BoundingCurve.cs

using System;
using System.Collections.Generic;
using ESRI.ArcGIS.DataSourcesRaster;
using ESRI.ArcGIS.Geodatabase;
using ESRI.ArcGIS.Geometry;

internal enum CurveDirection { RIGHT, UP, LEFT, DOWN };

public sealed class BoundingCurve
{
    private int m_Width;
    private int m_Height;
    private bool[,] m_IsFilled;
    private bool[,] m_CellVisited;

    public BoundingCurve (bool[,] grid) {
        m_IsFilled = grid;
        m_Width = grid.GetLength(0);
        m_Height = grid.GetLength(1);
        m_CellVisited = new bool[m_Width, m_Height];
        m_CellVisited.Initialize();
    }

    public List<List<System.Drawing.Point>> GetBoundaryAsList () {
        List<List<System.Drawing.Point>> result = new List<List<System.Drawing.Point>>();
        for (int x = 0; x <= m_Width; x += 1) {
            for (int y = 0; y <= m_Height; y += 1) {
                if ((!CellVisited(x, y)) && IsFilled(x, y) && (!IsFilled(x - 1, y))) {
                    result.Add(GetCurve(x, y));
                }
            }
        }
        return result;
    }

    public IPolygon GetBoundaryAsPolygon (IRasterProps props) {
        double left = props.Extent.XMin;
        double top = props.Extent.YMax;
        IPnt cellSize = props.MeanCellSize();
        PolygonClass result = new PolygonClass();
        object missing = Type.Missing;
        for (int x = 0; x <= m_Width; x += 1) {
            for (int y = 0; y <= m_Height; y += 1) {
                if ((!CellVisited(x, y)) && IsFilled(x, y) && (!IsFilled(x - 1, y))) {
                    List<System.Drawing.Point> bmRing = GetCurve(x, y);
                    RingClass ring = new RingClass();
                    foreach (System.Drawing.Point bmPt in bmRing) {
                        PointClass point = new PointClass();
                        point.PutCoords(left + bmPt.X * cellSize.X,
                                        top - bmPt.Y * cellSize.Y);
                        ring.AddPoint(point, ref missing, ref missing);
                    }
                    result.AddGeometry(ring, ref missing, ref missing);
                }
            }
        }
        return result;
    }

    private bool IsFilled (int x, int y) {
        if ((x < 0) || (y < 0) || (x >= m_Width) || (y >= m_Height)) {
            return false;
        } else {
            return m_IsFilled[x, y];
        }
    }

    private bool CellVisited (int x, int y) {
        if ((x < 0) || (y < 0) || (x >= m_Width) || (y >= m_Height)) {
            return false;
        } else {
            return m_CellVisited[x, y];
        }
    }

    private void MarkVisited (int x, int y) {
        if ((x >= 0) && (x < m_Width) && (y >= 0) && (y < m_Height)) {
            m_CellVisited[x, y] = true;
        }
    }

    private List<System.Drawing.Point> GetCurve (int startX, int startY) {
        MarkVisited(startX, startY);
        List<System.Drawing.Point> result = new List<System.Drawing.Point>();
        result.Add(new System.Drawing.Point(startX, startY));
        int x = startX;
        int y = startY + 1;
        CurveDirection direction = CurveDirection.UP;
        while ((x != startX) || (y != startY)) {
            CurveDirection newDirection = direction;
            switch (direction) {
                case CurveDirection.UP:
                    if (IsFilled(x - 1, y) && IsFilled(x, y)) {
                        newDirection = CurveDirection.LEFT;
                        MarkVisited(x - 1, y);
                    } else if (IsFilled(x, y)) {
                        newDirection = CurveDirection.UP;
                        MarkVisited(x, y);
                    } else {
                        newDirection = CurveDirection.RIGHT;
                    }
                    break;
                case CurveDirection.RIGHT:
                    if (IsFilled(x, y) && IsFilled(x, y - 1)) {
                        newDirection = CurveDirection.UP;
                        MarkVisited(x, y);
                    } else if (IsFilled(x, y - 1)) {
                        newDirection = CurveDirection.RIGHT;
                        MarkVisited(x, y - 1);
                    } else {
                        newDirection = CurveDirection.DOWN;
                    }
                    break;
                case CurveDirection.DOWN:
                    if (IsFilled(x, y - 1) && IsFilled(x - 1, y - 1)) {
                        newDirection = CurveDirection.RIGHT;
                        MarkVisited(x, y - 1);
                    } else if (IsFilled(x - 1, y - 1)) {
                        newDirection = CurveDirection.DOWN;
                        if ((x < 2) || IsFilled(x - 2, y - 1))
                            MarkVisited(x - 1, y - 1);
                    } else {
                        newDirection = CurveDirection.LEFT;
                    }
                    break;
                case CurveDirection.LEFT:
                    if (IsFilled(x - 1, y - 1) && IsFilled(x - 1, y)) {
                        newDirection = CurveDirection.DOWN;
                        if ((x < 2) || IsFilled(x - 2, y - 1))
                            MarkVisited(x - 1, y - 1);
                    } else if (IsFilled(x - 1, y)) {
                        newDirection = CurveDirection.LEFT;
                        MarkVisited(x - 1, y);
                    } else {
                        newDirection = CurveDirection.UP;
                        MarkVisited(x, y);
                    }
                    break;
                default:
                    throw (new Exception("this shouldn't happen"));
            }

            result.Add(new System.Drawing.Point(x, y));

            switch (newDirection) {
                case CurveDirection.UP:
                    y += 1;
                    break;
                case CurveDirection.RIGHT:
                    x += 1;
                    break;
                case CurveDirection.DOWN:
                    y -= 1;
                    break;
                case CurveDirection.LEFT:
                    x -= 1;
                    break;
            }
            direction = newDirection;
        }

        // Be absolutely sure the curve is closed
        if (!result[0].Equals(result[result.Count - 1])) {
            result.Add(new System.Drawing.Point(startX, startY));
        }

        result.Reverse();
        return result;
    }
}