PolygonsWithHoles.cs

This example demonstrates how to create a shapefile holding circular polygons with holes. Here is a screenshot with the results of the code.

using System;
using System.Windows.Forms;
using AxMapWinGIS;
using MapWinGIS;
using System.Diagnostics;

public partial class MapExamples
{
    // <summary>
    // Creates a shapefile holding polygons with holes
    // </summary>
    public void PolygonsWithHoles(AxMap axMap1)
    {
        Shapefile sf = new Shapefile();
        bool result = sf.CreateNewWithShapeID("", ShpfileType.SHP_POLYGON);

        if (!result)
        {
            MessageBox.Show(sf.get_ErrorMsg(sf.LastErrorCode));
        }
        else
        {
            double xMin = 0.0;
            double yMin = 0.0;
            double xMax = 1000.0;
            double yMax = 1000.0;
            Random rnd = new Random(DateTime.Now.Millisecond);

            // builds 10 polygons            
            for (int i = 0; i < 40; i++)
            {
                double xCenter = xMin + (xMax - xMin) * rnd.NextDouble();
                double yCenter = yMin + (yMax - yMin) * rnd.NextDouble();

                // random radius from 10 to 100
                double radius = 10 + rnd.NextDouble() * 90;

                Shape shp = new Shape();
                shp.Create(ShpfileType.SHP_POLYGON);
                
                // polygon must have clockwise order of points (first argument - true)
                this.AddRing(true, xCenter, yCenter, radius, ref shp);

                // holes must have counter-clockwise order of points (fale for the last argument) 
                this.AddRing(false, xCenter + radius / 2.0, yCenter, radius / 4.0, ref shp) ;
                this.AddRing(false, xCenter - radius / 2.0, yCenter, radius / 4.0, ref shp);
                this.AddRing(false, xCenter, yCenter + radius / 2.0, radius / 4.0, ref shp);
                this.AddRing(false, xCenter, yCenter - radius / 2.0, radius / 4.0, ref shp);

                for (int j = 0; j < shp.NumParts; j++)
                {
                    Debug.Print("Part is clocwise: " + shp.get_PartIsClockWise(j).ToString());
                }

                Debug.Print("Shape is valid: " + shp.IsValid);
                if (!shp.IsValid)
                    Debug.Print("Reason: " + shp.IsValidReason);

                sf.EditInsertShape(shp, ref i);
            }

            axMap1.AddLayer(sf, true);
            axMap1.ZoomToLayer(0);

            sf.SaveAs(@"c:\polygons.shp", null);
        }
    }

    // <summary>
    // Adds a ring to the polygon
    // </summary>
    private void AddRing(bool clockWise, double x, double y, double radius, ref Shape shp)
    {
        int partIndex = shp.NumParts;
        if (shp.numPoints > 0)
            shp.InsertPart(shp.numPoints, ref partIndex);

        int count = 0;
        for (int j = 0; j < 37; j++)
        {
            double dx = radius * Math.Cos(j * Math.PI / 18);
            double dy = radius * Math.Sin(j * Math.PI / 18);
            
            //dx *= clockWise ? -1 : 1;
            dy *= clockWise ? -1 : 1;

            Point pnt = new Point();
            pnt.x = x + dx;
            pnt.y = y + dy;

            count = shp.numPoints;
            shp.InsertPoint(pnt, ref count);
        }
    }
}