3d points & 2d polylines

forgot to mention, this is in VB.Net.

I need to draw a polyline between two selected points (and then do some stuff to it). What is my best way forwards? The book I am "learning" (you learn from your mistakes don't you) shows me how to manipulate 2d polylines and how to select 3d points. What I can't do is convert my 3d points into 2d ones. What am I missing?

Are you saying you want to draw a 2D polyline, but you want to snap to 3D points and ignore the Z elevation?

That was quick!

I have also just realised I missed out the important point that I am coding in VB.Net. (sorry)

All I need is a 2d (z=0) polyline.

[font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]Dim[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2] myPline [/size][/font][/size][/font][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]As[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]New[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af]Polyline[/color][/size][/font]
[/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2]myPline.AddVertexAt(0, [/size][/font][/size][/font][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]New[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af]Point2d[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2](0, 0), 0, 0, 0) [/size][/font][/size][/font][font=Consolas][size=2][color=#008000][font=Consolas][size=2][color=#008000][font=Consolas][size=2][color=#008000]' myStartPoint[/color][/size][/font]
[/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2]myPline.AddVertexAt(1, [/size][/font][/size][/font][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]New[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af]Point2d[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2](10, 10), 0, 0, 0) [/size][/font][/size][/font][font=Consolas][size=2][color=#008000][font=Consolas][size=2][color=#008000][font=Consolas][size=2][color=#008000]'myNextPoint[/color][/size][/font]
[/color][/size][/font][/color][/size][/font]

The only commands I (currently) know get me 3d points....

[font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]Dim[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2] my3dStartPoint [/size][/font][/size][/font][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]As[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af]Point3d[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2] = DocumentManager.MdiActiveDocument.Editor.GetPoint([/size][/font][/size][/font][font=Consolas][size=2][color=#a31515][font=Consolas][size=2][color=#a31515][font=Consolas][size=2][color=#a31515]"start "[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2]).Value[/size][/font]
[/size][/font][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]Dim[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2] my2dStartPoint [/size][/font][/size][/font][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff][font=Consolas][size=2][color=#0000ff]As[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af][font=Consolas][size=2][color=#2b91af]Point2d[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2] = DocumentManager.MdiActiveDocument.Editor.GetPoint([/size][/font][/size][/font][font=Consolas][size=2][color=#a31515][font=Consolas][size=2][color=#a31515][font=Consolas][size=2][color=#a31515]"start "[/color][/size][/font][/color][/size][/font][/color][/size][/font][font=Consolas][size=2][font=Consolas][size=2]).Value[/size][/font][/size][/font]

The first one works, the second one doesn't. I am not sure if I am missing a simple conversion or if I have used the wrong components or have just missed a bit with my syntax.

Dave,

The Value Property of EditorInput.PromptResult... Which is what is returned by Editor.GetPoint()... returns a Point3d, which is why your attempt to cast as Point2d fails.

To obtain a single Point2d from a Point3d, consider using the X, and Y values of the Point3d to create a new Point2d.

If you have List and want to convert to List, Tony offers some good advice here.

Here's a simple Extension Method for your use, that will allow you to immediately extract the Point2d from any Point3d Type (even from EditorInput.PromptResult.Value as I'll show below):

namespace Autodesk.AutoCAD.Geometry
{
   public static class Point3dExtensionMethods
   {
       public static Point2d GetPoint2d(this Point3d pt)
       {
           return new Point2d(pt.X, pt.Y);
       }
   }
}

... And here's a quick example of it's use:

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Geometry;
using Autodesk.AutoCAD.Runtime;

[color="blue"]using Autodesk.AutoCAD.Geometry.Point3dExtensionMethods;[/color]

namespace CADTutor.Sample.PointUtilities
{
   class Foo
   {
       [CommandMethod("FOO")]
       void FOO()
       {
           Document doc =
                   Application.DocumentManager.MdiActiveDocument;

           Editor ed = doc.Editor;

           PromptPointOptions opts = new PromptPointOptions("");

           opts.Message = "\nSpecify a point: ";

           PromptPointResult ppr = ed.GetPoint(opts);

           if (ppr.Status == PromptStatus.OK)
           {
               Point3d pt = ppr.Value;

               ed.WriteMessage(
                   "\n** [Point3d] = {0}, [Point2d] = {1} ** ",
                   pt.ToString(),
                   pt.[color="blue"]GetPoint2d()[/color].ToString()
               );
           }
       }
   }
}

You may also find this ADNDevBlog article useful:

Extension methods in AutoCAD 2013

Hi Dave, see simple code in attachment,

this is an oldie but it's working for me yet

loop_points.txt

thanks both, I'll have a proper look tomorrow when I get back to work.

Yet again I didn't look for the simple solution of just dropping the z component of a 3d point!

On the way home it occured to me that I would also have to work out how to "announce" that the pline should be closed - it looks like fixo has that already in his code.

Tony offers some good advice here.

..........

For a simple conversion (e.g, Z = 0.0), don't use Convert2d()

because it transforms the input point into the plane argument.

It's more efficient to just return a new Point2d.

..........

I see, you are commenting on fixo's use of Convert2d(). I can see this will take a little time....

That is correct... Fixo is one of my heroes, and I have learned a great deal from him (and am sure I will continue to do so in the future), I only ventured out on the branch of credibility to correct one of my heroes as a result of Tony's explicit comment regarding efficiency... Tony being someone both Fixo and I greatly respect.

I certainly do not mean to sound argumentative, nor am I suggesting that Fixo's code is insufficient in any way (it obviously works), but given Tony's comments on efficiency, I chose to offer the above Extension Method.

Feel free to use whatever you feel appropriate, as I am very much still a student.

Cheers