StartPoint od polyline

[flovo]

Is possible to change the startpoint of a polyline?

eg:

Polyline lwp = obj as Polyline;

int vn = lwp.NumberOfVertices;
for (int i = 0; i < vn; i++)
{
    SegmentType sg = lwp.GetSegmentType(i);

 }

...

lwp.StartPoint = lwp.GetArcSegmentAt(1).StartPoint;

[caddzone]

You can modify the first vertex just as you would any vertex.

[flovo]

Please, could you give me an example?

[caddzone]

You call the PolyLine's SetPointAt() method and pass it the index of

the vertex and the new coordinate.

[flovo]

I tried without success:

Point3d nextpoint = lwp.GetArcSegmentAt(1).StartPoint;
lwp.SetPointAt(0, new Point2d(nextpoint.X, nextpoint.Y));

because the polyline change shape.

[caddzone]

You're trying to set the start point to the second vertex.

You'll have to explain in more detail what you're trying to do.

[flovo]

I've a closed polyline composed by some Arc and Line as in 1.dwg

This polyline has a startpoint at 41.4033981995461,46.6236763815663 (startpoint of the first segment) that I need to change in 43.8777100135197,46.8401506153171 (startpoint of the second segment) before cicllyng with:

int vn = lwp.NumberOfVertices;
for (int i = 0; i < vn; i++)
{
SegmentType sg = lwp.GetSegmentType(i);
...

}

[caddzone]

Isn't it obvious that if you want to change the start point of the first

segment to be the start point of the second segment, what you

actually are doing is deleting the first segment/vertex?

[flovo]

I only want to change the first segment of the polyline.

[caddzone]

Sorry, I really can't figure out what it is you're trying to do.

Perhaps posting a file with the 'before' and 'after' might help.

[flovo]

As attached files before.dwg and after.dwg the first segment of the polyline is different.

My question is: how can I do this programmatically in autocad .net?

[caddzone · Accepted solution]

The only difference I see is that the first vertex is offset by one

vertex in one of the two polylines.

To do this via the API, you either delete the last vertex and

insert it at the start, or delete the first vertex and insert it

at the end.

[flovo]

I don't understand, because I think the last vertex is also the first.

Please, could you explain it with code?

[caddzone]

No, the last vertex is not the first vertex. If a polylline is closed, it

merely means that there is a segment connecting the first and last

vertices. Perhaps you are confusing vertices with the segments

that connect them.

Sorry, I don't have time to write the code for you.

[flovo]

Ok, now I understand:

int vn = lwp.NumberOfVertices;

lwp.RemoveVertexAt(0);
lwp.AddVertexAt(vn - 1, new Point2d(X, Y), 0, 0, 0);

where Point2d(X, Y) is the StartPoint of the Segment at index = 1

Many thanks