Friday, March 25, 2022


Is AI good or bad? Do lock-downs work? Have we forgotten how to do nuanced risk-benefit analysis?

It's easy to criticise Putin if you live in the Western Quarter of the Global Village, but harder to query the dominant narrative about other topics. How could you possibly speak up for Fossil Fuel or Nuclear Energy? Why express reservations about the runaway train of Diversity Worship?


As a painter, musician, designer, I face the challenge of navigating a route between variety and cohesion.  I value diversity, but I also value its opposite.  My task as an artist is to strike a delicate balance. But what about public life in a typical “liberal democracy”?  Is a balanced view even possible? How can we swim in the frenzied currents of polarised politics, torn between the opposing poles of "woke activist" and "right wing bigot”?  Words become weapons, their meanings carefully framed. 

Why would we want to “Capture” Reality? What would the polar opposite approach to this be?  I like to think of my BIM pencil work as "Releasing Reality," not enslaving it: like Michelangelo, liberating his statue of David, trapped inside a block of marble. The tunnel vision approach of reproducing the surface appearance of "Heritage Buildings" does have some value of course, but I worry that it obscures the deeper vision of a search for meaning by means of analytical studies. 


So, I stumbled into this modelling query on Linked-In.  It’s a lighthouse.  Beacon of light to save mariners from floundering on the rocks.  How do you persuade a sweep to wrap itself diagonally around a cylinder?  “That’s why we don’t use Revit” opined one voice.  You’ve got to love engineers.

I remembered a post I did many years ago, (2013 in fact)



So I created a cylinder and cut it with a diagonal void.  Now you can use “pick-edge” to create a path for the sweep that will represent one of the diagonal mullions.  



Now I remember why I used a circular profile in that old post.  Call it the “twisting problem”  You can’t get both ends of the sweep to penetrate the cylinder at right angles. 



Even worse, when you create a radial array the angles twist further around as the array progresses.  I guess they are all trying to relate back to the original edge that gave birth to their sibling.  Something like that.

Issue no 1 can be tackled by using a swept blend.  Now you have two rotation parameters.  Give them different values to maintain the relationship from top to bottom of that first diagonal mullion.  It almost works. 

Unfortunately, as the difference between the two angles increases there comes a point where the vertices jump their connections.  Now the short side is morphing into the long side.  It’s very weird and difficult to capture in a screen shot.


Now in a simple “Blend” you have an option called “Vertex Connect” which is quite cute. You can do a manual over-ride to tell Revit which corner connects to which.  I had never looked for this in a “Swept Blend” before.  But there it is!  Wonderful.  And there’s a quick fix using “Twist Left” or “Twist Right”. 


The second issue is solved by saving a single diagonal mullion as a standalone family and then nesting it back into a second family before creating the array.  Much more stable.  The path takes its host edge from the nested family. The array process in the host doesn’t filter down to affect work-planes in the nested level.

I need the mullions to start and stop neatly at a horizontal band at the top and the bottom of the glazing.  So I create a cylinder in the mullion family (set to invisible) and eight vertical lines (also invisible) around the edge.  While editing the swept blend, you can drag the end points of the path.  It will remember the curve of the original edge, even if that geometry was deleted.  But you can manipulate the length.  So now I can get the mullion to go from the base of one line to the intersection with the “next but one.”  In other words it’s doing a quarter turn (90 degrees)


It soon becomes obvious that the height of the glass needs to be equal to the length of the chord of this angle.  You can get this by Pythagoras or Trigonometry, but I just drew it in plan and set the height to the nearest millimetre.  Now you can fine tune the end angles to stop and start in a horizontal plane (check this in elevation)

I did the glass as a continuous thin-walled tube, but there are only two sizes, (three if you count the upside-down triangles as different) So it should be easy enough to create the individual panes as nested components also.  I guess you could figure out how to make the whole thing highly parametric so you can type in whatever size and proportions you need.  I think I will rest where I am though



An interesting exercise.  Learnt something new about swept blends. Brought back memories from almost a decade ago.  Reminded myself that democracy, for all its faults and frustrations is a beacon of light to the world’s floundering ships of state … 

if only it can recover its self-belief !

family link below. just one way of doing it.

Lighthouse 04.rfa




1 comment:

  1. Thank you for sharing. Many times, I know what I want to do and don't know the tools well enough to know which to use.


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