Negative Volume


(John Brock) #41

I glad you found it.
As to the negative volume, that is completely valid from a NURBS surface modeling point of view. Certainly it is not useful for your hull modeling application.

By way of example, here are three rail sweeps using identical circle rails and a line profile.
I’ve set the backface color in the display mode to be magenta.
The one of the left has a negative volume, the one in the center has a positive volume, and the one on the right has a volume of zero.
All three are valid surfaces from a NURBS surface modeling point of view:

image

Clearly, only the center example is of use for modeling real world objects,


(IVELIN PEYCHEV) #42

Negative Volume should not exist John.

This is a programmer error. Even the one on the left the volume should be Infinity - (minus) the volume of the cylinder and not a negative volume of the cylinder.

I still believe you need to log this as an issue and get it fixed. Let the devs make it Abs(negative volume) or something.

As I said that negative value prevented Hydrostatics to calculate stuff properly. This is a serious issue.


#43

Ivelin, it is not the negative math that is wrong, but rather your negavtive attitude… :wink:
IF you read up on the math you’ll discover that nurbs can and shall produce negative values even for something (as abstract from a mathematical point of view) as the definition “volume”.

But of course in an environment where the math is used to simulate and/or predict physics then it would make sense to pop up a warning, explaining that the math returned a value that probably is useless for the user due to a modelling error.


(IVELIN PEYCHEV) #44

@Holo,

Negative volumes DO NOT EXIST, period!

Math of NURBS do not consider the positive infinite volume surrounding them. If the negative value of a volume is passed to the user then it is programming error.

It is not negative attitude it is realism and reliability of the software. It could be done in such a way that in case where two domains of the solid are created the volume is a sum of the volumes of the domains or abs(negative volume) either way this requires a fix.


#45

Sure they do. It’s a positive volume in the mirrored parallel universe to ours. Which, by the way has a left-hand-rule coordinate system, which seems to be appreciated by boat designers:stuck_out_tongue_winking_eye:


(IVELIN PEYCHEV) #46

It is not the “boat” designers that are the opposite!

Oh by the way here we should mention the ridiculous orientation of the ship in US and former USSR where Origin of the ship was it’s fore perpendicular. :wink: as if the ship would move backwards along the X axis or forward towards the negative (-X) direction. Ridiculous in my opinion.

As ridicuouls as having depths as positive Z.

(I have to mention here that Rhino’s current coordinate system orientation is exactly as I have been thaught the Ship should be oriented in space. (+X = Fore, +Y = Port, +Z - UP))

As for this I’ll accept it when I see proof.


#47

In real life, no, neither does objects without volumes, like single surfaced, open objects, or any nurbs object that isn’t joined into a flawless solid. So the boat on your monitor is only mathematically defined surfaces that can be interpreted as joined into a closed volume, or an open polysurface if you don’t model both sides of the steel. And the moment a surface is lacking or a surface is twisting into and through it self it breaks the laws of physics and thus should in your world return a big fat VOLUME IS FALSE BECAUSE YOU MODELLED THIS WRONG YOU NOOB! error. :smiley: But Rhino doesn’t do that. Instead it tries to give you a most accurate volume calculation based on what you handed to it in the first place.

I have many times appreciated the estimated volume from crap models before spending the extra time on the final production part.

That I agree on. And giving sensible feedback when a user has accidentally done something wrong, or if the computer has messed up is called “Good UX” which is always important imo. At least when the user is close to a deadline.

Peace and cheers! Off to grab a beer.


#48

Have a little faith, baby…!


(IVELIN PEYCHEV) #49

Negative volume is more wrong than infinitely large or infinitely small volume. You’re wrong again!

That said,

The reason one would think single surfaced, open objects or non-joined nurbs have no volume is because it’s infinitely large (in case of single object) and infinite number of infinitely large volumes in case of non joined polysurfaces.

even so all of these are positive volumes close to + infinity or infinitely small close to 0 (zero).

I did nothing wrong as these surfaces exist and hydrostatics of them is calculated and on such draft the ship would not displace NEGATIVE VOLUME OF WATER. OMG!


(IVELIN PEYCHEV) #50

I have more faith in someone discovering Negative Gravity than discovering Negative Volume!