Intersection between two lines

Unknown said:

Is it possible to know if two straight lines can intersect? 

2D or 3D?  If 3D, you must first check that the lines lie on the same plane.  If non-planar, they never intersect.

Jhon, The lines are in the same plane. I've a DGN 2D.

Jan, I think that i've to use the Ray3dRay3dIntersectXY method but I don't understand the VBA help. Any example?

In the help I need Ray0 and Ray1 that are my lines, but I don't know to put in the Point0, Fraction0, Point1 and Fraction1. Always it's True.

Regards

Dim LineA As LineElementDim LineB As LineElement
Dim sRayA As Ray3dDim sRayB As Ray3dDim boolResultado As Boolean.......................................sRayA.Origin = lineA.Origin
sRayA.Direction = (lineA.EndPoint)
sRayB.Origin = lineB.Origin
sRayB.Direction = (lineB.EndPoint)

boolResultado = Ray3dRay3dIntersectXY(sRayA, sRayB, lineA.EndPoint, -1, lineB.EndPoint, -1)

Jhon, The lines are in the same plane. I've a DGN 2D.

Jan, I think that i've to use the Ray3dRay3dIntersectXY method but I don't understand the VBA help. Any example?

In the help I need Ray0 and Ray1 that are my lines, but I don't know to put in the Point0, Fraction0, Point1 and Fraction1. Always it's True.

Regards

Dim LineA As LineElementDim LineB As LineElement
Dim sRayA As Ray3dDim sRayB As Ray3dDim boolResultado As Boolean.......................................sRayA.Origin = lineA.Origin
sRayA.Direction = (lineA.EndPoint)
sRayB.Origin = lineB.Origin
sRayB.Direction = (lineB.EndPoint)

boolResultado = Ray3dRay3dIntersectXY(sRayA, sRayB, lineA.EndPoint, -1, lineB.EndPoint, -1)

Vector Algebra

The direction of a line is the vector difference between its start point and end point.

Unknown said:

sRayA.Direction = (lineA.EndPoint)

Your direction is the vector from 0,0 to lineA.EndPoint.

Try this …

sRayA.Direction = Point3dSubtract (lineA.EndPoint - lineA.StartPoint)

Regards, Jon Summers
LA Solutions

In addition to Jon's advice, your code should looks like this ...

rayA.Origin = lineAStart
rayA.Direction = Point3dSubtract(lineAEnd, lineAStart)

rayB.Origin = lineBStart
rayB.Direction = Point3dSubtract(lineBEnd, lineBStart)

Dim inter1 As Point3d
Dim fract1 As Double
Dim inter2 As Point3d
Dim fract2 As Double

Dim result As Boolean

result = Ray3dRay3dIntersectXY(rayA, rayB, inter1, fract1, inter2, fract2)

Because you work in 2D only, important for you is only intersection point inter1, that is the same as point inter2. Fractions express where the intersection point is in terms of the length of the particular ray. This information is important if you need to know if the intersection point lies on the line (between start and end points) or outside.

HTH Jan

Ok Jon, I understood perfectly. But I've a problem because always the lines have a intersection. The lines don't have intersection when are paralell.

In my case I need to know if the lines have a intersection in your proyection. In the next image, for my case, the lines don't have intersection because the direction is open. It's possible to know this with the method Ray3dRay3dIntersectXY.

Regards

Unknown said:

In my case I need to know if the lines have a intersection in your proyection

Unknown said:

Fractions express where the intersection point is in terms of the length of the particular ray. This information is important if you need to know if the intersection point lies on the line (between start and end points) or outside.

I think you have an answer.  Follow Jan's advice and examine the value of those fractions.

To be more precise:

• -1 <= fraction <= 1 ... the point is inside the particular ray.
• fraction < 1 or 1 < fraction, the point is outside the start-end points.

Regards,

  Jan

Jon, I didn't see the answer of Jan.

Effectively I have tested the code of Jan and it works. Whit the values of these fractions I resolved the problem.

Thanks both