Converting from GraphicsContainer to Polygon Feature

Question

I have a problem with ArcObjects trying to convert a graphics container filled with segments into a polygon to insert into a feature class. In order to make the jump from a graphics element to a polygon, I believe I have to go from a element to a segment collection that can be inserted into a feature class.

My routine can insert the segments, but the feature class creates a polygon that is missing segments from the beginning or end of the object chain.

This is code I have worked up so far:

public void FinalizeObject(IFeatureLayer layer, IGraphicsContainer graphicsContainer)
    {
        ISegmentCollection segmentCollection = new PolygonClass() as ISegmentCollection;
        IPolygon polygon = new PolygonClass();

        try
        {
            graphicsContainer.Reset();
            IElement element = graphicsContainer.Next();

            while (element != null)
            {
                IGeometry geometry = element.Geometry;
                ISegmentCollection tempClass = new PolygonClass() as ISegmentCollection;
                tempClass = geometry as ISegmentCollection;

                if (tempClass != null && tempClass.SegmentCount > 0)
                {
                    for (int x = 0; x < tempClass.SegmentCount; x++)
                    {
                        ISegment segment = tempClass.Segment[x];
                        segmentCollection.AddSegment(segment);
                        segmentCollection.SegmentsChanged();
                    }
                }
                element = graphicsContainer.Next();
            }

            IFeatureClass featureClass = layer.FeatureClass;
            IFeature feature = featureClass.CreateFeature();
            feature.Shape = (IPolygon)segmentCollection;
        }
        catch (NullReferenceException nre)
        {
            MessageBox.Show(nre.ToString());
        }
    }

What am I missing?

Answer 1

Try this:

public void FinalizeObject(IFeatureLayer layer, IGraphicsContainer graphicsContainer)
{
    ISegmentCollection segmentCollection = new PolygonClass() as ISegmentCollection;
    IPolygon polygon = new PolygonClass();

    try
    {
        graphicsContainer.Reset();
        IElement element = graphicsContainer.Next();
        IFeatureClass featureClass = layer.FeatureClass;

        IGeometry geometry = null;
        while (element != null)
        {
            geometry = element.Geometry;
            IFeature feature = featureClass.CreateFeature();
            feature.Shape = geometry;
            feature.Store();
            element = graphicsContainer.Next();
        }
    }
    catch (NullReferenceException nre)
    {
        MessageBox.Show(nre.ToString());
    }
}

Answer 2

you are not validating that your segments are indeed connected to each others, in the order that you read them. Moreover you are not considering digitization direction. Depending on your data / storage, you may also want to check that the resulting polygon is not multi part.

The doc says "Adding segments to a polygon defined as a SegmentCollection [..] assumes that the polygon is a single ring of connected segments."

You may want to read the graphic container, save each segment in a list. Starting with a random segment (the 1st one to make it easy), you take the TO point coordinates. Then you search in your list the segment having a FROM coordinate equal to the value you just recorded, then read its TO coordinate and continue. If no segment is found, you then check if one has the same TO coordinate (so segment 1 TO = segment X TO). When found, you then reverse its direction and proceed as described above. Make sure that any - and every - segment is used only once (hence the use of a list, allowing you to remove items as they are consumed)