MapWinGeoProc:Utils AreaOfPart

From MapWindow GIS

AreaOfPart

Syntax

 double AreaOfPart(MapWinGIS.Shape polygon, int PartIndex)

Summary

Calculates the area of a part, without taking into consideration any other aspects of the polygon.

Parameters

Returns

A double value that is equal to the area of the part.

Remarks

Coded by Ted Dunsford 6/23/2006, derived from Angela's Area algorithm
Code reference http://astronomy.swin.edu.au/~pbourke/geometry/polyarea/
Cached in MapWinGeoProc\clsUtils\Documentation\
I don't think that we ever want to return a negative area from this function,
even if the part is a hole, because it is being calculated outside of the
context of any other parts. Only the collective Area function should worry about
ascribing a sign value to the individual part areas.

Visual Basic Net 2005 Example Implementation Code

 ' Requires a reference to MapWinGIS
 ' Requires a reference to MapWinGeoProc
 Public Class Form1
     Implements MapWinGIS.ICallback
     Dim mwShapefile As New MapWinGIS.Shapefile
 
     Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
         mwShapefile.Open("C:\temp\Triangles.shp")
         AxMap1.AddLayer(mwShapefile, True)
     End Sub
 
     Private Sub cmdGetArea_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdGetArea.Click
         Dim shape As New MapWinGIS.Shape
         shape = mwShapefile.Shape(0)
         MessageBox.Show("Area 0: " & MapWinGeoProc.Utils.AreaOfPart(shape, 0))
         MessageBox.Show("Area 1: " & MapWinGeoProc.Utils.AreaOfPart(shape, 1))
     End Sub
 
     Public Sub [Error](ByVal KeyOfSender As String, ByVal ErrorMsg As String) Implements MapWinGIS.ICallback.Error
         MessageBox.Show("ErrorMsg")
     End Sub
 
     Public Sub Progress(ByVal KeyOfSender As String, ByVal Percent As Integer, ByVal Message As String) Implements MapWinGIS.ICallback.Progress
         ProgressBar1.Value = Percent
     End Sub
 
 End Class

 ' Requires a reference to MapWinGIS
 ' Requires a reference to MapWinGeoProc
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Text;
 using System.Windows.Forms;
 
 namespace CSharpDemo
 {
     public partial class Form1 : Form, MapWinGIS.ICallback 
     {
         MapWinGIS.Shapefile mwShapefile;
         public Form1()
         {
             InitializeComponent();
         }
         private void cmdGetArea_Click(object sender, EventArgs e)
         {
             MapWinGIS.Shape shape;
             shape = mwShapefile.get_Shape(0);
             MessageBox.Show("Area 0: " + MapWinGeoProc.Utils.AreaOfPart(shape, 0));
             MessageBox.Show("Area 1: " + MapWinGeoProc.Utils.AreaOfPart(shape, 1));
         }
 
         private void Form1_Load(object sender, EventArgs e)
         {
             mwShapefile = new MapWinGIS.ShapefileClass();
             mwShapefile.Open(@"C:\Temp\Triangles.shp", this);
             axMap1.AddLayer(mwShapefile, true);
         }
         public void Error(string KeyOfSender, string ErrorMsg)
         {
             MessageBox.Show(ErrorMsg);
         }
         public void Progress(string KeyOfSender, int Percent, string Message)
         {
             progressBar1.Value = Percent;
         }
     }
 }

Function added to MapWinGeoProc by Ted Dunsford 6/23/2006

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