topic Re: Creating an elliptical hemisphere in GDL

Creating an elliptical hemisphere

minami — Thu, 26 Sep 2024 11:57:08 GMT

Is it possible to create an elliptical hemisphere like the image with GDL commands?
If so, what command should I use?

Re: Creating an elliptical hemisphere

Barry Kelly — Fri, 29 Sep 2023 06:37:32 GMT

You could use a SPHERE and cut it in half.

Or better still there is an ELLIPS command that is half a sphere where you can control the height independent of the radius.

But in either case to elongate one axis, you will need to use the MUL command.

Barry.

Re: Creating an elliptical hemisphere

Lingwisyer — Fri, 29 Sep 2023 07:31:37 GMT

For the shape presented, ELLIPS would not work as that would create tangents along the cut rather than a Spherical Cap.

For the presented shape 3 variables would need to be defined. R1 you circles radius, R2 to distort it using MUL and H, used in conjunction with R1 to calculate R3, your spheres radius.

R3 = ( R1^2 + H^2 ) / 2H

With R3 in hand, you can then subtract H to set your CUTPLANE. OR better, offset your sphere into your cutplane.

Ling.

ps. Curious what would require such a shape... something that requires an object to be scripted...

Re: Creating an elliptical hemisphere

DGSketcher — Fri, 29 Sep 2023 10:52:45 GMT

If you don't want to use GDL an alternative would be to use the Shell tool.

Basically you would draw a half ellipse and rotate it around the long axis by 180 degrees.

Re: Creating an elliptical hemisphere

Barry Kelly — Fri, 29 Sep 2023 11:40:58 GMT

Or just use the 'ellipsoid' primitive shape object in the default library.

It even has a cutting plan for half an ellipsoid.

Barry.

Re: Creating an elliptical hemisphere

DGSketcher — Fri, 29 Sep 2023 12:37:16 GMT

🤔 I can't believe the primitives are localised but I'm not seeing that split option in the UKI library...

Re: Creating an elliptical hemisphere

Barry Kelly — Sun, 01 Oct 2023 10:33:27 GMT

I only have 22 open at the moment.

This is what I see (AUS library).

Unless it has changed in later versions?

Barry.

Re: Creating an elliptical hemisphere

Barry Kelly — Sun, 01 Oct 2023 10:45:04 GMT

I just checked 26 and no there is no cutting plane option or hollow shell.

Why do they take options away?

There is a semi-sphere object, but you can not stretch it.

That ellipsoid I have in 22 may even be from an older library still.

It has no license restrictions or author information I can see, so I have attached it here.

Barry.

Re: Creating an elliptical hemisphere

Lingwisyer — Mon, 02 Oct 2023 01:49:14 GMT

Yep, Ellipsoid 22 does not have the option...

Re: Creating an elliptical hemisphere

Barry Kelly — Mon, 02 Oct 2023 02:30:26 GMT

I checked out the origin of that object I posted and it looks like it is from version 10.

It seems newer amended objects are not always better (did someone say 'cabinets' ? )

Barry.

Re: Creating an elliptical hemisphere

minami — Mon, 02 Oct 2023 02:56:02 GMT

I will refer to the GDL I received.
thank you.