Simple line tan two curves fail..why?

draw circle with ‘project’ on, then mirror copy it, select line tan two curves tool, click near A then B, nothing happens…

Unable to line tan two circles.3dm (27.4 KB)

They are planar,


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I tried it using your instruction in my file and it works fine.
So far I can’t come up with a combination that fails.
I’ll try your file.

I can reproduce it in your file if I pick the circles near your leader points.
If I click closer to where the tangent lines will be found, then it works.
So far I can’t figure out why.

If I make my own circles in you file, they do not have this “dead zone”.

Can you give me any details on how your circles were created?

Hi, used circle from centre, and dragged out until at diameter i wanted.
then mirrored the upper from the lower about a horiz datum line. Project was turned on throughout the entire operation of circle making. and off for line making.


That was one of the specific things I tried and my circles were OK; without “dead” zones.

I’ve sent your example on to the developer to see if he can see where it fails in a debug build. Perhaps with that there will be a clue as to the underlying unknown and so far, unrepeatable issue.


I wonder what would happen if you did a setpt on them, snapping them to the a gridline, and tried it again.

Not sure what you mean setPt gives me xyz, so what do i set to where ?

I never use setPt.

Moves them somewhere else maybe, so not sure how useful that is.

I get simple things fail, copy them out to a new rhino, they work, this time though they still fail.


I tried that and bunch of other things like tolerances, curve direction, etc.
Those two circles and copies of them have this dead zone.

If I make new circles following his details, they work fine, even in the same file.
It’s a mystery currently.
Hopefully Mikko will figure out out.

See recent thread where I couldnt get line to go tan from circle to a corner !

drives me nuts.

win7 64bit pro
Nvidia GTX970


That’s for straightening me out John_Brock.

Steve1, what I meant was to use setpt so set all the points on the curves on a single plane, err, not to squash your circles the other way : ) Sorry if I added to your confusion.

Though, usually, if the tangent lines or snaps fail, I’ve got things not on the same plain (edgewise for things.)

I selected them and went projectToPlane delete input yes, still no joy, they were made with project which should minimize non planar anyway.


If you follow your own instructions, can you make another pair of circles that have the same problem?

Ok, tried that, twice and each time it works ok.


There may well be nothing we can find and nothing to fix.

Just one of many instances of simple things failing.

can the deep doewn physics of those circles be explored as to why they have dead zones ?

like why did line tan from curve to corner fail, even when a similar one was drawn, it still failed.

another classic is circle tan tan rad, fails again and again, even if rad is within line length.


Fixing bugs in software basically boils down to getting a repeatable example we can watch fail in a debug build of Rhino.
Then we can determine where the problem is.
Sometimes the fix is in the top level code in the command you were running, and other times, it’s because of starting with bad or inappropriate geometry. These are harder to figure out as we need to go back up the process and figure out where the bad objects are being created.

If we don’t have a reliable, repeatable example with ALL the details to make it happen again, we can’t even begin the process of fixing it.

That’s where you come in.

The problem has been fixed for V6 and will show up in the next public WIP.
The developer could not figure out how the circles got that way, but we have an older, solver that we hooked back up so when the new solver fails as in your example, it will try the old.
In your example, the old solver works.

Thanks for the example file.