Center point of a circle

thomthom

No Point at center here either. SUP6.

I use the endpoint inference trick, but when there's many object near or around it it often doesn't want to lock on the centerpoint. No way to further encourage it?

dammerel

so if you have a look at my file housing.skp,
how would you align the dome with the housing ?

Andrew

Gaieus

Andrew,

I "revised" the whole thread here and I guess there is a misunderstanding. The "Point at centre" (or what) command is in the context menu (right click menu) that pops up when you select the circle with the right mouse button and not in the Edit menu.

Well, I simly cannot imagine how you came up with such a disaligned dome shape!

OK. I had a look and found three things:

you cannot use the "Point at cener" command if the entity is not a circle/arc/polygon (whatever whose edges can be selected as a whole and not exploded into its segments). So I made a face for your dome and used the centerpoint.rb on that.
The dome has a base of only a circle with 20 segments while the cylinder above has the default (24) segments. They will never be able to precisely and nicely aligned.
Even the inside and outside facets of your middle ring were not aligned (they were kind of "twisted" out of alignment)

I aligned the dome for you in three steps:

moved it by snapping my new guidepoint to the origin
rotated it along both the red and green axes to make it horizontal
aligned the corresponding endpoints of the cone and ring to show at the same direction (yet see point 2 above - it cannot be perfectly made)

Here's your model in this state

sorgesu

I have always had all extensions enabled and I don't get "point at center" on a right click or on a hard select or anything. Never saw it? Are you sure you guys didn't load someone's ruby script?

Gaieus

I have centerpint.rb but I did indeed disable it to check if its just another place it may reside.
Are you sure that you are only selecting the circle edge (and not the face as well)?

alpro

I didn't load a ruby, I have center point in my edit menu when circle is highlighted and I also have center point in my context menu. SU6 Pro 6.0.1099

Mike

Jean Lemire

Hi Susan, hi folks.

SU 6 Pro Version 6.0.1099 for PC.

See the attached JPG files.

Just ideas.

http://www.sketchucation.com/forums/scf/sas/Newbie/PointAtCenter2.jpg

http://www.sketchucation.com/forums/scf/sas/Newbie/PointAtCenter3.jpg

sorgesu

Doh. I missed the bit about highlighting just the circumferenece. I have it now. Thanks. But generally I think it is faster to use the 'remind" inference. Only when I need to keep the centerpoint for some other use later, would I need the construction point.

dammerel

thank Gaieus for the answer
Andrew

Jim

Just a thought... it's should be possible to make a ruby to always add a centerpoint when drawing a circle.

humanticnc

would be very useful

ronski

Hi, I have also had trouble finding circle centre.

What Susan didn't tell us was, "to use the pencil tool on the segments".

If you draw a circle then still using the pencil the Centre and segments highlight.

Chiefwoodworker

Susan is right. There is no "Point at center" on my SU 6 either. You guys must be drinking a Ruby drink.

Joe....

Julius

i don't remember where i found it (i suppose somewhere in this forum), but this ruby is very useful: just select the circle and then click Plugins>Set Center Point.

centerpoint.rb

Gaieus

And that's not only for circles but other 2D and 3D shapes, too!
Etremely useful when you want to move and/or precisely align complex geometry.

Anssi

@chiefwoodworker said:

Susan is right. There is no "Point at center" on my SU 6 either. You guys must be drinking a Ruby drink.

Joe....

No, Joe,

We have only checked all the checkboxes in the Window>Preferences>Extensions dialog. Actually I don't remember if it is the Ruby Script Examples or Utilities Tools box that adds the Point At Center command.

Anssi

Jim

It's important to understand the method used by the script for finding the centerpoint. It creates a BoundingBox around the selected entities, and the centerpoint is the center of the BoundingBox.

For a circle, this centerpoint happens to be the centerpoint of the circle. This is not true for an arc, or other non-symmetrical 3d objects.

watkins

Dear All,

The inferencing method to find the centre only works if the circle is unexploded, which is not always the case. Very often I need to find the centre of a circle that has somehow lost its circle entity status. Using weld.rb to rejoin all the segments doesn't work as the entity status changes from 'circle' to 'curve', and inferencing won't work. Usually, I draw two temporary diagonals and then place a construction point at the intersection.

Here is a suggestion for a ruby:

call it curve_centre.rb,
select three (3) consecutive end-points (two adjoining line entities), and voila,
a construction point magically appears at the intersection of the mid-point normals.

Has anyone come across such a ruby?

Regards,
Bob

Jim

watkins,

I started some code to find the center of an arc from line segments. My method used some calculations to find the bulge., but I like your idea - it's easier to write. Actually, you would need only 2 segments, right?

watkins

Dear Jim,

Yes, the method could be made to work with only two adjacent line segments. The method would also be independent of the number of line segments making up the arc or circle provided that all the mid-point normals past through the same point in space.

Bob