Drawing Tangent Lines

[Anonymous]

I've hit upon an annoying defficiency in ArchiCAD, again, and I'm wondering if anybody out there has a solution (aka: workaround).

How do you draw a line that's tangent to two circles? I have a site plan with property lines at some odd angles which are not dimensioned. All I have to go on is some dimensions that locate the corner of the building. Going the reverse route, I need to ... [long story short] ... draw a line that's tangent to 2 circles.

I've tried two different ways of constructing the tangent line geometrically, but the solution always ends up being "slighly" off (depending on the scale. For a site plan you're talking feet - a considerable problem).

So does anybody have any suggestions?

Thanks in advance.

[Anonymous]

Sergio,
Do a search on Archicad-Talk, keyword tangent.
There has been considerable discussion on this issue.
Peter Devlin

[Anonymous]

Here it is

[Djordje]

Sergio wrote:
How do you draw a line that's tangent to two circles?

http://archicad-talk.graphisoft.com/viewtopic.php?t=485

http://archicad-talk.graphisoft.com/viewtopic.php?p=2456#2456

HTH,

[Steve Jepson]

Deleted

[Anonymous]

Adalbert wrote:
Here it is

Oh wow, finally a method that works. Thank you very much Adalbert. Maybe this one should be posted in the tips 'n tricks section as the only accurate and simple working way of drawing tangents (to 2 circles or between a point and a circle), or until GS decides to help us out with a tangent command. Like I said before, none of the other ways of constructing a tangent were accurate to me, and I'd seen and tried them before (thank you anyway guys).

However, I would think that a tangent command should be standard in any CAD software. Maybe I'm asking for too much since I don't need this EVERY day, but...

The only additional explanation/clarification I'd like to make is that if the circles intersect each other, you need to scale them down appropiately so you can use this method.

[Laszlo Nagy]

This is also accurate:
http://archicad-talk.graphisoft.com/viewtopic.php?p=15166&highlight=tangent#15166
Laszlo

[Anonymous]

Could be accurate, but it seems to involve more drafting (you have to know the radius of one, subtract the radius of the other, etc). I don't remember if I've tried it out or not - if I did, I either messed up or... ?

But thanks for pointing that out. It's good to see people listen (and help)...