Comparing geometry of two features to get changes using ArcObjects and c#?

Question

I would like to compare the geometry between two feature, Already I selected the two feature. How do I start the comparison?

depend on the image below I need to write code to compare this two features and get the difference (blue colour is different) and save the difference in a new feature class,

ITopologicalOperator2 pTopOpOld = oldFeature.ShapeCopy as ITopologicalOperator2;
ITopologicalOperator2 pTopOpNew = newFeature.ShapeCopy as ITopologicalOperator2;

IGeometry differenceGeometry = pTopOpOld.Difference(newFeature.Shape);

pTopOpOld = differenceGeometry as ITopologicalOperator2;
pTopOpOld.IsKnownSimple_2 = false;
pTopOpOld.Simplify();
newFeature.Shape = pTopOpOld as IGeometry;
newFeature.Store();

Answer 1

You are using difference but what you really want is Symmetric Difference (the bits of both input features that aren't common). Look at the pictures in both links, they will help you understand what each method does.

ITopologicalOperator2 pTopOpOld = oldFeature.ShapeCopy as ITopologicalOperator2;
// ITopologicalOperator2 pTopOpNew = newFeature.ShapeCopy as ITopologicalOperator2; // Not used.

IGeometry differenceGeometry = pTopOpOld.Difference(newFeature.ShapeCopy );// always use shapecopy or bad things can happen

pTopOpOld = differenceGeometry as ITopologicalOperator2;
pTopOpOld.IsKnownSimple_2 = false;
pTopOpOld.Simplify();
newFeature.Shape = pTopOpOld as IGeometry;
newFeature.Store();

This of course has some assumptions:

1. Both geometries are polygon.
2. newFeature is a new IFeature created with its IFeatureClass.CreateFeature and not an IFeatureBuffer created by IFeatureClass.CreateFeatureBuffer, which needs to be inserted on an insert cursor, not stored, if you try to store an IFeatureBuffer object you will get a method not found error.

Answer 2

        IWorkspaceFactory workspaceFactory = new ESRI.ArcGIS.DataSourcesGDB.FileGDBWorkspaceFactory();
        IFeatureWorkspace featureWorkspace1 = (IFeatureWorkspace)workspaceFactory.OpenFromFile(shapeFileName, 0);
        IFeatureClass featureClass1 = featureWorkspace1.OpenFeatureClass("geometryChanges");

        IFeatureBuffer feature = featureClass1.CreateFeatureBuffer();
        #region Catch New and compare with old

        ITopologicalOperator2 pTopOpNew = newFeature.ShapeCopy as ITopologicalOperator2;
        IGeometry differenceGeometry = pTopOpNew.Difference(oldFeature.Shape);

        feature.Shape = differenceGeometry;

        UpdateFieldValuesToChanges(featureClass1, feature, uniqueId, "GAINED");
        #endregion

        #region Catch Old and compare with new

        IFeatureBuffer featureOld = featureClass1.CreateFeatureBuffer();
        ITopologicalOperator pTopOpOld = oldFeature.ShapeCopy as ITopologicalOperator;
        IGeometry differenceGeometryO = pTopOpOld.Difference(newFeature.Shape);
        featureOld.Shape = differenceGeometryO;
        UpdateFieldValuesToChanges(featureClass1, featureOld, uniqueId, "REDUCED");
        
        #endregion