JSON serialization object with huge IEnumerable

Question

This code is looping over polygons geometries vertices in order to create a list of deltas (distance) between vertices coordinates to compact the geometry before sending it into the web.

Geometry output is expected to be on this format: [[x0, y0, (x0-x1), (y0-y1), (x1-x2), (y1-y2)]]

The output is a JSON object containing a list of features attributes and geometry deltas like this one:

{
    features: [
        {
            attributes : {"CD_MUNCP" : 00000, "NOM_MUNCP": "Name1"},
            geometry : [[5767767, -834778, -10, 199, 99, 332, 9, -9], [5787767, -837709, 123, 33, -31, 121, 0, 12330]]
        }
    ]
}

I am using IEnumerable<> to create the geometry deltas because I thought it would be faster, but it appears this is not really compatible with JSON serialization (it takes very long to serialize) so I transform them using .ToList().

The most important thing with the code is the performance. It seems the bottleneck is the JSON serialization that takes more than 50% of the processing time.

Is there some optimizations or workarounds I can do to improve the performance?

using System;
using System.Collections.Generic;
using fastJSON;
using ESRI.ArcGIS.ADF;
using ESRI.ArcGIS.Geodatabase;
using ESRI.ArcGIS.Geometry;
using ESRI.ArcGIS.esriSystem;

namespace DesktopConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var watch = System.Diagnostics.Stopwatch.StartNew();
            Result result = new Result
            {
                features = CreateResultFeatures().ToList()
            };
            string output = JSON.ToJSON(result);
            watch.Stop();
            Console.WriteLine(watch.ElapsedMilliseconds);
            Console.ReadLine();
        }

        public class Result
        {
            public IEnumerable<ResultFeature> features { get; set; }
        }

        public class ResultFeature
        {
            public Dictionary<string, dynamic> attributes { get; set; }
            public IEnumerable<IEnumerable<int>> geometry { get; set; }
        }

        public static IEnumerable<ResultFeature> CreateResultFeatures()
        {
            IWorkspace gdbWorkspace = FileGdbWorkspaceFromPath(@"\\vnageop1\geod\Maxime\test.gdb");
            IFeatureWorkspace featureWorkspace = (IFeatureWorkspace)gdbWorkspace;
            IFeatureClass featureClass = featureWorkspace.OpenFeatureClass(@"GEO09E04_MUNCP_GEN");
            IQueryFilter queryFilter = new QueryFilterClass();
            queryFilter.SubFields = "CD_MUNCP, NOM_MUNCP, SHAPE";

            int cd_muncp_idx = featureClass.FindField("CD_MUNCP");
            int nom_muncp_idx = featureClass.FindField("NOM_MUNCP");

            using (ComReleaser comReleaser = new ComReleaser())
            {
                IFeatureCursor cursor = featureClass.Search(queryFilter, false);
                comReleaser.ManageLifetime(cursor);
                IFeature feature = null;
                while ((feature = cursor.NextFeature()) != null)
                {
                    ResultFeature resultFeature = new ResultFeature
                    {
                        attributes = new Dictionary<string,dynamic>
                        {
                            { "CD_MUNCP", Convert.ToString(feature.Value[cd_muncp_idx]) },
                            { "NOM_MUNCP", Convert.ToString(feature.Value[nom_muncp_idx]) }
                        },
                        geometry = PolygonToDeltas(feature.Shape as IPolygon4).ToList()
                    };
                    yield return resultFeature;
                }
            }
        }

        public static IEnumerable<IEnumerable<int>> PolygonToDeltas(IPolygon4 polygon)
        {
            IGeometryBag exteriorRingGeometryBag = polygon.ExteriorRingBag;
            IGeometryCollection exteriorRingGeometryCollection = exteriorRingGeometryBag as IGeometryCollection;
            for (int i = 0; i < exteriorRingGeometryCollection.GeometryCount; i++)
            {
                IGeometry exteriorRingGeometry = exteriorRingGeometryCollection.get_Geometry(i);
                IPointCollection exteriorRingPointCollection = exteriorRingGeometry as IPointCollection;
                yield return CreateDeltas(exteriorRingPointCollection);

