/// <summary>
        /// 新增欄位，以及計算幾何面積
        /// </summary>
        /// <param name="pFeatureLayer">向量圖層</param>
        /// <param name="fieldName">新增的欄位名稱，如：相交面積</param>
        private void AddCalculateField(IFeatureLayer pFeatureLayer, string fieldName)
        {
            //獲取預審生成圖層
            IFeatureClass pFeatureClass = pFeatureLayer.FeatureClass;
            IField pField = null;
            IFieldEdit pFieldEdit = null;
            if (pFeatureClass.Fields.FindField(fieldName) < 0)
            {
                pField = new FieldClass();
                pFieldEdit = pField as IFieldEdit;
                pFieldEdit.Type_2 = esriFieldType.esriFieldTypeDouble;
                pFieldEdit.Name_2 = fieldName;
                pFieldEdit.IsNullable_2 = true;
                pFeatureClass.AddField(pField);
            }
            IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, false);
            IFeature pFeature = pFeatureCursor.NextFeature();
            while (pFeature != null)
            {
                //設定座標系統，計算幾何需要座標系統
                pFeature.Shape.Project(m_spatialReference);

                IArea pArea = (IArea)pFeature.Shape;
                double area = pArea.Area;
                int index = pFeature.Fields.FindField(fieldName);
                pFeature.set_Value(index, area);
                pFeature.Store();
                System.Runtime.InteropServices.Marshal.ReleaseComObject(pFeature);
                pFeature = pFeatureCursor.NextFeature();
            }
            System.Runtime.InteropServices.Marshal.ReleaseComObject(pFeatureCursor);
        }

                IFeatureClass pFeatureClass = m_FeatureLayer.FeatureClass;
                IGeoDataset pGeoDataset = pFeatureClass as IGeoDataset;
                ISpatialReference m_spatialReference = pGeoDataset.SpatialReference;