Thursday, June 27, 2013


Almost 2 years ago now I attempted to make a big lumpy diagrad roof surface.  Very large scale structure, shades of Bucky Fuller.  Shades is right because it was essentially an enormous shade structure.

I got stuck at some point and since this was an inquiry "after the fact" it's been sitting neglected ever since.  It related to a quick competition entry & the inquiry was basically, could we have done this more easily using Revit ?  One of the interesting things here is the realisation that 2 years ago I was floundering about as far as conceptual massing was concerned.  The big breakthrough for me came with the first pumkin competition a few months after this initial failed attempt.  So I decided to take another shot.

My first instinct was to make a rippled rectangular surface and cut off the edges with voids.  That didn't work.  Or rather it seemed to be working until I divided the surface.  Then it just ignored the voids & reverted to dividing the full rectangle.  (SEE ALFREDO'S COMMENT below, pointing out that it IS possible to select the inner surface, you just have to KEEP ON TABBING)

I found that I could bring the surface into a project and use curtain system by face.  But that only allows me to use rectangular panels.  I wanted a rhomboid. So I decided to drop the void idea and try to make the surface directly.  ie a lumpy-bumpy surface with a smooth irregular outline.

This turned out to be fairly easy, in principle at least.  Just a series of splines like before, but instead of lining the ends up, let them move in and out with the boundary curve.  Make the first and last curve shorter and push the mid-points out so that the curve in plan.  With a bit of pushing and pulling you can create something with flowing curves in both plan & elevation.

Now for the next problem.  The divided surface distorts to in response to the irregular border.  Not to worry, divide by intersects to the rescue.

This takes a little while to set up.  Lots of reference planes.  But it works.  So let's try to build something closer to the original shape.

I quite enjoyed using this method for defining a surface on the second time around.  The curves are simpler and I'm getting better at bending the shape to my will.  I didn't get around to setting all the intersect planes up though.  Time ran out on me.

Maybe that's just as well, because when I started on this little write-up it struck me that my surface cut by voids might be solved by having a solid cut by voids.  In other words, take the open ended splines and box them out so they each form a closed loop.  Now when I select these and create form I get a solid block with a wavy top surface.  Cut this with the voids I made before.  Now I can select the top surface and divide it.  Works fine.

This is preferable to the intersects method.  I can play around with the density and angles of the rhomboid grid just by varying the U & V values.  Also, changing the boundary shape in plan is going to be simpler.  What is more, I suddenly realise that I can use loaded profiles threaded on a spline for the solid.  Pumpkin take 2 comes into play.  Organic form and all that.

So I make a profile by my usual points method, building in a bit of parametrics.

Set up a spline for the backbone of the whale, or maybe it's some kind of a manta-ray type beastie.

Thread the profiles along.  And make a form.  Tweak it a bit.  Looking good.

Go into plan view and set up the reference line loops for my 2 voids.  Make them as solids first, then switch to void and cut geometry.  Nice.

Now tab-select to get the surface.  Divide it.  Interesting how the grid lines follow the curvature of the backbone.  Switch to romboid & tweak the U V values.  Load up a panel and we're in business.

So what did I learn ?

  • You can trim a surface to shape, but when you try to divide it ... it reverts to the original.
  • You can model a surface directly with smooth flowing edges, but when you divide it the grid will follow the  edges.
  • To place an even grid over an amoeba-like form, make solid geometry & tab select a surface to divide.  The more rectangular the original shape (before edge cutting) the more regular the divided grid.

and finally :  Keep trying because there is a way to get the effect you are looking for.


  1. A surface that has been cut with a void can be divided. The trick is to select it in a certain way. If you hover the mouse over the surface that has been cut, (without a click) the lower left corner of the screen will show "Form element". Now hit the TAB key. Now it says "Joined solid geometry". Now hit the TAB key. Now it says "Joined geometry: face". Now click. Eureka! Now you can divide the surface, and apply the rhomboid pattern to the surface that had been cut with voids.

  2. Thanks Alfredo. Obviously I didn't persist long enough in my tabbing. Not to worry, as usual my shortcomings led me down another path or two which proved interesting & potentially useful. But it's good to know that surfaces can be cut AND divided.

  3. Your blog posts just tackle my current needs. I need to sit with you one day Andy.I am trying to do same kind of thing for manufacturing ceilings and I am still wondering in Conceptual environment to get exactly what I want...

  4. No problem Arsen, give me a call some time.


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