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

Thursday, 19 July 2018

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