Draw a Box around an Ellipse

[greypaw]

Can someone please explain why, when trying to draw a box around a rotated ellipse - per the attached drawing, I have a lot of difficulty in getting "tangent" snaps to work?

I start with the rotated ellipse and then draw a vertical line to the right.
I now want to draw a tangent from the ellipse to a perpendicular snap on the line...
If I cannot get a "tangent" snap, I draw any line to intersect the ellipse. Now I can get a tangent, but not a TRUE tangent, just some point on the ellipse. If I continue drawing more and more lines as tangents, in the end I get the desired effect (it generally takes about six lines). Does anyone have any similar experience of ellipses?

BTW I know that I can draw an approximated "polyline" ellipse, but this is not what I want.

Many thanks

gp. (aka "confused of ellipseville"!)

[madcadder]

I don't have it... but I'd swear that I've seen a lisp that draws a rectangle around selected objects. Maybe someone here has this timesaver and will upload it.

[jaberwok]

I suppose the math is just too complicated since the ellipse is an arc of constantly varying radius so it doesn't have a single, locatable centre at each end. It's just a pity you can't use the polyline version.

[bmonk]

Can someone please explain why, when trying to draw a box around a rotated ellipse - per the attached drawing, I have a lot of difficulty in getting "tangent" snaps to work?

I start with the rotated ellipse and then draw a vertical line to the right.
I now want to draw a tangent from the ellipse to a perpendicular snap on the line...
If I cannot get a "tangent" snap, I draw any line to intersect the ellipse. Now I can get a tangent, but not a TRUE tangent, just some point on the ellipse. If I continue drawing more and more lines as tangents, in the end I get the desired effect (it generally takes about six lines). Does anyone have any similar experience of ellipses?

BTW I know that I can draw an approximated "polyline" ellipse, but this is not what I want.

Many thanks

gp. (aka "confused of ellipseville"!)

GP, I tried DL'ing the dwg, but it didn't work, however, I think I replicated the example well enough from your description. I drew a rotated ellipse, with a vertical line to the right.

The only way to get a line tangent to ellipse and perp to line is to:

1) copy ellipse to other side of line.
2) type "xline" (construction line)
3) snap tangent from ellipse to ellipse.
4) trim appropriately.

and if its a box your after, then just copy in all 4 directions, rinse and repeat.

HTH

Brian

[greypaw]

Brian.
Hi.
Thanks for your interest.
I'm sorry the dwg didn't work. (It was an ACAD2007 format file...)
- if you are still interested, I've saved the file as a 2004 format now. attached here.
I tried what you describe, but still cannot get "tangent" snaps to work!
In fact although I can get (some sort of a) tangent using the line command, xline does not work at all.
I guess this may become one of life's unsolved mysteries!

[madcadder]

SOLUTION!

Yesterday, I didn't think BOXTEXT.lsp would work on anything but text. Today, I actually tried it on a 50x25 ellipse rotated 45 and it worked.

This is my modified copy of the routine.
It will create and use a layer called Z-ANNO-NPLT.
There should be no ill effects other than the added layer.

[bmonk]

Brian.
Hi.
Thanks for your interest.
I'm sorry the dwg didn't work. (It was an ACAD2007 format file...)
- if you are still interested, I've saved the file as a 2004 format now. attached here.
I tried what you describe, but still cannot get "tangent" snaps to work!
In fact although I can get (some sort of a) tangent using the line command, xline does not work at all.
I guess this may become one of life's unsolved mysteries!

Sorry to hear you still had problems. For me to get it to work, I had to snap tangent to first ellipse, and then when I snapped tangent to the second ellipse, I had to move the cursor PAST the point of where the tangent would actually be. If that makes any sense.

Anyway, maybe its a 2007 issue, I am using '06.

However, Madcadder's lisp routine seems to work great. Thanks MC, I will be adding it to my Lisproutines.

[greypaw]

Thanks to both of you!
Unfortunately at THIS place of work (I work elsewhere too!), I use LT2007, which clearly won't be able to try the lisp!
I'll report back on Friday, when I'm at a "full-AutoCAD" office!
Further, I tried the xline solution in LT2005 and still cannot get any tangent snaps to work...
Maybe full-ACAD is different --
I think ellipse geometry is just a bit too complex for CAD to cope with predictably.
Still, if MC's lisp works I'll be a "Happy Bunny"!

gp (aka slightly less confused of ellipseville!!)

[greypaw]

The lisp works great!
Just one question...
Does the box actually TOUCH the ellipse? I can't get an intersect snap to work...
With my laborious method, I can, and when I try to trim the ellipse, the command line tells me that it doesn't intersect the line(s) twice -- which is what I'd expect.
Not being "picky", here, guys, just curious!
Thanks again for the help.

gp

[madcadder]

The lisp works great!
Just one question...
Does the box actually TOUCH the ellipse? I can't get an intersect snap to work...
With my laborious method, I can, and when I try to trim the ellipse, the command line tells me that it doesn't intersect the line(s) twice -- which is what I'd expect.
Not being "picky", here, guys, just curious!
Thanks again for the help.

gp

It's off 0.00000001.

The box has a z el of -0.00000001
:dunno:

Help file was no help; will have to look into it more.

[EDIT: apparent intersection works for now]