math.PI/2

    , MAX_LAT =  Math.PI/2

    , MIN_LON = -Math.PI

    , MAX_LON =  Math.PI   ;

  if ( minLat > MIN_LAT && maxLat < MAX_LAT )

    {

       var deltaLon = Math.asin( Math.sin( radDist ) / Math.cos( radLat ) ) ;

        

       minLon = radLon - deltaLon;

       maxLon = radLon + deltaLon;

       if ( minLon < MIN_LON ) minLon += 2 * Math.PI ;

       if ( maxLon > MAX_LON ) maxLon -= 2 * Math.PI ;

    } 

  else

    {

// a pole is within the distance

minLat = Math.max( minLat, MIN_LAT ) ;

maxLat = Math.min( maxLat, MAX_LAT ) ;

minLon = MIN_LON ;

maxLon = MAX_LON ;

    }

  return new google.maps.LatLngBounds( new google.maps.LatLng( to_deg( minLat ), to_deg( minLon ) )

                                     , new google.maps.LatLng( to_deg( maxLat ), to_deg( maxLon ) ) ) ;

}

[Rossko]

> It took time to find that function to me (I dont remember the source). It
> could certainly be added to the API set.

Why? Circle() exists already and has a getBounds() method
Is there a problem with that? (might not work well at the poles for
example, not much does in Mercator)

[JKurtock]

Remember that everything added to an API set makes the API larger,
slower, harder to load, etc. If only 1% of users want to use a
function, and it's a matter of 20 lines of javascript for those users
to add it themselves, why would you want to burden the other 99%?

The development team does (I think) a very good job of adding that
which is truly useful, and leaving out the "nice-to-haves." So don't
feel bad if your pet function is not picked up.

- Jeff

[DiTieM]

hmmm Rosko, now I understood your post. Need to check that function! 

But looks like the correct answer, hence there is absolutely no need for 

the function I posted!

Sorry for the mess