Negative Volume

(John Brock) #21

Sorry, I don’t understand.


Nurbs can be retrieved by untrimming them.

How can I trim nurbs but noone being able to retrieve the original one (the untrimmed one)

Meanwhile GH also calculates negative volume


(John Brock) #23

If you mean is there a way to “lock” your surfaces so I can’t edit them, no there is no way to do that.
Locking would make it so I couldn’t figure out what was wrong either.

I don’t do Grasshopper at all, but given your polysurface, I’m confident I can figure out the problem, or identify a bug I can get sent off to the developers.

You would need to trust us that we would not share your file outside of Rhino development.


So…?? How do you expect them to help if you don’t send the file? Obviously it’s not a common problem, it’s the first time in 20 years I’ve ever heard of it, they need the bloody file. They’re not going steal your design, it’s their job to support their customers. Don’t post it here if it’s confidential, obviously.



why are you even posting?!

If the McNeel support was private not public I would’ve already sent the file. Stay out of this conversation would you?!

The problem is that the model is not mine, I rev engineer it for a customer, it is theirs not mine.


(John Brock) #26

The discussion forum is public
Messages sent to are private.


As I said I’ll need to ask for a permission before sending the file.

The reason for this thread was:

  1. for you to log it.
  2. to bounce ideas to see if I can find the issue myself.

(John Brock) #28

It sounds to me like that’s exactly what has happened.
You tried my ideas and they didn’t work.
Now I need the file.



I appreciate that John.

I hope anyone has some other idea I can test.


Joining the surfaces inside GH also leads to negative volume


(John Brock) #31

If you can get permission to send the file, or if you can modify that one enough to obscure the design but still have the error, please send it to describing the problem.



Good idea

(Luis Fraguada) #33

I think if you run _shrink or similar (sorry, posing from phone) it shrinks the trimmed NURBS, effectively destroying the original srf.


Thanks for the idea Luis,

It shrank only the planar surfaces.

(Luis Fraguada) #35

Sorry, I think it’s _ShrinkTrimmedSrf


yes, that one. It appears if there’s a curved edge in that surface the control points extend beyond the trimmed edge. Even after it is shrunk.

(Luis Fraguada) #37

Yes. It does it’s best to create a NURBS representation that is the minimum to not affect the trim.


Did you stack any control points when making the surfaces? That was often a problem with MaxSurf as that was how they made hard chines and when imported into Rhino the resulting ‘degenerate’ surface would do all sorts of weird things.


the only stacked control points are at the edges between two surfaces so I can match the curve. Other than that none. That’s why I said above that I am aware of each point’s location and there are no self-overlapping surfaces.


We have a winner! :man_facepalming::1st_place_medal::trophy::sunglasses:

What a coincidence water plane cuts the surface in such a way that creates two domains of the solid, which I think is the reason to result in a negative volume. That prevented Hydrostatics from calculating two of the parameters properly.

Still though some warning should pop-up instead of making a volume negative value.