topic Re: Re : how to modified arc's StartPoint or EndPoint in .NET Forum

how to modified arc's StartPoint or EndPoint

Anonymous — Thu, 19 Jan 2017 03:21:10 GMT

Arc's StartPoint or EndPoint is read only.How to modify them?

Re : how to modified arc's StartPoint or EndPoint

_gile — Thu, 19 Jan 2017 06:46:31 GMT

Hi,

If you want to modify an arc start point, you have to specify antother data than the arc end point to defin a new arc (e.g. start or end angle, another point on the arc...).

Re : how to modified arc's StartPoint or EndPoint

Anonymous — Thu, 19 Jan 2017 06:53:21 GMT

as above pic,we can draw the endpoint or startpoint modify the arc in acad.I found the arc's radiu had changed.How to mimic that?

Re : how to modified arc's StartPoint or EndPoint

_gile — Thu, 19 Jan 2017 07:39:19 GMT

When editing the arc end point or start point using the grips, AutoCAD keeps the arc middle point as "point on arc" so tha the new arc is defined with 3 points.

The CircularArc3d geometry object which have a constructor which takes 3 points as arguments can be use for this task.

        public void EditArcEndPoint(Arc arc, Point3d endPoint)
        {
            Point3d midPoint = arc.GetPointAtParameter((arc.StartParam + arc.EndParam) / 2.0);
            CircularArc3d circArc = new CircularArc3d(arc.StartPoint, midPoint, endPoint);
            var angle = Vector3d.XAxis.GetAngleTo(arc.StartPoint - circArc.Center, circArc.Normal);
            if (!arc.IsWriteEnabled)
                arc.UpgradeOpen();
            arc.Center = circArc.Center;
            arc.Normal = circArc.Normal;
            arc.Radius = circArc.Radius;
            arc.StartAngle = circArc.StartAngle + angle;
            arc.EndAngle = circArc.EndAngle + angle;
        }

Re: Re : how to modified arc's StartPoint or EndPoint

Anonymous — Tue, 22 Jun 2021 15:39:57 GMT

Hello @_gile ,

I have two point3d .

I would like the arc to go from point A to point B,
but with the ARC method we cannot generate an ARC from point A to point B, it asks us for the center and angles, which I cannot know.

What I want is easy to do on Autocad, we link the two points and we choose a 3rd point, or a direction, or an angle.

I am thinking of generating a function with
ARC (startpoint, endpoint) but I'm failing for now.

I try with this code but i'm failing now.

Point3d A = new Point3d(1,1,0) Point3d B = new Point3d(11,11,0) Point3d C = new Point3d(12/2,12/2,0); BlockTable acBlkTbl; acBlkTbl = tr.GetObject(db.BlockTableId,OpenMode.ForRead) as BlockTable; // Open the Block table record Model space for write BlockTableRecord acBlkTblRec; acBlkTblRec = tr.GetObject(acBlkTbl[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord; Arc arc = new Arc(); Point3d midPoint = arc.GetPointAtParameter((arc.StartParam + arc.EndParam) / 2.0); CircularArc3d circArc = new CircularArc3d(A, C, B); var angle = Vector3d.XAxis.GetAngleTo(arc.StartPoint - circArc.Center, circArc.Normal); if (!arc.IsWriteEnabled) arc.UpgradeOpen(); arc.Center = circArc.Center; arc.Normal = circArc.Normal; arc.Radius = circArc.Radius; arc.StartAngle = circArc.StartAngle + angle; arc.EndAngle = circArc.EndAngle + angle; acBlkTblRec.AppendEntity(arc); tr.AddNewlyCreatedDBObject(arc, true); } // Save the new line to the database tr.Commit();

Re: Re : how to modified arc's StartPoint or EndPoint

_gile — Tue, 22 Jun 2021 16:27:09 GMT

Hi,

Two points aren't enough to define an Arc. You need to provide at least one other data, a third point on the arc, the center of the arc, the arc angle, the start tangent, ...

Re: Re : how to modified arc's StartPoint or EndPoint

Anonymous — Wed, 23 Jun 2021 07:31:24 GMT

exactly !
So, I have my starting point and my end point, I want there to be the connection in the shape of an arc of a circle.
can the 3rd value be random or something else?

Because I'm trying to develop but for now it's complicated

Or my question is :

We can edit the EndPoint and the Start Point too ?

Re: Re : how to modified arc's StartPoint or EndPoint

Anonymous — Wed, 23 Jun 2021 07:51:01 GMT

Sometimes I'm not very clear and I apologize

But I managed to do that

and that's what I wish I had 🙂

This is my code 🙂

Point3d A = new Point3d(1,1,0) Point3d B = new Point3d(11,11,0) Point3d C = new Point3d(12/2,12/2,0) BlockTable acBlkTbl; acBlkTbl = tr.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable; BlockTableRecord acBlkTblRec; acBlkTblRec = tr.GetObject(acBlkTbl[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord; Arc arc = new Arc(); EditArcEndPoint(arc, B); EditArcEndPoint(arc, A); acBlkTblRec.AppendEntity(arc); tr.AddNewlyCreatedDBObject(arc, true); } tr.Commit(); } } public static void EditArcEndPoint(Arc arc, Point3d endPoint) { Point3d midPoint = arc.GetPointAtParameter((arc.StartParam + arc.EndParam) / 2.0); CircularArc3d circArc = new CircularArc3d(arc.StartPoint, midPoint, endPoint); var angle = Vector3d.XAxis.GetAngleTo(arc.StartPoint - circArc.Center, circArc.Normal); if (!arc.IsWriteEnabled) arc.UpgradeOpen(); arc.Center = circArc.Center; arc.Normal = circArc.Normal; arc.Radius = circArc.Radius; arc.StartAngle = circArc.StartAngle + angle; arc.EndAngle = circArc.EndAngle + angle; } public static void EditArcStartPoint(Arc arc, Point3d Start) { Point3d midPoint = arc.GetPointAtParameter((arc.StartParam + arc.EndParam) / 2.0); CircularArc3d circArc = new CircularArc3d(Start, midPoint, arc.EndPoint); var angle = Vector3d.XAxis.GetAngleTo(Start - circArc.Center, circArc.Normal); if (!arc.IsWriteEnabled) arc.UpgradeOpen(); arc.Center = circArc.Center; arc.Normal = circArc.Normal; arc.Radius = circArc.Radius; arc.StartAngle = circArc.StartAngle + angle; arc.EndAngle = circArc.EndAngle + angle; }

Thanks a lot @_gile

Re: Re : how to modified arc's StartPoint or EndPoint

Anonymous — Wed, 23 Jun 2021 08:36:45 GMT

I found the answer!

You answered the question on another forum 🙂

You are the best 🙂

Re: Re : how to modified arc's StartPoint or EndPoint

_gile — Wed, 23 Jun 2021 13:26:43 GMT

@Anonymous a écrit :

I found the answer!

You answered the question on another forum 🙂

This is not exactly the same question, The topic was: "Create arc through 3 points".

Re: Re : how to modified arc's StartPoint or EndPoint

Anonymous — Mon, 05 Jul 2021 10:31:35 GMT

Hello @_gile !

I managed to draw an arc of a circle between two consecutive points, but the arc of a circle is too large because the position of the center of the circle is located between the two points, but I have not found a solution to have a less imposing arc of a circle.

look at

https://forums.autodesk.com/t5/net/draw-an-arc-of-a-circle-not-very-wide-from-a-starting-point-to/td-p/10443808

to see what i want to explain please 🙂