Joining Two Tangents with One Line

[Anonymous]

I am experiencing difficulty with ascertaining tangents of two circles, and joining the two tangent points with a line.

Say you have two circles, both of different diameters, and you want to ascertain the tangent points of these two circles, and join the two points together. I have found this task to be nearly impossible. Please refer to the attached image for an illustration of what I am trying to achieve in ArchiCAD 10.

Whenever I get a "tangent" snap symbol and click on it, I realize that the point I got is not really a tangent at all. If I were to zoom in to the maximum possible, I find that the line I created and the circle do not meet at an intersection point at all. In fact, they are apart.

This can be a problem if my floor plan is shaped as such, and I need to ascertain the two tangent points to join and form the straight portion of the external envelope of the building if it were so.

Maybe I am missing something here....has anyone experienced this similar case and found a possible solution for it? Thanks!

[Anonymous]

If you offset circle 1 by the radius of circle 2 you can then draw a line from centre of circle 2 to tangent of offset circle 1, then offset this line again by radius of circle 2.

Make sense?

[Anonymous]

Hey Stuart

I tried it and it works! Thanks!

[Djordje]

There is an extensive explanation in the Tips&Tricks forum, too

[Anonymous]

Extraordinary isn't it! Here we are on version 11 and something as simple as this still cannot be done easily. Archiruler will do it properly but why should we need to purchase an addon to do this.
The woeful shortcomings of Archicads 2d functions really, really need to be addressed.

[Dwight]

Even though i have ArchiRuler that places dual tangentials with ease, i rarely use this feature since Archicad's chamfer/fillet tool rounds intersections in a way compatible with how i design. [NOT being an apologist for Archicad's lack of such a simple drafting aid.]

It requires non-drafting thinking.

Instead of starting with free-floating circles and placing tangential lines and then editing the circles, [lalala] you start with the lines, round their intersections [all at once if wanting a uniform radius], and offset the other side of the roadway [say] as a unit where curves and lines scale together.

In the case of a road segment where offsetting reduces a curve to zero, it is simple enough to re-establish the rounding....

[Anonymous]

troakie wrote:
Extraordinary isn't it! Here we are on version 11 and something as simple as this still cannot be done easily. Archiruler will do it properly but why should we need to purchase an addon to do this.
The woeful shortcomings of Archicads 2d functions really, really need to be addressed.

Why is this not a simple way of doing it? Just plain old geometry. Sometimes we have to think for ourselves.

Admittedly, Autocad would have sorted this easily with 2 tangent points because you can specify what relationship to use rather than waiting for Archicad to find one.