topic Can't get intersection point using Entity.IntersectWith sometimes in .NET Forum

Can't get intersection point using Entity.IntersectWith sometimes

tom.zhengGNS4G — Tue, 23 May 2023 04:36:09 GMT

Hi! I'm new to AutoCAD .NET and trying to get the intersection point of 2 lines using Entity.IntersectWith method lately. Usually, it can find the intersection points. but sometimes it doesn't get it when there should be intersection point between 2 lines. Can' t figured it out why. can someone help or give some suggestions? thx!

Below is my code for test. I iterate each 2 lines in all lines selected by user and draw a circle on every intersection point. I write in c#:

```

[CommandMethod("Test")]
public void Test()
{
Active.UsingTransaction(tr =>
{

var lineResult = Selector.GetSelection("\nselect lines: "); //get user selection
if (lineResult.Status != PromptStatus.OK) return;

var lines = new List<Line>();
foreach (var objId in lineResult.Value.GetObjectIds())
lines.Add(objId.GetObject(OpenMode.ForRead) as Line);

for (var i = 0; i < lines.Count; i++)
{
if (i + 1 == lines.Count) break;

for (var j = i + 1; j < lines.Count; j++)
{
Line line1 = lines[i], line2 = lines[j];
var interPts = new Point3dCollection();

line1.IntersectWith(line2, Intersect.OnBothOperands, interPts, IntPtr.Zero, IntPtr.Zero);

if (interPts.Count > 0) Draw.DrawCircle(interPts[0], 1); //draw a circle with radius 1 on intersection point
}
}
});
}

```

Re: Can't get intersection point using Entity.IntersectWith sometimes

_gile — Tue, 23 May 2023 06:54:40 GMT

Hi,

Try with LineSegment3d.IntersectWith instead.

[CommandMethod("Test")] public void Test() { Active.UsingTransaction(tr => { var lineResult = Selector.GetSelection("\nselect lines: "); //get user selection if (lineResult.Status != PromptStatus.OK) return; var lineSegments = lineResult.Value .GetObjectIds() .Select(id => (Line)id.GetObject(OpenMode.ForRead)) .Select(line => new LineSegment3d(line.StartPoint, line.EndPoint)) .ToArray(); for (var i = 0; i < lineSegments.Length - 1; i++) { for (var j = i + 1; j < lineSegments.Length; j++) { var line1 = lineSegments[i]; var line2 = lineSegments[j]; var interPts = line1.IntersectWith(line2); if (interPts != null) Draw.DrawCircle(interPts[0], 1); //draw a circle with radius 1 on intersection point } } }); }

When you post some code:

Use the 'Insert/Edit code sample' button.
If the code calls method from external libraries, provide the libraries source or a link to them.

Re: Can't get intersection point using Entity.IntersectWith sometimes

_gile — Tue, 23 May 2023 07:26:52 GMT

I should have started there.

Are you sure there is an intersection between these lines (i.e. they are on the same plane)?

Re: Can't get intersection point using Entity.IntersectWith sometimes

tom.zhengGNS4G — Tue, 23 May 2023 08:01:44 GMT

I checked all the 'Z' values of line's StartPoint/EndPoint are '0'. Does this mean they are on the same plane? sorry I'm not familiar with AutoCAD.

Re: Can't get intersection point using Entity.IntersectWith sometimes

_gile — Tue, 23 May 2023 08:44:21 GMT

@tom.zhengGNS4G a écrit :

I checked all the 'Z' values of line's StartPoint/EndPoint are '0'. Does this mean they are on the same plane? sorry I'm not familiar with AutoCAD.

Yes, that means all the lines lies on the XY plane.

Another thing, if the lines are far away from the origin (about x0,000,000 units for x and/or y) there may be an accuracy issue. A workaround is moving all lines closer to the origin, get the intersections and move back the lines (and intsection points).

Re: Can't get intersection point using Entity.IntersectWith sometimes

tom.zhengGNS4G — Tue, 23 May 2023 09:01:52 GMT

Thanks for your suggestion! I found that some lines are not on the same plane. The property panel in AutoCAD shows that all lines are on the Z=0 plane. But when I get the position by code it shows that some line's Z value is not 0.

in AutoCAD it shows that all the Z-value is 0.

get the position of same line by code.

so I use a method to transform line to Z=0 plane if it is not.

void transformZAxis(Line line) { line.UpgradeOpen(); if (line.StartPoint.Z != 0) line.StartPoint = line.StartPoint.TransformBy(Matrix3d.Displacement(new Vector3d(0, 0, -line.StartPoint.Z))); if (line.EndPoint.Z != 0) line.EndPoint = line.EndPoint.TransformBy(Matrix3d.Displacement(new Vector3d(0, 0, -line.EndPoint.Z))); line.DowngradeOpen(); }

After all the lines transform to the same plane. it successfully get all the intersection points. Thanks again for your advice.

Re: Can't get intersection point using Entity.IntersectWith sometimes

_gile — Tue, 23 May 2023 09:22:26 GMT

You could simply do:

void transformZAxis(Line line) { line.UpgradeOpen(); if (line.StartPoint.Z != 0) line.StartPoint = new Point3d(line.StartPoint.X, line.StartPoint.Y, 0.0); if (line.EndPoint.Z != 0) line.EndPoint = new Point3d(line.EndPoint.X, line.EndPoint.Y, 0.0); line.DowngradeOpen(); }