Calculate a Defined Area (.NET)

If the area you want to calculate is based on user specified points, you might consider creating an in memory object such as a lightweight polyline, and then query of the area of the object before discarding it. The following steps explain how you might accomplish this:

Use the GetPoint method in a loop to obtain the points from the user.
Create a lightweight polyline from the points provided by the user. Create a new Polyline object. Specify the number of vertices and the points they should be at.
Use the Area property to obtain the area of the newly created polyline.
Dispose of the polyline using its Dispose method.

Calculate the area defined by points entered from the user

This example prompts the user to enter five points. A polyline is then created out of the points entered. The polyline is closed, and the area of the polyline is displayed in a message box. Since the polyline is not added to a block, it needs to be disposed before the command ends.

VB.NET

Imports Autodesk.AutoCAD.ApplicationServices
Imports Autodesk.AutoCAD.DatabaseServices
Imports Autodesk.AutoCAD.Geometry
Imports Autodesk.AutoCAD.EditorInput
Imports Autodesk.AutoCAD.Runtime
 
<CommandMethod("CalculateDefinedArea")> _
Public Sub CalculateDefinedArea()
    '' Prompt the user for 5 points
    Dim acDoc As Document = Application.DocumentManager.MdiActiveDocument
 
    Dim pPtRes As PromptPointResult
    Dim colPt As Point2dCollection = New Point2dCollection
    Dim pPtOpts As PromptPointOptions = New PromptPointOptions("")
 
    '' Prompt for the first point
    pPtOpts.Message = vbLf & "Specify first point: "
    pPtRes = acDoc.Editor.GetPoint(pPtOpts)
    colPt.Add(New Point2d(pPtRes.Value.X, pPtRes.Value.Y))
 
    '' Exit if the user presses ESC or cancels the command
    If pPtRes.Status = PromptStatus.Cancel Then Exit Sub
 
    Dim nCounter As Integer = 1
 
    While (nCounter <= 4)
        '' Prompt for the next points
        Select Case nCounter
            Case 1
                pPtOpts.Message = vbLf & "Specify second point: "
            Case 2
                pPtOpts.Message = vbLf & "Specify third point: "
            Case 3
                pPtOpts.Message = vbLf & "Specify fourth point: "
            Case 4
                pPtOpts.Message = vbLf & "Specify fifth point: "
        End Select
 
        '' Use the previous point as the base point
        pPtOpts.UseBasePoint = True
        pPtOpts.BasePoint = pPtRes.Value
 
        pPtRes = acDoc.Editor.GetPoint(pPtOpts)
        colPt.Add(New Point2d(pPtRes.Value.X, pPtRes.Value.Y))
 
        If pPtRes.Status = PromptStatus.Cancel Then Exit Sub
 
        '' Increment the counter
        nCounter = nCounter + 1
   End While
 
    '' Create a polyline with 5 points
    Using acPoly As Polyline = New Polyline()
        acPoly.AddVertexAt(0, colPt(0), 0, 0, 0)
        acPoly.AddVertexAt(1, colPt(1), 0, 0, 0)
        acPoly.AddVertexAt(2, colPt(2), 0, 0, 0)
        acPoly.AddVertexAt(3, colPt(3), 0, 0, 0)
        acPoly.AddVertexAt(4, colPt(4), 0, 0, 0)
 
        '' Close the polyline
        acPoly.Closed = True
 
        '' Query the area of the polyline
        Application.ShowAlertDialog("Area of polyline: " & _
                                    acPoly.Area.ToString())
 
        '' Dispose of the polyline
    End Using
End Sub

C#

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Geometry;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
 
[CommandMethod("CalculateDefinedArea")]
public static void CalculateDefinedArea()
{
    // Prompt the user for 5 points
    Document acDoc = Application.DocumentManager.MdiActiveDocument;
 
    PromptPointResult pPtRes;
    Point2dCollection colPt = new Point2dCollection();
    PromptPointOptions pPtOpts = new PromptPointOptions("");
 
