Saturday, June 29, 2019


A second Recap post, hopefully bringing us up to date. Here I am talking about where we were 3 or 4 weeks ago. 

Around this time, Alfredo was working out his approach to modelling the complex arrangement of vaults around the curve of the apse at the East end of Notre Dame.  That was quite a challenge and generated a lot of discussion, especially the vaulting of the triangular sections which result in a kind of zig-zag arrangement. 

In the last post I mentioned our exploration of models on Sketchfab related to Notre Dame. More power to everyone who has had a go, whatever the software used or the reason for taking on the challenge. I’m sure you all learnt a lot along the way, and nothing said below should be taken as criticism. They are all worthy attempts in my view.

However, it does seem to me that mesh models tend to focus the mind on surface detail, and don’t lead to the kind of structural questioning that a BIM approach stimulates. 

Common mistakes include 1) failing to notice that the Triforium galleries turn the corner at the Transepts, and 2) over-simplifying the rhythm of buttresses and window bays around the curve of the apse. In my view the simple fact of flipping between a 3d window and plan/section views (complete with grids and dimensions) makes a BIM approach much more likely to reveal subtleties of design such as the two I mentioned above. BIM forces you to think more carefully about how a building is built, how walls line up on successive stories, where staircases lead, etc.

There are some interesting models on Sketchfab, and I have found the ones based on photogrammetry especially useful. I got a bit carried away taking screenshots for future reference. It’s useful to flip through these, but nothing beats orbiting around the source model.  Important also to find a balance between active modelling and close study of the reference material.

So back to modelling. I noticed that the round columns were displaying inconsistently, and some had a wide slot cut out of one side.  They were nested inside arch families and “join geometry” was causing problems. Ultimately, I am inclined to dispense with nested columns completely and place individual columns directly. Sometimes you can try to be too clever for your own good.  Notice how some of the columns are displaying as if viewed from above, rather than sliced by the cut-plane.


I decided to tackle the four columns at the corners of the crossing. For some reason the East walls of the transepts are treated rather differently from the West Side. The two columns on the West Side are treated simply with flat faces, while the two to the East are expressed as bundles of ribs. Is this just a whim? Does it express the richness of the chancel in contrast to the nave, where the common people sit?  I know not, but they are interesting questions.

A lot of fine tuning and elaboration needed down the line, but my current focus is looking for misconceptions and anomalies, places where “first pass” modelling is still required.  Ideally, we want to keep everything at the same level of development and resolve issues that arise before jumping ahead to add more levels of detail.  It certainly would help to have access to a point cloud. 

Next, I set about adjusting the Triforium arch down the sides of the nave.  I placed a jpeg behind a semi-transparent section view to act as a guide while I adjusted the proportions. It won’t be the last time I revisit this family, but I’m comfortable with the progress made on this occasion.  Just need to do a similar exercise for the smaller arches around the chancel.

Back to the round columns again, and I realised that there are several different versions, even before you get to the variations in capital style. So I tackled two of these, one with big bumps on the side, the other a tight bundle of ribs. The 4 bumps version is a one off close to the West End, adjacent to the nave.

The ribbed version occurs alternately between the two aisles. Again, I’m comfortable with the progress made in this area for the moment. Maybe next on the list will be side chapels, which are extremely bare at the moment.  But meanwhile, exchanges with Daniel and Marcel set me off upgrading the Site Context link. 

Marcel picked up some 3d geometry from a site called… and after some discussion and experiment we found that by bringing it into Revit via Sketchup we obtained an explodable object that became a series of solids, so that we could delete the crude representation of the cathedral itself.

What we have now is a combination of those solids, some of the Revit geometry I had created previously to represent the river, and a bit of extra modelling in Revit to plug some gaps. 

More recently I spent a weekend tackling the end walls of the Transepts. These are remarkably complex compositions with all kinds of passages, spiral stairs and access galleries that I am still struggling to understand. But once again it feels good to make some significant progress, even though I know there is a long way yet to go.

Since then Alfredo has contributed a detailed model of the Rose window. 

This project is a voyage of discovery.  It’s all about learning, digging deep, striving to understand.  Collaborative BIM is a wonderful tool for exploring history, how things work, why buildings are designed the way they are.

Early on, we discovered that the triforium galleries “turn the corner” at the transepts… something that many other models have missed.  But another surprise was lurking.  One of these returns pops up in the corner.  Why?  Maybe it’s just a way of introducing a taller window at the end.  I suspect it is one of the novelties introduced by Viollet le Duc.  BIM helps us to ask penetrating questions and we have much still to learn.


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