SelectByDistance.cs

This example demonstrates how to select buildings which lie within specified distance from the parks. Here is a screenshot with the results of the code.


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

public partial class MapExamples
{
    // <summary>
    // Selects buildings which lie within specified distance from the parks.
    // </summary>
    public void SelectByDistance(AxMap axMap1, string dataPath)
    {
        string filename1 = dataPath + "buildings.shp";
        string filename2 = dataPath + "natural.shp";
        
        if (!File.Exists(filename1) || !File.Exists(filename2))
        {
            MessageBox.Show("Failed to open shapefile (natural.shp, buildings.shp): " + dataPath);
            return;
        }

        Shapefile sfBuildings = new Shapefile();
        sfBuildings.Open(filename1, null);

        Shapefile sfParks = new Shapefile();
        sfParks.Open(filename2, null);
        ShapefileCategory ct = sfParks.Categories.Add("Parks");
        
        // choose parks and make them green
        ct.Expression = "[Type] = \"Park\"";
        Utils utils = new Utils();
        ct.DrawingOptions.FillColor = utils.ColorByName(tkMapColor.Green);
        sfParks.Categories.ApplyExpression(0);
        
        // hide the rest types of objects on the layer
        sfParks.DefaultDrawingOptions.Visible = false;

        double maxDistance = 150.0;        // in meters

        bool editing = sfBuildings.StartEditingShapes(true, null);
        sfBuildings.UseQTree = true;   // this will build a spatial index to speed up selection

        for (int i = 0; i < sfParks.NumShapes; i++)
        {
            int index = sfParks.get_ShapeCategory(i);
            if (index == 0)
            {
                object result = null;
                Shape shp = sfParks.get_Shape(i);
                if (sfBuildings.SelectShapes(shp.Extents, maxDistance, SelectMode.INTERSECTION, ref result))
                {
                    int[] shapes = result as int[];
                    for (int j = 0; j < shapes.Length; j++)
                    {
                        if (!sfBuildings.get_ShapeSelected(shapes[j]))
                        {
                            Shape shp2 = sfBuildings.get_Shape(shapes[j]);
                            double dist = shp.Distance(shp2);
                            if (dist < maxDistance)
                                sfBuildings.set_ShapeSelected(shapes[j], true);
                        }
                    }
                }
            }
        }

        axMap1.AddLayer(sfParks, true);
        axMap1.AddLayer(sfBuildings, true);
        axMap1.ZoomToMaxExtents();
    }
}