Intersection of lines in 3D (in case of a tower)

[Anonymous]

Dear users, 

I am drawing the centerlines of a steel tower and I am trying to make the different intersections of the different centerlines of the bar elements. When I am using "extend" it makes a longer line many times and there is no intersection (e.g. after I can not trim and whem I am turning in 3D i found a gap from an other viewing angle). I didn`t find any solution to make an automatice intersection between lines, and not even a solution to check that 2 lines have an intersection or not.. It is really annoying to be honest, because in this case it is not possible to solve a case like this.

I would really appreciate any usable suggestion!!

Thanks in advance!

[Patchy]

I wild suggestion here, why don't you draw the jib as a solid 3d and slice at the connections to put your braces in ?

[Anonymous]

Thank you for your answer, however I am not sure that I understand you correctly... Maybe a little bit more explanation could help for me.

This is an imported wireframe from solidworks, but there was no option to set the centerlines of the bars. Therefore I started to draw them in autocad. So the geometry has been given from the solidworks model. And I have the braces, but i dont see where the connections are exactly in the terms of the centerlines, what I need.

At the beggining I just use the extension, but it extends even when the lines were not in the same plane! Which i thought is not possible (?!) and therefore there is a small gap, when I am zooming in.

[steve216586]

If it were me. I'd make construction lines and circles. Using M2P between supports and tangent circles where needed.

[Anonymous]

I really appreciate your answers, but sorry I dont understand what you mean with this one sentence solution. I am sure you know what you are talking about, but for me a picture or a modified file can be great!

[Patchy]

Can you explain more of what you wanted to do?

This drawing was made from SW, then you want to use it as an example to draw with autocad?

What type of steel members are you using? Angles? channels? pipe?

Kind a difficult to draw to centerline of nothing, all your drawing shows are lines, what about connections? Plates or  welds ?.......

[Kent1Cooper]

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@s141943 wrote:

.... 

I am drawing the centerlines of a steel tower and I am trying to make the different intersections of the different centerlines of the bar elements. When I am using "extend" it makes a longer line many times and there is no intersection (e.g. after I can not trim and whem I am turning in 3D i found a gap from an other viewing angle). I didn`t find ... a solution to check that 2 lines have an intersection or not.. ....

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The EXTEND command is affected by your view direction, which may be why it's not giving you a true intersection.

If they are Line entities, you can find whether or not they have an intersection [either already, or if one or both need to be extended to make them intersect] in 3D.  In simplest terms [none of the usual bells and whistles, and assuming you don't miss in picking, etc.]:

(setq

  line1 (car (entsel "\nSelect one Line: "))

  line2 (car (entsel "\nSelect other Line: "))

  int (inters (cdr (assoc 10 line1)) (cdr (assoc 11 line1)) (cdr (assoc 10 line2)) (cdr (assoc 11 line2)) nil)

)

If that returns a point, you can use it with a CHANGE command [make sure Ortho is off] to take one of the Lines to that intersection.  If it returns nil, they are not in the same plane, because they [or their extensions] need to truly intersect in 3D for (inters) to find where.

[steve216586]

Draw a series of construction lines. (lines which do not plot)

From your original post, it seems as if your center lines cross imaginary points between cross member supports and the tower centerline. To find the true center of these points, you may have to use the command M2P (middle of two points).

Once you have the grid set up with construction lines, it should be pretty simple to draw your center lines. One from base to top, in the center of tower. Then individual ones from cross support locations to centerline of tower. Or interesection of cross supports, to centerline of tower.

If you have radial components, construction lcircles may serve you as well. You can snap perpendicular from the circle to your tower centerline.

[Anonymous]

Dear Kent1Cooper,

Thank you for this code and your kind answer.

I tried to check some of my lines, but unfortunately it doesn`t work. I attached a picture, it came back with an error message. Or I might missed something?!

[Anonymous]

Dear Patchy,

There was a model in solidworks, but I would like to use the model in a fem software. Unfortunately there is no direct import option between solidworks and fem. Therefore i am using autocad to save the model into dwg, which will be importable into the fem software to make a model for calculation. 

But in solidworks I can not set the centerline, which is necessary to the fem model to make the model with the steel bars and profiles (solid steel bars). In solidworks the profiles just intersect on their cylinder surface. Therefore Ijust immported the simple wirefram of the solidworks and now I am drawing the centerlines, which I will need in the fem software.

[Kent1Cooper · Accepted solution]

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@s141943 wrote:

.... 

I tried to check some of my lines, but unfortunately it doesn`t work. I attached a picture, it came back with an error message. Or I might missed something?!

---

My fault -- I forgot to extract the entity data before extracting information from it.  Try:

(setq

  line1 (entget (car (entsel "\nSelect one Line: ")))

  line2 (entget (car (entsel "\nSelect other Line: ")))

  int (inters (cdr (assoc 10 line1)) (cdr (assoc 11 line1)) (cdr (assoc 10 line2)) (cdr (assoc 11 line2)) nil)

)

[Anonymous]

Dear Ken1Cooper!

Now it is working! It is a great tool and help at least to check that I have an intersection or not ! Thank you very much!

[Anonymous]

Dear steve216586,

Thank you the explanation with the construction lines, to be very frank I did not use them usually. In the meantime, I have an initial problem with them. For example if the 2 lines wich I would like to use (to find the parallel construction line between them, or to extend a line perpendicular to another one) they need to be in the same plane of course. Which is usually not the case when I am doing the inclined "arms" of the tower.

I tried to find any example about the usage of the construction lines, but I did not find anything useful for my case.