C#+AE 判斷點是否在面內的方法
public double getXMinValue(IPolygon nPolygon)
{
IPolygon sPolygon;
sPolygon = nPolygon;
IPointCollection pPointCollection;
pPointCollection = sPolygon as IPointCollection;
int n = pPointCollection.PointCount;
double[] coordX = new double[n];
for (int i = 0; i < n; i++)
{
IPoint point = pPointCollection.get_Point(i);
coordX[i] = point.X;
}
//對陣列進行從小到大排序
System.Array.Sort(coordX);
Xmin = coordX[0];
return Xmin;
}
向左畫射線並得到交點個數的程式碼：
try
{
ILine newLine = new LineClass();
IPoint toPoint = new PointClass();
toPoint.PutCoords(getXMinValue(pPolygon) - 20.0000000000000, pPoint.Y);
newLine.PutCoords(pPoint, toPoint);//給新的直線賦予起始座標
//苗師兄想法
IPolyline l = new PolylineClass();
l.FromPoint = pPoint;
l.ToPoint = toPoint;
IGeometryCollection pPolyline = new PolylineClass();
ISegmentCollection pPath;
pPath = new PathClass();
object missing1 = Type.Missing;
object missing2 = Type.Missing;
pPath.AddSegment(newLine as ISegment, ref missing1, ref missing2);
pPolyline.AddGeometry(pPath as IGeometry, ref missing1, ref missing2);
IElement element = DrawLineSymbol(pPolyline as IGeometry, pColor);
pGraph.AddElement(element, 0);
pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGraphics, null, null);
ITopologicalOperator pTopo = pPolygon as ITopologicalOperator;//pPolygon多邊形
IGeometryCollection pGeoCol = pTopo.Intersect((IGeometry)l, esriGeometryDimension.esriGeometry0Dimension) as IGeometryCollection; //執行到這一句有問題；
IPointCollection pPointCol = pGeoCol as IPointCollection;
if ((pPointCol.PointCount) % 2 == 0)
{
MessageBox.Show("射線和多邊形的交點個數為："+pPointCol.PointCount.ToString()+",點在多邊形外。");
}
else
{
MessageBox.Show("射線和多邊形的交點個數為："+pPointCol.PointCount.ToString()+",點在多邊形內。");
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
本文是按照Polygon物件考慮的面，所以並未考慮重疊面的問題。
最近幫別人解決了一個問題，如何判斷一個座標點，是否在多邊形區域內（二維）。
在網上搜索了一圈，都是自己寫程式碼，有多種演算法，分凸多邊形、凹多邊形，總之是麻煩。
繼續搜尋，瞭解到 Java/dotnet 自帶的類庫中，都有現成的類函式，可以解決這個問題。
考慮到了解的人不多，特將相關知識共享出來，也許大家以後也用得著。
a) dotnet 中，用 System.Drawing.Drawing2D.GraphicsPath 和 Region 類聯合起來，然後用 Region.IsVisible(point) 函式，可以判斷點是否在多邊形區域內。
b) Java 中，使用 java.awt.Polygon.contains(point) ，或者 java.awt.geom.GeneralPath.contains(point) 函式，都可以判斷點是否在多邊形區域內。
以下是程式碼示例：
code c#:
System.Drawing.Drawing2D.GraphicsPath myGraphicsPath=new System.Drawing.Drawing2D.GraphicsPath();
Region myRegion=new Region();
myGraphicsPath.Reset();
//添家多邊形點
Point p1=new Point(x1,y1);
Point p2=new Point(x2,y2);
Point p3=new Point(x3,y3);
Point p4=new Point(x4,y4);
myGraphicsPath.AddPolygon(LoadPoint(p1,p2,p2,p4));
myRegion.MakeEmpty();
myRegion.Union(myGraphicsPath);
//返回判斷點是否在多邊形裡
bool myPoint =myRegion.IsVisible(MousePoint);
code java 1:
public boolean checkWithJdkGeneralPath(Point2D.Double point, List<Point2D.Double> polygon) {
java.awt.geom.GeneralPath p = new java.awt.geom.GeneralPath();
Point2D.Double first = polygon.get(0);
p.moveTo(first.x, first.y);
for (Point2D.Double d : polygon) {
p.lineTo(d.x, d.y);
}
p.lineTo(first.x, first.y);
p.closePath();
return p.contains(point);
}
code java 2:
public boolean checkWithJdkPolygon(Point2D.Double point, List<Point2D.Double> polygon) {
java.awt.Polygon p = new Polygon();
// java.awt.geom.GeneralPath
final int TIMES = 1000;
for (Point2D.Double d : polygon) {
int x = (int) d.x * TIMES;
int y = (int) d.y * TIMES;
p.addPoint(x, y);
}
int x = (int) point.x * TIMES;
int y = (int) point.y * TIMES;
return p.contains(x, y);
}
java.awt.Polygon 好像只能處理整數座標值，不能處理浮點數。