Reparametarizing the surface in Grasshopper

Either I am doing something wrong, or I do not understand the concept on which Grasshopper works.

I wanted to subdivide the surface into segments. I draw two curves in Rhino, and the rest of the process I did in Grasshopper (Loft, dividing the surface, and exploding).
The problem is that, surface is not divided evenly, like it was not parameterize. Even though it is. Take a look:

Then I tried a different solution:

I made the surface in Rhino, out of the same curves like in previous example, reparameterized it in Rhino, and then divided in Grasshopper and exploded.

For some reason, this solution worked perfectly, and surface is now divided evenly. Take a look:

Does anyone know, why is the first solution not working?

Thank you.

Replies to This Discussion

Permalink Reply by David Rutten on July 15, 2012 at 9:39am

Reparameterization is not going to do anything in this context. All it does is change the domain of a surface, not how slowly/quickly the parameters change across the surface. If you want to change the progression of parameter (or "parameter density" if you will) you need to rebuild the surface, which unfortunately changes the shape.

Are you certain that your loft options were the same in Grasshopper and Rhino?

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by djordje on July 15, 2012 at 9:52am

I am not certain if the loft options are the same David.

Here are the files:

Attachments:

reparameterize surface.3dm, 47 KB
reparameterize surface.gh, 4 KB

Permalink Reply by David Rutten on July 15, 2012 at 11:12am

They're probably not. The loft made in Rhino isn't even close to the original curves:

See the attached file, I provide two different lofting options, one without Rebuilding one with rebuilding using 20 control points.

David Rutten

david@mcneel.com

Poprad, Slovakia

Attachments:

reparameterizesurface.gh, 3 KB

Permalink Reply by djordje on July 15, 2012 at 12:49pm

Thank you for the reply David.

But I am still having problems. Maybe the reason for this is because I am using 0.8.0066 version of Grasshopper and I can see you saved this file in 0.9.0002

When I open your file, Both of Loft options parameters - Default and Rebuild (I could not even find them in 0.8.0066. Do they even exist in that version?) have the same data in it. Take a look:

I repeat, maybe the problem is on my side, as I am using older version of Grasshopper than you. I couldn't find the download link for that 0.9.0002 version.

Permalink Reply by David Rutten on July 15, 2012 at 1:48pm

Loft Parameters are so rare that they are not available in the UI. I created those by using the "Extract Parameter" option in the Loft component input menu.

I see there's a problem with deserialization though, which may be due to file format forwards incompatibility. You cannot download 0.9.0002, I'm the only one who has it because I'm still developing it.

You're right about the Rebuild option though, None needs to be changed to Rebuild. You can also do this directly in the Loft input.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by djordje on July 15, 2012 at 2:17pm

Understood.

So from now on, I always need to rebuild my lofted surface, before using it further in the Grasshopper process.

Thank you David, as always - quick, precise and more than helpful.

Do tell me if a voting for a new CEO emerges, you have my vote :D

ups, sorry Robert, this should have gone through private message :)

Permalink Reply by Danny Boyes on July 15, 2012 at 3:19pm

So from now on, I always need to rebuild my lofted surface, before using it further in the Grasshopper process.

No. A well thought out surface constructed with well placed control points is far better than the brutal rebuild strategy.

Take the example below.

The surface closest to you is constructed by loft from curves with control points grouped closer in the bend. No Rebuild

The Yellow surface is made with a rebuild with the same number of points but as you can see in the Front Viewport it doesn't have the same shape.

In order to get a closer fit you have to have more points distributed over the entire surface just to get enough where it counts. Furthest surface has a rebuild of 25 (still not the same as before rebuild)

Permalink Reply by djordje on July 15, 2012 at 4:06pm

Thank you for the tip Danny.
How can I add those points near the bend part?

Permalink Reply by Mario L on July 15, 2012 at 10:37pm