Find nearest point between 2 lines in 3D


I’m drawing 2 lines that represent bullet trajectories. Hypothetically 2 bullets were shot into 2 adjacent walls of a building. I’ve created the building and created 2 lines that represent the bullet trajectories (these lines are in 3D as they both have vertical and horizontal angles). Both lines come within a few inches of each other at one point in the middle of the room, representing the hypothetical shooters location at time of firing the bullets. I’m having a hard time figuring out how to best pick a point that represents the CLOSEST point of intersection. I need to keep this as simple as possible as this will be used for a high school class on forensics. Google SketchUp is a tool used in the class to build a model of the crime scene but this is NOT an in-depth CAD class.

The simplest way I can see right now is just to click on the floor and right click and go to “Align View” and then draw a little line that “appears” to go through the apparent intersection of the 2 lines and that gets me, in this case, within an inch and 1/2, which might be reasonable for this example.

I’ll try to upload the file herein.trajectories1.skp (118.7 KB)

How can I do this? Any help would be greatly appreciated!!! Happy Thanksgiving!!



trajectories1.skp (121.0 KB)

Try this, I just draw a flat rectangle to match the angle of the two shots. It makes it easier to see where they intersect. You now have their horizontal intersection, the vertical part, you can just measure the distance and divide by 2 for the average.


Yeah that got me a point on each line that was only 1 1/2" from each other and that was easy and was just as close as all my trial and error got me. Thanks.



Here’s one model which shows one way to construct this:


The shortest connection between the two bullet trajectories A and B (= C = ~1 15/32" or 37,470101mm) is perpendicular to both given edges, the trajectories.

Copy one edge (A) as A’ to intersect anywhere with the other (B). A’/B determine a plane. You now need to make a(ny) close loop (triangle) with A’ and B, to let SketchUp create a face. Use the ‘Push/Pull’ tool to extrude this face. The extrusion’s new sides are all perpendicular to the extruded face, they all at least give you the correct direction of the shortest connection between A and B.
Ectruding two side faces of the created 3D shape with ‘Push/Pull’ +[Ctrl], inferencing on A its endpoint, creates a virtual intersection of two new faces with the desired shortest edge (though you need to actually draw this edge on the virtual intersection).


Here is skp for that form long time ago. You can get a closed form solution if you want a very accurate solutiondraw_normal_to_two_skew_lines.skp (1.3 MB)
BTW not my model