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What are the units of measure used for "__tg_edit_circle_radius"?

#1

I see that the current 15 beta now has FeatureDrawnEditOverlayEventArgs.ColumnValues["__tg_edit_circle_radius"] when drawing a circle what are those units of measure? I drew a small circle and the radius was 138365.8010475412 that does not appear to be meters.
image

#2

It uses the unit of your current map (meters in your case), and you’re also correct that it’s not fully accurate.

When projecting the 3D Earth onto a 2D plane, some distortion is unavoidable. With Spherical Mercator (the projection your map is using), that distortion affects distance and area accuracy. As a result, a circle drawn on the map is not a true circle on the Earth’s surface, and the radius you see is based on the projected map—not the real-world distance.

If you need a more accurate measurement, you can use geodesic calculations. For example:

ellipseShape.GetArea(3857, AreaUnit.SquareMeters, DistanceCalculationMode.Haversine);

This calculates the area using a spherical model of the Earth and will give you a more accurate result.

This is a common question when working with map projections. Here’s a related discussion if you’d like to dig deeper:
EllipseShape Innacuracy issues - ThinkGeo UI for Desktop / WPF - ThinkGeo Discussion Forums

#3

Ben,

Thank you. I did forget to do the adjustment. Going forward if using the BlazorTrackMode to generate a circle is using the dictionary key of __tg_edit_circle_radius going to be the best way to derive the radius? Or will there be a property added? Same with the center point using the keys of __tg_edit_circle_center_x and __tg_edit_circle_center_x, keys or a property later. I am going to code it for now as the dictionary keys. I can always change it later.

Thanks,
James R.

#4

James,

I don’t think that’s the best way to use this internal key directly. Let me think about it, we would most likely add some parameters to FeatureDrawnEditOverlayEventArgs, something like following:

  public class FeatureDrawnEditOverlayEventArgs {
      public Feature DrawnFeature { get; }
      public bool IsCircle { get; }
      public double? CircleRadius { get; }
      public PointShape CircleCenter { get; }
  }

I will keep you posted.

Thanks,
Ben

#5

Ben,

I will look for those changes.

Thanks,
James R.

#6

Hi James,

We added FeatureDrawnEditOverlayEventArgs.GeometryInfo where you can get the Circle Information. Pull beta013 and have another try.

Thanks,
Ben