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