Union discards ellipses

DanNarsavage_IDWR — Tue, 13 Jan 2026 20:10:18 GMT

Running an addin in ArcGIS Pro v3.3. When `GeometryEngine.Instance.Union(...)` is given ellipses (or apparently anything even created from ellipses), it produces empty geometries. Has anyone seen this before & come up with a workaround? Thanks!

This code . . .

List<Polygon> polygonParts = []; foreach (Layer layer in layers) { // Stuff omitted for brevity polygonFeatures = polygonFeatures.Where(p => p is not null && !p.IsEmpty) .Select(polygon => { // I tried adding this because I figured the elliptical curves were the issue, but clearly not. Note that circles DON'T need this treatment for Union to handle them appropriately. if (polygon.HasCurves) { Log.Information("Pre-densified polygon has {0} vertices and is empty: {1}", polygon.PointCount, polygon.IsEmpty); polygon = (Polygon)GeometryEngine.Instance.DensifyByAngle(polygon, -1); Log.Information("Densified polygon has {0} vertices, is empty({1}), has area({2}), and has curves({3})", polygon.PointCount, polygon.IsEmpty, polygon.Area, polygon.HasCurves); } return polygon; }) .ToArray(); polygonParts.AddRange(polygonFeatures); } Log.Information("Creating a union from {0} selected features in these layers: {1}", polygonParts.Count, layers.Select(layer => layer.Name)); var unionGeometry = await QueuedTask.Run(() => GeometryEngine.Instance.Union(polygonParts)); Log.Information("Unioned geometry has {0} vertices and is empty({1})", unionGeometry.PointCount, unionGeometry.IsEmpty); var unionPolygon = (Polygon)unionGeometry; Log.Information("Unioned polygon has area({0}), and has curves({1})", unionPolygon.Area, unionPolygon.HasCurves);

. . . produces this log when given ellipses (note the zero area, emptiness, and zero vertices) . . .

[11:48:03 INFO v1.0] Pre-densified polygon has 2 vertices and is empty: false [11:48:03 INFO v1.0] Densified polygon has 37 vertices, is empty(false), has area(-11803.5397706948), and has curves(false) [11:48:03 INFO v1.0] Pre-densified polygon has 2 vertices and is empty: false [11:48:03 INFO v1.0] Densified polygon has 37 vertices, is empty(false), has area(-11803.5397706948), and has curves(false) [11:48:03 INFO v1.0] Creating a union from 2 selected features in these layers: ["Graphics Layer"] [11:48:03 INFO v1.0] Unioned geometry has 0 vertices and is empty(true) [11:48:03 INFO v1.0] Unioned polygon has area(0), and has curves(false)

. . . and this log when given circles (note the nonzero area, non-emptiness, and nonzero vertices) . . .

[11:57:40 INFO v1.0] Pre-densified polygon has 2 vertices and is empty: false [11:57:40 INFO v1.0] Densified polygon has 37 vertices, is empty(false), has area(7722.7340715872815), and has curves(false) [11:57:40 INFO v1.0] Pre-densified polygon has 2 vertices and is empty: false [11:57:40 INFO v1.0] Densified polygon has 37 vertices, is empty(false), has area(7722.7340715872815), and has curves(false) [11:57:40 INFO v1.0] Creating a union from 2 selected features in these layers: ["Graphics Layer"] [11:57:40 INFO v1.0] Unioned geometry has 74 vertices and is empty(false) [11:57:40 INFO v1.0] Unioned polygon has area(15445.469156841702), and has curves(false)

Re: Union discards ellipses

DanNarsavage_IDWR — Tue, 13 Jan 2026 23:52:34 GMT

The `DensifyByAngle(...)` method doesn't seem to work, but `Buffer(...)` does. I made this extension method that buffers by a tiny distance then unbuffers by the same distance . . .

using ArcGIS.Core.Geometry; using Serilog; using EsriPolygon = ArcGIS.Core.Geometry.Polygon; namespace IDWR.WREdit.Contracts.Extensions; /// <summary> /// Offers extension methods for Esri geometries /// </summary> public static class EsriGeometryExtensions { /// <summary> /// The <see cref="GeometryEngine"/> class has shown some intolerance for ellipses. This handles the problem by replacing any curves with a splined approximation /// </summary> /// <param name="polygon">Geometry to be splined</param> /// <remarks>See work item 78279</remarks> public static EsriPolygon SplineEllipse(this EsriPolygon polygon) { if (!polygon.HasCurves) return polygon; Log.Debug("Pre-densified polygon has {0} vertices and is empty: {1}", polygon.PointCount, polygon.IsEmpty); polygon = (Polygon)GeometryEngine.Instance.Buffer( GeometryEngine.Instance.Buffer( polygon, 0.1), -0.1); Log.Debug("Densified polygon has {0} vertices, is empty({1}), has area({2}), and has curves({3})", polygon.PointCount, polygon.IsEmpty, polygon.Area, polygon.HasCurves); return polygon; } }

. . . and now the code looks like below, and the polygon that comes out the end is valid even when the inputs include ellipses. Not a fix, but a workaround until the problems in `GeometryEngine` are resolved. Maybe when we finally upgrade past v3.3?

List<Polygon> polygonParts = []; foreach (Layer layer in layers) { // Stuff omitted for brevity polygonFeatures = polygonFeatures.Where(p => p is not null && !p.IsEmpty) .Select(polygon => polygon.SplineEllipse()) .ToArray(); polygonParts.AddRange(polygonFeatures); } Log.Information("Creating a union from {0} selected features in these layers: {1}", polygonParts.Count, layers.Select(layer => layer.Name)); var unionGeometry = await QueuedTask.Run(() => geometryEngine.Union(polygonParts)); Log.Debug("Unioned geometry has {0} vertices and is empty({1})", unionGeometry.PointCount, unionGeometry.IsEmpty); var unionPolygon = (Polygon)unionGeometry; Log.Debug("Unioned polygon has area({0}), and has curves({1})", unionPolygon.Area, unionPolygon.HasCurves);

topic Union discards ellipses in ArcGIS Pro SDK Questions

Union discards ellipses

Re: Union discards ellipses