About those construction lines

Rhino Rhino for Mac
1

I want to mark a point 3mm from the beginning of an arc to draw another arc that is not exactly parallel to the first. I would also like to be able to make the other end of the arc 2mm from the already existing arc. With construction lines I can easily establish these points to draw to. What is a similar technique in Rhino?

2

HI James - I think the From OSnap may be the thing.

Arc StartPoint From (snap to the end of the existing arc)
3 & Enter
Ortho (if needed, over to the left, see how you’re constrained to 3 units from the From point.
Click

From again, click on the other end of the arc,
2 & Enter
Ortho to the left and click to set the end point.

?

-Pascal

3

Where can I find this ‘arc from’ option?

4

From is not a Arc option it is a form of constraint always available when Rhino is asking for a point - type ‘From’…

-Pascal

5

Maybe you could link me to a vid demo of this execution?

6

Here it is in Windows Rhino - should be about the same:

http://screencast.com/t/uqlctuy96TpC

-Pascal

7

“From” is a very nice little feature, @pascal (and news to me)! I’ve either missed this in the documentation, or it’s a hidden secret worthy of including in the basics if not there.

While you’re on the topic, any other nifty gems related to geometry construction that you can point us to?

EDIT: Disregard this erroneous sentence and see the one below! Sorry for the flawed recollection!
(Here, I think of the users who are also not aware of creating coordinates with a single “r” prefix to place a point relative to one’s CPlane (which may be moved from World), rather than the default behavior of coordinates relating to the World origin.)

EDIT: The prior sentence should read:
(Here, I think of the users who are also not aware of creating coordinates with a single “r” prefix to place a point relative to one’s last point [such as the second point for a line], rather than the default behavior of coordinates relating to the World origin.)

~Dave

8

??? It seems to work the other way around with my Rhino, no prefix = relative to CPlane, “w” as prefix = world coordinates.

Max.

9

Zoiks… Yes, Max, you’re correct—I was working from memory and flubbed up. VERY SORRY!

What I was thinking of was using “r” as a prefix when entering coordinates (say, for an end of a line not drawn from 0,0,0) so that the default world coordinates are not used. (One sees the “r” prefix in the dynamic display, so that’s a great clue!).

CPlane relocation behaves as you’ve said. Thanks for waking me up! ~Dave