topic Re: How to convert screen pixels to map units in ArcGIS Pro SDK Questions

How to convert screen pixels to map units

DaveLewis73 — Mon, 28 Feb 2022 20:56:20 GMT

I am looking to create polygons (halos/rings) around the mouse cursor. I have figured out how to create the halos by using System.Windows.Forms.Control.MousePosition and then converting into lat/long by using MapView.Active.ScreenToMap. I have also used a MouseHook from the Win32Api to give me a MouseMove event. This allows me to associate the polygon to the mouse cursor and move it around the map as an overlay.

The problem that I am having now is that I can only create a polygon (halo/ring) with a radius in pixels. I need to be able to use map units, like feet, meters, miles, kilometers, etc. For example, I want to create a polygon (halo/ring) that has a radius of 100 feet.

Is there some way to accomplish this?

The following is a method that I am using that takes pixels to create the halo, just in case it would be of help to someone:

private ArcGIS.Core.Geometry.Polygon CreateHaloPolygon(MapPoint mapPoint, int pixels, out double radius)
{
// Get the halo radius
Point screenPoint = MapView.Active.MapToScreen(mapPoint);
Point radiusScreenPoint = new Point((screenPoint.X + pixels), screenPoint.Y);
MapPoint radiusMapPoint = MapView.Active.ScreenToMap(radiusScreenPoint);
radius = GeometryEngine.Instance.Distance(mapPoint, radiusMapPoint);

// Build a circle geometry
Coordinate2D coord2D = new Coordinate2D(mapPoint);
EllipticArcSegment arcSegment = EllipticArcBuilder.CreateEllipticArcSegment(coord2D, radius, esriArcOrientation.esriArcClockwise, SpatialReferences.WGS84); //MapView.Active.Map.SpatialReference);
PolygonBuilder polyBuilder = new PolygonBuilder(new[] { arcSegment });

return polyBuilder.ToGeometry();
}

Re: How to convert screen pixels to map units

KenBuja — Thu, 24 Feb 2022 20:25:28 GMT

Does the snippet Calculate Selection tolerance in map units help at all in converting from screen pixel to map units?

Re: How to convert screen pixels to map units

DaveLewis73 — Thu, 24 Feb 2022 20:27:31 GMT

Ken,

Thank you for your reply. Unfortunately, I have already come across that sample and it doesn't work for me.

Re: How to convert screen pixels to map units

GKmieliauskas — Fri, 25 Feb 2022 06:35:48 GMT

Hi,

Have tried EllipticArcBuilder ?

More info here:

https://github.com/Esri/arcgis-pro-sdk/blob/master/Examples/Geometry/ProSnippets.cs

Re: How to convert screen pixels to map units

DaveLewis73 — Fri, 25 Feb 2022 21:42:37 GMT

Gintautas,

Thanks for the link. I looked it over and I did find some interesting information concerning LinearUnits, but I didn't find an answer to my question regarding the conversion of screen coordinates in pixels to map units.

Re: How to convert screen pixels to map units

DaveLewis73 — Tue, 15 Mar 2022 16:15:52 GMT

I have solved this issue by using the GeometryEngine.Instance.GeodesicEllipse method. It takes in a GeodesicEllipseParamter containing all of the necessary parameters to create the ellipse and a spatial reference. Included in the parameters is the radius and the linear units to use. The following is a code snippet of creating the geodesic ellipse:

private ArcGIS.Core.Geometry.Geometry BuildBufferEllipse(MapPoint mapPt, double radius, string linearUnits)
{
var ellipseParams = new GeodesicEllipseParameter
{
Center = new Coordinate2D(mapPt),
AxisDirection = 0.0,
LinearUnit = GetLinearUnits(linearUnits),
OutGeometryType = GeometryType.Polygon,
SemiAxis1Length = radius,
SemiAxis2Length = radius,
VertexCount = 99
};

return GeometryEngine.Instance.GeodesicEllipse(ellipseParams, MapView.Active.Map.SpatialReference);
}