Convert Display Pixels to Map Units Snippet

///<summary>Convert the display extents in Pixels (at the current map scale) and then return out the map units.</summary>
///
///<param name="activeView">An IActiveView interface</param>
///<param name="pixelUnits">A System.Double containing the number of display pixels to convert. Example: 100</param>
/// 
///<returns>A System.Double containing the number of Map Units, -1 is returned if something went wrong.</returns>
/// 
///<remarks></remarks>
public System.Double ConvertPixelsToMapUnits(ESRI.ArcGIS.Carto.IActiveView activeView, System.Int32 pixelUnits)
{
  
  if(activeView == null)
  {
    return -1;
  }
  //Get the ScreenDisplay
  ESRI.ArcGIS.Display.IScreenDisplay screenDisplay = activeView.ScreenDisplay;

  //Get the DisplayTransformation 
  ESRI.ArcGIS.Display.IDisplayTransformation displayTransformation = screenDisplay.DisplayTransformation;

  //Get the device frame which will give us the number of pixels in the X direction
  ESRI.ArcGIS.Display.tagRECT deviceRECT = displayTransformation.get_DeviceFrame();
  System.Int32 pixelExtent = (deviceRECT.right - deviceRECT.left);

  //Get the map extent of the currently visible area
  ESRI.ArcGIS.Geometry.IEnvelope envelope = displayTransformation.VisibleBounds;
  System.Double realWorldDisplayExtent = envelope.Width;

  //Calculate the size of one pixel
  if(pixelExtent == 0)
  {
    return -1;
  }
  System.Double sizeOfOnePixel = (realWorldDisplayExtent / pixelExtent);

  //Multiply this by the input argument to get the result
  return (pixelUnits * sizeOfOnePixel);
}

'''<summary>Convert the display extents in Pixels (at the current map scale) and then return out the map units.</summary>
'''
'''<param name="activeView">An IActiveView interface</param>
'''<param name="pixelUnits">A System.Double containing the number of display pixels to convert. Example: 100</param>
''' 
'''<returns>A System.Double containing the number of Map Units, -1 is returned if something went wrong.</returns>
''' 
'''<remarks></remarks>
Public Function ConvertPixelsToMapUnits(ByVal activeView As ESRI.ArcGIS.Carto.IActiveView, ByVal pixelUnits As System.Int32) As System.Double

  If activeView Is Nothing Then
  	Return -1
  End If

  'Get the ScreenDisplay
  Dim screenDisplay As ESRI.ArcGIS.Display.IScreenDisplay = activeView.ScreenDisplay

  'Get the DisplayTransformation 
  Dim displayTransformation As ESRI.ArcGIS.Display.IDisplayTransformation = screenDisplay.DisplayTransformation

  'Get the device frame which will give us the number of pixels in the X direction
  Dim deviceRECT As ESRI.ArcGIS.Display.tagRECT = displayTransformation.DeviceFrame
  Dim pixelExtent As System.Int32 = (deviceRECT.right - deviceRECT.left)

  'Get the map extent of the currently visible area
  Dim envelope As ESRI.ArcGIS.Geometry.IEnvelope = displayTransformation.VisibleBounds
  Dim realWorldDisplayExtent As System.Double = envelope.Width

  'Calculate the size of one pixel
  If pixelExtent = 0 Then
	  Return -1
  End If

  Dim sizeOfOnePixel As System.Double = (realWorldDisplayExtent / pixelExtent)

  'Multiply this by the input argument to get the result
  Return (pixelUnits * sizeOfOnePixel)

End Function