Wednesday, 29 August 2018

Creating Swept Blends in Revit Mass - CME Part 5

Part 5 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, and Sweeps in the CME.  Next up is Swept Blends:

Part 5:  Swept Blends

Creating a Swept Blend in the Conceptual Massing Environment. . . .

  • A swept blend requires two or more profiles, each perpendicular to the path ;
  • In the traditional Revit environment, a swept blend can only have two profiles;
  • Unlike a sweep, the path can only consist of one element (line, arc or curve), even if the profiles are closed;
  • Unlike a sweep, the profile cannot contain a loop within a loop (to make a hollow form);
  • The easiest way to do this is to host the profiles on points – in the example here, an arc has 3 points that define it, so they can also be used to host the profiles

  • The profiles can be model lines, reference lines or loaded 2D profile components - each method has its own advantages or disadvantages (described below) depending on how you want to modify the form later on, so there is no clear 'best method';
  • Create Form by selecting the profiles and the path
  • In this example, the profiles are the same shape, so there is a smooth transition, and you cannot even see the middle profile
  • NB. If you had just selected the profiles, Revit would decide its own path, which may not match the one you created – in which case the form would become a ‘Lofted’ shape

Edit Form

Editing behaviour differs, depending on the original profiles and path:

  • For model line profiles, you can use ‘Edit Profile’ – it will prompt you for which profile to edit, so you may need to put the form into X-Ray mode to be able to select the middle profile(s) or use wire-frame mode
  • In sketch mode you can modify the profile, or change it entirely
  • However, if you don't have the same number and type of segments in each profile, it may result in sharp edges
  • Try matching the segments in each profile, to make the transitions smooth, without edges  

  • For reference line profiles, the profiles can only be changed in size/proportion, depending on how much you can manipulate the reference lines without breaking the profile (but you cannot add segments)
  • For loaded component profiles, they can be parametrically controlled (best method), but you cannot reload a profile with a different configuration or number of segments 

 Point Hosting

  • The Autodesk help files recommend putting the profile(s) onto points hosted on the path (rather than using the points that define the path in the example above) – this has several advantages: it should give more control with moving end points and rotation

  • Unlike a sweep, when you create a form, it does not extend along the whole path – only between the first and last profile

If you adjust the path underneath, the form follows it:

If the profiles were model lines, then the lines and host points on the path are ‘consumed’, which means the host points cannot be selected or manipulated, and the model lines have limited controllability (except in edit profile sketch mode).


If the form is dissolved the model lines and points are kind of reinstated but not to exactly their original state:
  • Circles are split into semi-circles
  • Points lose their display status
For this reason, you may need to recreate or rehost the profiles after dissolving a form, and reset some properties.

Loft vs Swept Blend

The important thing to note with Swept Blends is that the path is included during the creation of the form, but does not become part of the form itself;  when the path is modified, the form changes too.
If the path is not included, the form becomes a 'Loft'. 

The inclusion of the path can be extremely useful when it comes to modifying the form - as will be seen later . . .


For more info on this, view the Youtube video:
Create a swept blend in Revit CME