Convert lat,long to bbox using WGS-84

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11-21-2018 09:39 AM
rajujee
New Contributor II

I am stuck how to convert lat,long to bbox using WGS-84. Is there a formula or function code you could share.

e.g. lon=-79.80617638166511

lat=43.17565342984143

bbox?


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RobertScheitlin__GISP
MVP Esteemed Contributor

Raju,

   My code snippet above is for a map click function where the event object passed is the map click event.

Here is a function to convert a lat lon to an extent.

function onSelDrawEnd(lat, lon) {
  var mapPnt = new Point(parseFloat(lon), parseFloat(lat));
  var scrPnt = map.toScreen(mapPnt);
  //Expand the point by 5 pixels
  var xMin = scrPnt .x - 2.5; //value in pixels
  var yMin = scrPnt .y - 2.5; //value in pixels
  var xMax = scrPnt .x + 2.5; //value in pixels
  var yMax = scrPnt .y + 2.5; //value in pixels
  var mp1 = map.toMap(new Point(xMin, yMin));
  var mp2 = map.toMap(new Point(xMax, yMax));
  var ext = new Extent(mp1.x, mp1.y, mp2.x, mp2.y, new SpatialReference({ wkid:4326 }));
  return Polygon.fromExtent(ext);
}‍‍‍‍‍‍‍‍‍‍‍‍‍

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RobertScheitlin__GISP
MVP Esteemed Contributor

Raju,


  To get a bounding box from a single point you just need to do some math to add and subtract for that point to get the minx, miny, maxx and maxy for the extent class constructor.

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rajujee
New Contributor II

Thanks Rob for always being helpful. I am using simple math to get bbox from lat,long. It is not accurate for closest zoom scale.

  var minxx = lon - 0.08999;
                  var maxxx = lon + 0.08999;
                  var minyy = lat - 0.08999;
                  var maxyy = lat - 0.08999;
           

 

                  console.log("weblink/bbox?" + "xmin=" + minxx + "&ymin=" + minyy + "&xmax=" + maxxx + "&ymax=" + maxyy).

I have WGS-84 projection. Do I have to add condition for each scale. e.g.

If (scale =11)

  var minxx = lon - 0.08999;
                  var maxxx = lon + 0.08999;
                  var minyy = lat - 0.08999;
                  var maxyy = lat - 0.08999;

elseif  (scale =19)

  var minxx = lon - ??;
                  var maxxx = lon + ??;
                  var minyy = lat - ??;
                  var maxyy = lat - ??;

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RobertScheitlin__GISP
MVP Esteemed Contributor

Raju,

  Normally I would be adding/subtracting values with a set number of pixels using toScreen and toMap.

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rajujee
New Contributor II

Thanks Rob for your response. Could you kindly provide an example for set of pixels toScreen and toMap. I have a deadline to meet.

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RobertScheitlin__GISP
MVP Esteemed Contributor

You working in 3.x or 4.x?

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rajujee
New Contributor II

I am using 3.x. Thanks in advance for your help!

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RobertScheitlin__GISP
MVP Esteemed Contributor

Raju,

  Here is how I turn a point into a polygon to query by:

    function onSelDrawEnd(event) {
      var geom = event.mapPoint;
      //Expand the point by 5 pixels
      var xMin = event.screenPoint.x - 2.5; //value in pixels
      var yMin = event.screenPoint.y - 2.5; //value in pixels
      var xMax = event.screenPoint.x + 2.5; //value in pixels
      var yMax = event.screenPoint.y + 2.5; //value in pixels
      var mp1 = map.toMap(new Point(xMin, yMin));
      var mp2 = map.toMap(new Point(xMax, yMax));
      var ext = new Extent(mp1.x, mp1.y, mp2.x, mp2.y, geom.spatialReference);
      var pPoly = Polygon.fromExtent(ext);
      queryFeaturesGraphical(pPoly);
    }
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rajujee
New Contributor II

Thanks Robert for sharing "turn point into a polygon".  Could you please guide how I can pass 'event' into my existing code (above code). Your help is appreciated.

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RobertScheitlin__GISP
MVP Esteemed Contributor

Raju,

   My code snippet above is for a map click function where the event object passed is the map click event.

Here is a function to convert a lat lon to an extent.

function onSelDrawEnd(lat, lon) {
  var mapPnt = new Point(parseFloat(lon), parseFloat(lat));
  var scrPnt = map.toScreen(mapPnt);
  //Expand the point by 5 pixels
  var xMin = scrPnt .x - 2.5; //value in pixels
  var yMin = scrPnt .y - 2.5; //value in pixels
  var xMax = scrPnt .x + 2.5; //value in pixels
  var yMax = scrPnt .y + 2.5; //value in pixels
  var mp1 = map.toMap(new Point(xMin, yMin));
  var mp2 = map.toMap(new Point(xMax, yMax));
  var ext = new Extent(mp1.x, mp1.y, mp2.x, mp2.y, new SpatialReference({ wkid:4326 }));
  return Polygon.fromExtent(ext);
}‍‍‍‍‍‍‍‍‍‍‍‍‍
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