How to draw Perpendicular Lines

[J-Rocks]

Hi,

I am trying to learn how to draw perpendicular lines on Polyline with arc segments by dividing the polyline's length into 15 times in C#.

The length of each drawn Line is = 10.0 units.

Thanks in adnace.

I tried coding it this way and I don't know how to draw the perpendicular lines.

        public static void PerpendicularLines()
        {
            Document doc = Application.DocumentManager.MdiActiveDocument;
            Database db = doc.Database;
            Editor ed = doc.Editor;
            using (Transaction tr = db.TransactionManager.StartTransaction())
            {
                PromptEntityOptions op = new PromptEntityOptions("\nSelect polyline :");
                op.SetRejectMessage("Must be Polyline");
                op.AddAllowedClass(typeof(Polyline), true);
                op.AllowNone = false;
                PromptEntityResult s = ed.GetEntity(op);
                if (s.Status == PromptStatus.OK)
                {
                    Polyline ent = (Polyline)tr.GetObject(s.ObjectId, OpenMode.ForRead);
                    Line drawLine = new Line();
                    double length = ent.Length;
                    double gap = length / 15.0;
                    double dis = gap;
                    int run = ((int)gap);
                    for (int i = 0; i < run; i++)
                    {
                        Point3d p1 = ent.GetPointAtDist(dis);
                        Vector3d ang = ent.GetFirstDerivative(ent.GetParameterAtPoint(p1));
                        // I lost here and don't know how to create the lines ...
                        dis = dis + gap;
                    }
                }
                tr.Commit();
            }
        }

[_gile]

Hi,

The GetfirstDerivative() function return a unit vector which direction is the tangent to the curve at specified point.

Rotating this vector of 90° (PI / 2 radians) will return a unit vector perpendicular to the curve at specified point.

Then, some very basic math/geomety should allow you to scale the vector and use it to get the displaced points.

[J-Rocks]

Thank you gile,

sadly I couldn't solve it because these functions are completely new to me and I don't know how to play with them at the mean time.

[_gile · Accepted solution]

IMO, If you want to draw in AutoCAD with code, you should learn at least the geometric operators and functions of the Point3d, Vector3d and Matrix3d types.

        public static void PerpendicularLines()
        {
            Document doc = Application.DocumentManager.MdiActiveDocument;
            Database db = doc.Database;
            Editor ed = doc.Editor;
            using (Transaction tr = db.TransactionManager.StartTransaction())
            {
                PromptEntityOptions op = new PromptEntityOptions("\nSelect polyline :");
                op.SetRejectMessage("Must be Polyline");
                op.AddAllowedClass(typeof(Polyline), true);
                op.AllowNone = false;
                PromptEntityResult s = ed.GetEntity(op);
                if (s.Status == PromptStatus.OK)
                {
                    Polyline ent = (Polyline)tr.GetObject(s.ObjectId, OpenMode.ForRead);
                    Line drawLine = new Line();
                    double length = ent.Length;
                    double gap = length / 15.0;
                    double dis = gap;
                    //int run = ((int)gap); <- this is wrong and unusefull
                    var curSpace = (BlockTableRecord)tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
                    for (int i = 0; i < 14; i++)
                    {
                        Point3d p1 = ent.GetPointAtDist(dis);
                        Vector3d ang = ent.GetFirstDerivative(ent.GetParameterAtPoint(p1));
                        // scale the vector by 5.0 (so that it's 5 units length)
                        ang = ang.GetNormal() * 5.0;
                        // rotate the vector
                        ang = ang.TransformBy(Matrix3d.Rotation(Math.PI / 2.0, ent.Normal, Point3d.Origin));
                        // create a line by substracting and adding the vector to the point (displacing the point)
                        Line line = new Line(p1 - ang, p1 + ang);
                        curSpace.AppendEntity(line);
                        tr.AddNewlyCreatedDBObject(line, true);
                        dis = dis + gap;
                    }
                }
                tr.Commit();
            }
        }

[J-Rocks]

---

@_gile wrote:

IMO, If you want to draw in AutoCAD with code, you should learn at least the geometric operators and functions of the Point3d, Vector3d and Matrix3d types.

---

Thank you gile for your help and for writing the codes for me that was wonderful.

Yes I should learn about the geometric operations and sadly the AutoCAD.net Help document does not have all funtions , for example the GetParameterAtPoint and GetPointAtDist .... etc are not or I couldn't find any reference for them in the .NET help document to read about them.

Do you have any good reference for AutoCAD.net C# ?

Mant thanks.

[_gile]

By my side, I use the ObjectARX 20XX SDK which contains the required libraries (dll) for .NET developping and the documentation.

The docs folder contains an arxmgd 20XX.chm file for managed code (.NET) only and also all the ObjectARX docs.

You can download them from this page.

[J-Rocks]

Perfect gile , Many thanks

[dgorsman]

Boning up on vector math and trig is also recommended, IMO.  Matrix algebra might be useful in some places, but only so far as to grasp some of the transformation methods.

[J-Rocks]

---

@dgorsman wrote:

Boning up on vector math and trig is also recommended, IMO.  Matrix algebra might be useful in some places, but only so far as to grasp some of the transformation methods.

---

Thank you for your input dgorsman.

Can you post an example please?

[_gile]

---

dgorsman a écrit :

Boning up on vector math and trig is also recommended, IMO.  Matrix algebra might be useful in some places, but only so far as to grasp some of the transformation methods.

---

I agree, matrix algebra knowledge isn't really required with .NET as the API provides built-in methods for the main operations (linear transformations, inversion, combinations, ...) which is not the case with LISP.

[dgorsman]

That, and lot of the legwork you've posted over the years.

Now where's that beer smiley...

[dgorsman]

For example, vector cross products: https://en.wikipedia.org/wiki/Cross_product

Just about everything in AutoCAD 3D space boils down into vector math.

From your original problem you have a vector at any given point (direction of line), and a normal vector pointing straight up (0,0,1); the cross product of the two is mutually perpendicular and only needs to be scaled for length.

Highly useful when dealing with planes.  I can define an arbitrary plane using a point in space and a normal vector (e.g. a viewing direction); using that, I can determine if a second point is on the plane by creating a vector from the point on the plane to the second point.  If the cross product of the two vectors is 0 they are mutually perpendicular and they are on the same plane.  A variation of the technique is used to project points onto a plane such as a viewport.

[BKSpurgeon]

Hi can you post a picture of the final result for completeness of the solution. folks (including me) will be interested to see it.

rgds

BK