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Why does the "Create Form" command allow to create a surface with some selection and not with other?

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Nachricht 1 von 13
stefanome
2500 Aufrufe, 12 Antworten

Why does the "Create Form" command allow to create a surface with some selection and not with other?

I would like to understand why Revit sometimes allows to create surfaces and sometimes it doesn't.

 

The following steps show that selecting a closed loop of curves may or may not allow to create a bounded plane. Can you please help me understand when to expect what behavior?

  • I created a new mass in place.
  • Then created a line and a spline to define a closed loop, then a rectangle to define a second closed loop.
  • Then I selected the line and the spline, clicked on "Create Form", and had the option to create either an extruded closed solid or a surface (an open solid with one face). I created the surface.
  • Then I selected the 4 lines, clicked on "Create Form", and an extruded closed solid has been created without giving me the option to create a surface.
  • Then I selected the surface created with the line and the spline, clicked on "Edit Profile", deleted the line and the spline, created a rectangle, and ended up with a rectangular surface.

stefanomenci_0-1616423605522.png

Is there another way to create a rectangular face, other than modifying the profile of a surface created with another profile that Revit happened to like?

12 ANTWORTEN 12
Nachricht 2 von 13
stefanome
als Antwort auf: stefanome

I found just another behavior, more and more inconsistent and unpredictable and difficult to learn: I created a 3rd shape using 3 lines and 1 reference line. In this case I had the option to create either surface or solid. I created the surface, then selected the surface and found out that the "Edit Profile" option is not available.

Why is the "Edit Profile" available in some cases and not in others?
Nachricht 3 von 13
barthbradley
als Antwort auf: stefanome

Nachricht 4 von 13
stefanome
als Antwort auf: barthbradley

That video has nothing to do with my question.

Nachricht 5 von 13
barthbradley
als Antwort auf: stefanome


@stefanome wrote:

That video has nothing to do with my question.


 

I thought it did. You asked if there was another way to create a rectangular form.  

 

Mass Rectangular 1.jpgMass Rectangular 2.jpgMass Rectangular 3.jpg

 

Nachricht 6 von 13
stefanome
als Antwort auf: barthbradley


I thought it did. You asked if there was another way to create a rectangular form.  

Well, I actually asked why I can create a surface with one profile and not with another, I wasn't interested on the rectangular form, I was interested in the profile, whatever its shape was (sorry, I didn't specify this detail).

 

I knew it was possible because I had seen those two buttons that ask you whether you want to create a surface or an extrusion, but I didn't remember in what context. So I tried with all types of masses and families and templates and environments, but I couldn't find it. Then I tried with all combinations of entities and I found out that making a rectangle and creating a form doesn't allow to create a surface, but making a rectangle, deleting a line, adding a spline and creating the form does allow it. Then it is possible to select the surface, edit the profile, delete the spline, create the line, get back the original rectangle and the rectangular surface bounded by a profile finally works. All of this apparently makes sense in the Revit world, but it doesn't make any sense to me. Hence this post.

 

It is difficult to learn the Revit way when you don't understand why Revit decides to allow you to do something or not.

 

Here is a little background on why I am asking this question:

 

My goal is to create one family containing many surfaces, each with its own profile, so I can click on the family, then edit family, then click on one face, then edit profile. The faces represent a sheet metal panel that typically has 5 faces, but it can range anywhere between 1 and 30+ faces.

 

The attached model shows a very simple example that I was able to create using the insane put-the-spline / delete-the-spline trick.

 

This little model is a proof of concept to study the feasibility of an add-in that I am planning to create. The add-in will create thousands of panels using this technique. I want the panels generated by this add-in to be:

  • Light weight (hence the surfaces generated by one single profile that takes care of all the notches rather than closed solids with many voids; voids will only be used for slots)
  • Easy to generate by my APIs (I hope that if I can create a shape and a face using the UI, I can do it also using the APIs)
  • Easy to modify by the user if they need some custom changes (if a panel needs some cut out that the add-in can't foresee, the user must be able to right click and edit the profile)
Nachricht 7 von 13
barthbradley
als Antwort auf: stefanome

...so you're a sheet metal fabricator in a Revit world.  How's that working out for you? 

Nachricht 8 von 13
stefanome
als Antwort auf: barthbradley

I know, right?