                IGeometryBag interiorRingGeometryBag = polygon.get_InteriorRingBag(exteriorRingGeometry as IRing);
                IGeometryCollection interiorRingGeometryCollection = interiorRingGeometryBag as IGeometryCollection;
                for (int k = 0; k < interiorRingGeometryCollection.GeometryCount; k++)
                {
                    IGeometry interiorRingGeometry = interiorRingGeometryCollection.get_Geometry(k);
                    IPointCollection interiorRingPointCollection = interiorRingGeometry as IPointCollection;
                    yield return CreateDeltas(exteriorRingPointCollection);
                }
            }
        }

        private static IEnumerable<int> CreateDeltas(IPointCollection pointCollection)
        {
            int previous_x = (int)pointCollection.get_Point(0).X;
            int previous_y = (int)pointCollection.get_Point(0).Y;
            yield return previous_x;
            yield return previous_y;
            for (int i = 1; i < pointCollection.PointCount; i++)
            {
                int current_x = (int)pointCollection.get_Point(i).X;
                int current_y = (int)pointCollection.get_Point(i).Y;
                yield return previous_x - current_x;
                yield return previous_y - current_y;
                previous_x = current_x;
                previous_y = current_y;
            }
        }
    }
}

Answer 1

I haven't access to the ESRI assemblies, so it's impossible to test and comment about performance, but in this:

public static IEnumerable<IEnumerable<int>> PolygonToDeltas(IPolygon4 polygon)
{
  IGeometryBag exteriorRingGeometryBag = polygon.ExteriorRingBag;
  IGeometryCollection exteriorRingGeometryCollection = exteriorRingGeometryBag as IGeometryCollection;
  for (int i = 0; i < exteriorRingGeometryCollection.GeometryCount; i++)
  {
    IGeometry exteriorRingGeometry = exteriorRingGeometryCollection.get_Geometry(i);
    IPointCollection exteriorRingPointCollection = exteriorRingGeometry as IPointCollection;
    yield return CreateDeltas(exteriorRingPointCollection);

    IGeometryBag interiorRingGeometryBag = polygon.get_InteriorRingBag(exteriorRingGeometry as IRing);
    IGeometryCollection interiorRingGeometryCollection = interiorRingGeometryBag as IGeometryCollection;
    for (int k = 0; k < interiorRingGeometryCollection.GeometryCount; k++)
    {
      IGeometry interiorRingGeometry = interiorRingGeometryCollection.get_Geometry(k);
      IPointCollection interiorRingPointCollection = interiorRingGeometry as IPointCollection;
      // ISN'T THIS A BUG:
      yield return CreateDeltas(exteriorRingPointCollection);
    }
  }
}

... it seems that you call CreateDeltas(exteriorRingPointCollection) both in the outer for-loop where it is expected to be called and in the inner for-loop where I would expect this call: CreateDeltas(interiorRingPointCollection). It seems to be a bug? If exteriorRingPointCollection is significantly larger than interiorRingPointCollection that could be a bottleneck for many interior rings per exterior ring?

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By the way: have you tested if sending the absolute coordinates is a real problem?

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From one of your comments below, I understand that the bottleneck must be at:

string output = JSON.ToJSON(result);

The result classes are defined as:

    public class Result
    {
        public IEnumerable<ResultFeature> features { get; set; }
    }

    public class ResultFeature
    {
        public Dictionary<string, dynamic> attributes { get; set; }
        public IEnumerable<IEnumerable<int>> geometry { get; set; }
    }

Where the ResultFeature.attributes is a Dictionary with value as dynamic. You could maybe try to change that to string or object or another defined type.

Alternatively:

You are using fastJSON which I have no experience with. Have you tried Newtonsoft.Json instead?

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If you want to use c++ apis in C# it can be done using external references