Creating Lofts in Revit Mass - CME Part 6

Here is part 6 of my series on  comparing the five traditional form creation tools with equivalent techniques in the Revit Conceptual Massing Environment.
Previously we analysed the creation of extrusion forms, Blends, Revolves, Sweeps and Swept Blends in the CME.  Hang on - part 6 of 5?  Oh that's right, there is no way to create 'Loft' forms in the traditional Revit environment:

Part 6:  Lofts

It is possible to create a 'Loft' in the Conceptual Massing Environment - it is a little different to a Swept Blend, and has its own rules (and problems).  A loft is a 3D form made by linking a series of planar profiles to create a surface(s), which can be flat, faceted, curved or double-curved (NURBS).  I consider a loft to have a minimum of 3 profiles, as 2 would just be a 'Blend'.  The profiles are linked along a notional path - the difference between this and a Swept Blend is that the latter uses a specific path element, and a loft does not.  Revit will figure out its own path (or not, as the case may be!).

As soon as the edges are not aligned and you have 3 or more profiles, you will get curved surfaces – Revit creates its own spline edges.

The greater the displacement between profiles, the more dramatic the curves

The profiles do not have to be parallel to each other, but as soon as they are at different angles it becomes less predictable as to whether Revit will create the form as you desired. In the example below, the profiles were hosted on reference planes, which can be rotated, but only before the ‘Create Form’ process

Revit may not create the form at all, and you might get this error message:

If the error mentions 'Self-intersecting geometry', it may be due to Revit getting the profile order wrong such that it tries to create a form that doubles back or crosses over itself - something that Revit does not like one little bit.  When you select the profiles in the first place, it makes no difference which order you select them - you have absolutely no control over the order that Revit uses in the Create Form function.  It is not clear how Revit decides on the order - it may be proximity to each other?  However, I don't think it is that simple.

The second part of the error message talks about the 'Reorder Profiles' button - this is not usually visibly apparent.  There is a blank space for it in the bottom left corner of the dialog box.  Wouldn't it be nice if Revit tried to Create Form again with a different profile order;  better still if it asked you to nominate the order!

About once in every few hundred times you get this dialog box, there will actually be a 'Reorder Profiles' button.  Be very careful about clicking on it.  The first time I tried that, Revit crashed out and closed without saving anything.  Thus it is wise to save all files before attempting this.

If you do click on the button, it won't help!  If it doesn't crash, it will just fail again.  It would seem that one of the programmers was aware of this form non-creation ability of Revit, and they tried to add a solution.  However, it seems like this functionality was removed from Revit before it was released to the unsuspecting public.  Sadly one instance of the many variations to the dialog box still has the button there to tantalise us.

If you would like Autodesk to fix this, please go to the Revit Ideas wishlist and vote for this enhancement request:

Control profile order during form creation


This description of Loft creation shows a very simple example - it can get quite complex.  There are many tips and tricks as to how to make Loft form creation easier and more predictable in Revit.  More to follow later . . . .

Creating Sweeps in Revit Mass - CME Part 4

Part 4 of my series on  comparing the five traditional form creation tools with equivalent techniques in the Revit Conceptual Massing Environment.
Previously we analysed the creation of extrusion forms, Blends and Revolves in the CME.  Now  we sweep on to the next form:

Part 4:  Sweeps

 Creating a Sweep in the Conceptual Massing Environment has a few unexpected rules and exceptions - some of which you can use to your advantage.

• First you have to create a path for the sweep, consisting of one or more chained lines, arcs or curves (model or reference) - this is one of the few occasions that you can have multiple element segments to a path in the conceptual massing environment (if not the only one).
• Then create a profile that is perpendicular to the element of the sweep that it intersects.  

 

• NB. If the profile is open, Revit only allows a single element for the path

• You can place the profile on a convenient perpendicular work plane but the easiest and most reliable way to do this is to host a point on the path then host the profile on the point (set the point reference as work plane) - as recommended by Autodesk.

• Select the profile and path; 
• Create form 
• It should create the sweep

• However, it may give a message ‘Unable to create form due to self-intersecting geometry’

• The most common reason might be if you have arcs/curves on the path where the radius is too small to make the transition between straight sections on the inside, as in the example below where the middle arc radius is very close to failing – two profiles are almost meeting each other on the inside of the corner

• To avoid this problem you could make the path radius larger than required to start with, then reduce it afterwards so that you can see where any problems occur; alternatively, make the profile smaller, then increase it after the form is created - check in X-Ray mode to see where profiles may be close to intersecting. 

• To edit the path or profile:
  • If the profile was made from model or reference lines, it can be edited in sketch mode using ‘Edit Profile’ once any part of the form is selected;
• The path (model or reference lines), can be edited in sketch mode – in a very limited fashion, eg. changing the radius of an arc; in this case you may need to use the X-Ray mode to be able to see the path to select it.

Hollow Sweep (Nested Profiles)

In the Traditional modelling environment, Revit usually allows you to have nested loops within a profile in order to create a hollow form.  The Conceptual Massing Environment is less forgiving - I have only found two situations where it is allowed:  One is Revolves and the other is:

• Revit does allow a profile with a loop inside a loop, but only if the profile is made from lines/arcs – not from a loaded family profile;
• You could offset/copy the original profile (or draw a new inner loop profile) 
• Select both profiles and the path elements
• Create form
• Hopefully it will create a hollow form 
• It will show joint lines for each segment of the path

• If you want to use a loaded family as the profile, It does not allow you to create a hollow form in one command:
• You need to create two separate forms, one solid and one void;

• In this situation, it is best to keep the path as reference lines, so that they can be used for both forms;

• Select the path plus outer profile;

• Create the solid form

• Make it X-Ray so that you can see and select the path and the inner profile

• Select the inner profile and the path
• Create Void Form

• It should cut the void from the solid automatically

• Interestingly the combined form does not show any joint lines (where transitions are tangential) – this is desirable in the project

Joint Lines

• Prior to seeing this result, I tried hiding the joint lines in the project by putting them into a subcategory or associating a visibility parameter but that affected the whole form, not just the joint lines.

• Making the original profile a reference line does not hide the joint lines either

• It looks like we may have to create combined solids just to solve this.

Youtube

Youtube links for those who don't like reading:   Create a sweep in CME