Hi Marc,

> I've observed that the tangent snap mode operate differently than the

> Tangent circle Function;

> If I start a ordinary 3 points circle near a circle (with only tangent mode

> enabled), I can't seem to obtain a tangent point.

Yes, this is kind of a long standing area of confusion in drawing circles.

The problem is that the tangent snap is only about placing a point tangent from the previous picked point - this is not the same thing as placing the generated circle to be tangent. The Tangent circle command on the other hand is focused on placing the generated circle and not just picked points.

Here is a visual example. Say you are drawing a circle with the "3 pts" tool, and you have finished picking the first 2 points and are currently in progress of picking the 3rd point like this:

If you move your mouse to the curve for the 3rd point, you will find a tangent snap there:

However, as you can see the circle is not tangent to the curve, what is tangent here is the line formed between the second point (that is the previous picked point) and the current point, here I have drawn the tangent line in red, you can see it goes directly through the point that was labeled "2" above:

That's all that tangent snap does, it finds a tangent to a curve from the previous picked point, it works the same if you are drawing a line, circle, curve, etc... It's always a tangent in a straight line from the previous picked point.

When you use the Circle tangent tool, it doesn't use the tangent snap anymore, it does a completely different calculation that is focused on making the generated circle tangent to the curves you picked on.

> It makes it hard to construct a circle or an arc with only one tangent reference.

Sometimes it is easiest to use perpendicular snap to generate tangent circles.

So for example if I want to create a circle through a given point tangent to the curve:

If you use the Circle Diam (By 2 diameter points) command, you can place the first point on that point away from the curve, and then for the second point use perp snap, that will create a circle tangent to the curve.

Similarly you can use the circle from center point - basically if you place the center of a circle along a perpendicular that is another way to create tangency.

If you have one that you are having problems with, can you please post the .3dm model file so I can take a look?

> Also, having the"start,end,on" option in 3pt circle (Like3pt arc) could be great.

Well, any 3 points will create the same circle shape regardless of the order you pick them in... For arcs it is a little different because the arc has a start and end point.

- Michael