 

I am trying to avoid doing the job twice: lots of info is already in the Revit model, I want to avoid duplicating it to another tool like Autocad or Inventor and going back and forth between two environments. If I can write some code and teach Revit a few new tricks, I might be lucky and get Revit to manage the whole process.

 

I'll let you know in 6 months.

Nachricht 9 von 13
constantin.stroescu
als Antwort auf: stefanome

  • basically when you use as Work Plane a Level or a Face of an object , Revit will think that you want to create an extruded Form having as components the Profile ( placed on that Work Plane) and direction of extrusion the Normal (Vector) on this plane., thus and Extrusion
  • When you create a Chain of Lines using 3d Snapping ( this can be a planar if 3 points or multiple planar, usually when more than 3 points), Revit can not decide what to do , so is up to you to do it...Do you want to create a surface ( could be a Polysurfaces) or Extrusions Normal on these surfaces?

Image 5.png

Constantin Stroescu

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Nachricht 10 von 13
stefanome
als Antwort auf: constantin.stroescu



I don't follow your explanation. I still see two sets of input virtually identical to each other producing different results.

 

@constantin.stroescu wrote:

Revit can not decide what to do


What do you mean "can not decide"?

 

What is the difference in the input between 4 lines laying on a plane and 3 lines plus a spline laying on the same plane?

 

The input in both cases is a set of planar entities laying on the same plane, but in one case Revit decides that I want to do a closed solid, while in the other case it asks me.

Nachricht 11 von 13
constantin.stroescu
als Antwort auf: stefanome

See if you use

  • a Spline with Control Points ( 2d) - it will not ask you what you want to do , Revit will make an Extrusion- 
  • and if you use Spline Through Points -( 3d -that creates a 3D Spline that use 3 points)  - introducing a 3d entity , Revit will need some extra information.

Image 6.png

Constantin Stroescu

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Nachricht 12 von 13
stefanome
als Antwort auf: stefanome

Now I understand why sometimes Revit allows to create a surface and sometimes doesn't. As you say, when the spline has been created with one button rather than with the other.

 

I marked your answer as the accepted solution, because it does describe the behavior that I didn't understand... but I still don't understand the reason why Revit has been designed in such a way.

 

I will try to express why I am still confused. Here are the things in my mind right now:

  • No CAD in the world (well, the ones I used) considers splines with control points 2D and with interpolation points 3D
  • Not even Revit. Indeed you can create a so called 2D spline, extrude it, pick an edge of the form, pick one control point and drag it out of its plane. Now the 2D control point spline is not planar (see snapshots below)
  • A spline through coplanar interpolation points is planar, but Revit calls it 3D
  • Even pinching my nose and pretending that the definition of 2D and 3D splines makes sense, why am I allowed to create a surface out of coplanar curves containing a 3D spline and not out of coplanar curves not containing 3D splines? In other words, if Revit was designed to work this way, there must be a reason why they decided that two sets of coplanar curves must give different results, depending on the button used to create them. What is this reason? (The reasoning that lead to create a command that behaves this way, not the description of the command).

With my limited knowledge of Revit I can't understand why. Perhaps they are trying to guide the user to do the right thing and ask them to do acrobatics like add-a-spline/create-a-surface/replace-the-spline-with-a-line to the less right thing? If this is the case, what are the right things you do with Revit vs the not right things?

stefanomenci_0-1616623972436.png

stefanomenci_1-1616623976638.png

 

 

Nachricht 13 von 13
constantin.stroescu
als Antwort auf: stefanome

Perhaps they are trying to guide the user to do the right thing and ask them to do acrobatics like add-a-spline/create-a-surface/replace-the-spline-with-a-line to the less right thing

 

I agree with you...

Basically Revit is a BIM instrument and it is developed so to work with AEC entities , to create a Virtual Building, to facilitate an advanced level of collaboration while the design process , to prepare the Model to be used further into Construction and Exploitation phases.

The 3D Mass Modeling level can not be compared with other dedicated 3d Modeling Softwares that are designed to work with NURBS and NURMS. 

In fact Mass modeling of Revit has as main purpose to create building envelopes  that are used for simple preliminary studies, volume and Gross Area reports, energy analysis ....all pragmatic purposes.

So , yes , Revit has some predefined settings and try to anticipate your design needs. 

As a MAX user, for instance,  you will be disappointed  by the degree of how Revit works at Sub-object level, or with Material mapping ...

But for building design process Revit is an excellent tool.

Constantin Stroescu

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