topic Re: Converting coordinates in ArcObjects SDK Questions

Converting coordinates

GeorgeFaraj — Mon, 24 Sep 2012 21:02:11 GMT

I am listening to the OnMouseDown event of my IMapControl4, and the IMapControlEvents2_OnMouseDownEvent provides a mapX and mapY. How do I convert this coordinate to WGS84? I need to interface with another 3rd party library that requires WGS84 coordinates as its input.

Thanks,
George Faraj

Re: Converting coordinates

NeilClemmons — Tue, 25 Sep 2012 12:46:48 GMT

You need to project the data to that coordinate system. The map x, y passed into the event are in whatever coordinate system the map is in, so just create a new point object, give it the same spatial reference as the map and set the x, y properties. Then call Project and pass in the spatial reference you want to project it to. You can get this spatial reference object from ISpatialReferenceFactory.CreateGeographicCoordinateSystem. After calling Project, the x, y properties will have the updated coordinates.

Re: Converting coordinates

GeorgeFaraj — Sun, 12 Dec 2021 04:08:50 GMT

Thank you Neil. That helped. I wrote the following method:

public static IPoint GetLatLngPointsFromMapPoints(this IActiveView view, IMapControl4 map, double controlX, double controlY)
{
 var mapPoint = new PointClass();
 mapPoint.SpatialReference = map.SpatialReference;
 mapPoint.PutCoords(controlX, controlY);

 if (mapPoint.SpatialReference.Name == "Unknown")
 {
  mapPoint.SpatialReference = view.ScreenDisplay.DisplayTransformation.ToMapPoint(0, 0).SpatialReference;
 }
 if (double.IsNaN(mapPoint.Z))
 {
  mapPoint.Z = 0;
 }

 if (mapPoint.SpatialReference.Name == "Unknown")
 {
  return null;
 }

 var spatialRefFactory = new SpatialReferenceEnvironment();
 var geoCoordSystem = spatialRefFactory.CreateGeographicCoordinateSystem((int)esriSRGeoCSType.esriSRGeoCS_WGS1984);
 mapPoint.Project(geoCoordSystem);
 return mapPoint;
}

And I'm getting values like -122.545187727749 and 45.6971389559235. Not sure if these are degrees or if they are just incorrect. Does this sound right to you?

Re: Converting coordinates

NeilClemmons — Tue, 25 Sep 2012 18:20:49 GMT

Without knowing what your original coordinate system and coordinates are I can't tell you if those values are correct or not. The results you're getting will be in decimal degrees since you are projecting into a geographic coordinate system. Remember that when expressed as x, y coordinates of a point that x = longitude and y = latitude. Longitude values range from 0 to 180 with positive values being measured East and negative values being measured West. Latitude values range from 0 to 90 with positive values being measured North and negative values being measured South. The coordinates you posted are near Vancouver, Canada.

Re: Converting coordinates

GeorgeFaraj — Tue, 25 Sep 2012 18:31:40 GMT

Alright, so I think I have the correct coordinates in degrees now. Thanks a lot!

Re: Converting coordinates

ΣταυρούλαΓιαννακοπούλου — Wed, 09 Dec 2020 11:32:43 GMT

Good morning everyone! I would like to ask if there is a way to define my coordinates, taking into account that I don't know their coordinates system. Is there a way to determine it? All I have is an xls file. Thank you very much for your collaboration!