Sunday, March 15, 2020


“Always” may be a bit too strong, but most of the time I find that work takes much longer than I originally expected.  Changing the grid for Notre Dame seemed a fairly straightforward exercise, but … it’s a complex model  AND  there have been several diversions along the way ( I do love a good diversion.)

One such detour has been my attempts to create a parametric dome family without resorting to Point World.  Alfredo has done some fantastic work using the power of adaptive components and hats off to him for this contribution to our project.  Along the way, he found Viollet-le-Duc’s dictionary, which contains some very interesting geometry analysis.  He uses a semi-circle for his diagonal ribs, and he seems also to fill in the spaces between ribs with vaults of a constant radius.  SO … Perhaps we can extract all those vault surfaces from hemispherical domes.  Furthermore, a rectangular bay is composed of right-angled triangles in plan.  Pythagoras had something to say about that.

I made a hand-drawn sketch of a triangle within a circle and some parallel planes to assist with parametric adjustments.  It took several attempts to convert this into a sub-component which could be nested 8 times into a vault family.  The parameters are a bit “trial & error” but it works and results in a family that can cover either a square or a rectangle.  That’s as far as I went in the first iteration.

Next little detour was a “PLY” format file that someone downloaded from Sketchfab.  It’s a crowd-sourced photogrammetry reconstruction of Notre Dame.  I managed to open this in an open-source programme called FreeCAD and, after a lot of fumbling around, proceeded to export some images representing orthographic views.  Bringing these into a Revit file with the new grids and levels … it was quite gratifying to see that it fits … more or less.  We know that the axis is bent and the angles are not always square, but our “straightened up” and regularized version of Notre Dame seems to be quite a good representation of the original “design intent”.

Then Francois came up with a book he had acquired.  I think it’s the same one that Ryan showed me at AU and I did mention it in a previous post.  Some drafting over screenshots ensued, to make adjustments to the tower and the spiral stair enclosures.  It’s very easy to get confused in a complex model where everything affects everything else, but I’m confident that we are moving in the right direction.  Actually we have realized since then that the two towers are different widths, reflecting the fact that the aisled of the Nave are wider on the North side.  I’ll come back to that in a future post.

Now for another diversion.  I had talked about the idea of a comparative study of rose window designs, so I decided to take a break for a couple of hours and work on that.  The images are easy to find with any search engine, and for the most part, people have managed to rectify them fairly well.  I could have spent a bit longer correcting the perspective, but they were good enough for me to sketch out the basic geometry of four examples.  It’s too small a sample to say very much but it was a good start.

I had to adjust the size and the alignment of all the arches and vaults down the side aisles.  The nave and the choir are slightly different so that takes time, but the biggest issue is alignment. It’s much easier if you are allowed to twist things slightly out of square.  But we haven’t allowed ourselves that luxury.  I’m confident it would create many more problems than solutions.  The down side is that you have to introduce small offsets here and there, arches that don’t quite line up with the vaults next to them.  It’s a bit like the pixelation you get on lines that are slightly off axis on a computer screen.  For example, the aisles of the choir are slightly narrower than the aisles of the nave.  In reality this means that the transepts are way out of square.  In our model it’s going to mean that the arches on one side don’t line up with the arches on the other.  Maybe we will have to build a vault with one rib that is slightly twisted.

Meanwhile Francois has been busy working on some tracery windows.  My very basic placeholders have been sitting there for some months, so it’s great to see that aspect of the model moving forward.  First examples are around the apse at triforium level.  I still need to adjust the ribs and vaults in this area.  They are the zig-zag type, so it’s pretty fiddly to get them to sit nicely on the clusters of round columns along the wall.

It helps to look at this stuff in Enscape.  Very often I spot problems that are not so obvious when hopping between Revit views.  The night lighting effect is quite accidental I think.  Light seeping in somewhere through a gap or two.  But it’s quite atmospheric all the same with the chandeliers glowing under the arches of the nave.  If you look carefully, you can see that the vaults over the transepts don’t line up with the vertical ribs below.  This is because the Choir is narrower than the Nave.  In real life this is resolved by twisting everything out of square, but I am very reluctant to go that route.


No comments:

Post a Comment

I've been getting a lot of spam so had to tighten up comments permissions. Sorry for any inconvenience. I do like to hear from real people