Calculate Areas (.NET)

You can find the area of an arc, circle, ellipse, lightweight polyline, polyline, region, hatch, planar-closed spline or any other entity that is derived from the base type of Curve by using the Area property.

If you need to calculate the combined area of more than one object, you can keep a running total as you add or use the Boolean method on a series of regions to obtain a single region representing the desired area. From this single region you can use the Area property to obtain its area. The calculated area differs according to the type of object you query.

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:

1. Use the GetPoint method in a loop to obtain the points from the user.
2. 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.
3. Use the Area property to obtain the area of the newly created polyline.
4. 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.

C# Example

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
    }
}