    // Prompt for the first point
    pPtOpts.Message = "\nSpecify first point: ";
    pPtRes = acDoc.Editor.GetPoint(pPtOpts);
    colPt.Add(new Point2d(pPtRes.Value.X, pPtRes.Value.Y));
 
    // Exit if the user presses ESC or cancels the command
    if (pPtRes.Status == PromptStatus.Cancel) return;
 
    int nCounter = 1;
 
    while (nCounter <= 4)
    {
        // Prompt for the next points
        switch(nCounter)
        {
            case 1:
                pPtOpts.Message = "\nSpecify second point: ";
                break;
            case 2:
                pPtOpts.Message = "\nSpecify third point: ";
                break;
            case 3:
                pPtOpts.Message = "\nSpecify fourth point: ";
                break;
            case 4:
                pPtOpts.Message = "\nSpecify fifth point: ";
                break;
        }
 
        // Use the previous point as the base point
        pPtOpts.UseBasePoint = true;
        pPtOpts.BasePoint = pPtRes.Value;
 
        pPtRes = acDoc.Editor.GetPoint(pPtOpts);
        colPt.Add(new Point2d(pPtRes.Value.X, pPtRes.Value.Y));
 
        if (pPtRes.Status == PromptStatus.Cancel) return;
 
        // Increment the counter
        nCounter = nCounter + 1;
    }
 
    // Create a polyline with 5 points
    using (Polyline acPoly = new Polyline())
    {
        acPoly.AddVertexAt(0, colPt[0], 0, 0, 0);
        acPoly.AddVertexAt(1, colPt[1], 0, 0, 0);
        acPoly.AddVertexAt(2, colPt[2], 0, 0, 0);
        acPoly.AddVertexAt(3, colPt[3], 0, 0, 0);
        acPoly.AddVertexAt(4, colPt[4], 0, 0, 0);
 
        // Close the polyline
        acPoly.Closed = true;
 
        // Query the area of the polyline
        Application.ShowAlertDialog("Area of polyline: " +
                                    acPoly.Area.ToString());
 
        // Dispose of the polyline
    }
}

VBA/ActiveX Code Reference

This example prompts the user to enter five points. A polyline is then created out of the points entered. The polyline is closed, and the area of the polyline is displayed in a message box. Unlike the AutoCAD .NET API examples, the polyline is not created in memory but as a database resident object and added to Model space. So after the area of the polyline is obtained, it is removed.

Sub CalculateDefinedArea()
    Dim p1 As Variant
    Dim p2 As Variant
    Dim p3 As Variant
    Dim p4 As Variant
    Dim p5 As Variant
 
    ' Get the points from the user
    p1 = ThisDrawing.Utility.GetPoint(, vbCrLf & "Specify first point: ")
    p2 = ThisDrawing.Utility.GetPoint(p1, vbCrLf & "Specify second point: ")
    p3 = ThisDrawing.Utility.GetPoint(p2, vbCrLf & "Specify third point: ")
    p4 = ThisDrawing.Utility.GetPoint(p3, vbCrLf & "Specify fourth point: ")
    p5 = ThisDrawing.Utility.GetPoint(p4, vbCrLf & "Specify fifth point: ")
 
    ' Create the 2D polyline from the points
    Dim polyObj As AcadLWPolyline
    Dim vertices(0 To 9) As Double
    vertices(0) = p1(0): vertices(1) = p1(1)
    vertices(2) = p2(0): vertices(3) = p2(1)
    vertices(4) = p3(0): vertices(5) = p3(1)
    vertices(6) = p4(0): vertices(7) = p4(1)
    vertices(8) = p5(0): vertices(9) = p5(1)
    Set polyObj = ThisDrawing.ModelSpace.AddLightWeightPolyline _
                      (vertices)
    polyObj.Closed = True
 
    ' Display the area for the polyline
    MsgBox "The area defined by the points is " & _
           polyObj.Area, , "Calculate Defined Area"
 
    ' Remove the polyline
    polyObj.Delete
End Sub

Calculate a Defined Area (.NET)

Calculate the area defined by points entered from the user

VB.NET

C#

VBA/ActiveX Code Reference

Related Concepts