Tue, 27 Feb 2024

Cardboard Haberdashery

— SjG @ 5:42 pm

The annual Venice Mardi Gras parade was on the 25th (due to scheduling issues, that’s the midst of Lent this year!), so it was time to make a costume.

As the self-appointed official unofficial photographer, I always need to be able to wield one or more cameras, so my costumes tend to focus on some kind of headgear that won’t get in the way. Past costumes have included wild structures to hide a fill-in flash, wizard hats, a big papier-mâché fish, and the like. This year, since the theme is “Magical Mystery Trip,” I figured a variant on a top-hat would hint at magicianishness. A magical geometrical figure adds to the alchemical implications, so I put a Mardi Gras themed dodecahedron on it.

The top hat itself is made of cardboard. I started by measuring my head with a piece of string, cutting out a sheet from a delivery box (the corrugations pulled over the hard edge of the table to make it flexible), and creating a cylinder. Duct tape was used inside to hold it together. A top plug was hand-drawn, cut out, and hot-glued into place. Oh, so much hot glue. It’s great for imprecise work like this: it fills gaps, is adjustable for those vital few seconds, but hardens quickly into a pretty good secure bond. The brim was then drawn onto a sheet of chipboard, cut, positioned, and glued. After that, I cut the cylinder down to the curve with a razor blade, and taped in some padding with gaffer tape to help smooth that edge.

Then the hat part got put aside for a bit while the decoration was implemented. A dodecahedron is a geometric solid made of twelve pentagons. To add interest, I used Affinity Designer to illustrate a collection of pentagonal patterns based on fleurs-de-lis. You can download the design file as a PDF.

I took the file and a pack of acid-free chipboard to CrashSpace, and zapped out a bunch of pentagons on the trusty Epilog laser cutter. The chipboard comes in sheets that are 12 by 12 inches and “medium weight” which translates to 0.057 inches (~1.47mm) thick. Because the boards are not perfectly flat, the laser cutter doesn’t cut exactly the same across the entire sheet, meaning that some of the cut-out areas aren’t completely cut out.

In the vinyl- and paper-cutting crafts world, they refer to removing the cut-out portions from a design with the delightful term “weeding.” For most of the patterns, weeding just involves popping out the loosely connected portions. But there are places where I got poor through-cut. Also, the density of the chipboard is not very uniform, so some areas took a lot of cleanup with an X-Acto knife.

If I had been wiser, I would have recut these at a slightly slower speed to make sure there was complete cut-through.

Then, out came the hot-glue again, and the pentagons were assembled into a dodecahedron. You can kind of see in the lower left corner of picture below a temporary jig I made for positioning the pentagons into groups of three for rapid gluing. It’s not very precise, but fortunately it doesn’t need to be.

Next came painting. I have a set of metallic acrylic paints that were bought for last year’s Mardi Gras mask. In retrospect, I should not have bought them as the “metallic” effect is produced by tiny plastic flakes like glitter. Ugh. Micro-plastics. We’re all full of ’em, and it’s only getting worse. But I already have the paints, so I decided to use them.

The final result didn’t end up looking half bad. I wore a not-terribly-clashing floral front-plate for my FloMask to complete the look.

In the spirit of Mardi Gras, at the end of the parade, the hat was given to a school teacher whose students had just learned about dodecahedrons.

Tue, 23 Jan 2024

The Moon and a Lens

— SjG @ 6:59 pm

From my desk, I could see the the waxing gibbous moon rising. The geometry was such that the moon filled the gap between the open venetian blinds almost exactly. I took a picture with a 300mm lens, focused on the moon.

The moon behind venetian blinds

I was a little surprised how much the venetian blinds in the foreground blurred out over the moon when I did that. When looking through the viewfinder, the image seemed to match what my eye saw: the moon filling the gap between two horizontal lines.

Thinking about it, it made sense. I had the aperture at f/8, so the limits to the depth of field would cause the much closer objects to blur.

I took a few steps closer to the window, so there would be more of a gap between the blinds, and took another picture.


Although to my eye, the moon was only about 75% of the gap between the venetian blinds, the depth-of-field problem continued to obscure it. So I went even closer.


Even though the moon was taking up half the gap (to my eye), the venetian blinds still obscure it. So I went right up to the window, where the view through the lens made it seem like there was no obstruction whatsoever, just a moon floating there.


Well, even at this point, the venetian blinds intruded upon the image. Thinking about it more, I realize that the diameter of the lens is bigger than the gap between the venetian blinds. The lens gathers light from all across its diameter, so there’s no way it can see “between” the slats — the light is blocked. Also, as I got closer to the blinds, I was asking the lens for more depth of field (which it could not give me). The slats went further out of the focus and are relatively more blurred. In all likelihood, I didn’t see the effect through the viewfinder because I wasn’t paying sufficient attention.

Back in the day, I probably could have found the right equations to explain this phenomenon. Today, I’m content to notice it and say “Hm. Interesting.”

Sat, 13 Jan 2024

House Mountain Model

— SjG @ 5:45 pm

I’m not sure how, but at some point I came across this Instructables article on building models from maps. The article shows you how to use Terrain2STL and Kiri:Moto to get a portion of a map, generate a elevations file in STL format (originally designed for stereolithography, it’s a format supported by lots of 3D programs and tools), and convert that file into topographical slices.

So I revisited the House Mountain area, and went through the process. I chose to exaggerate the vertical considerably to make it more identifiable. The tools yielded me an SVG graphic of all the layers. I did further conversion, and cut the scene out of chipboard using CrashSpace’s Epilog laser.

I lost many of the finer peak tops into the interstices of the laser cutter. Even the ones I did manage to keep were difficult to glue. I’d use a magnifier and tweezers if I were to do it again.

I’m tempted to 3D print the STL file on a filament printer. The output would certainly be smoother and more detailed.

Sun, 7 Jan 2024

Parametric Architecture

— SjG @ 4:13 pm

In ye olde days, I designed stuff in POV-Ray to render whatever fantastical scenes I was imagining. I’d spend hours figuring out textures and constructive solid geometry to create images. It was a slow process. Files were extremely slow to render. On my trusty Intel 80386-based PC running DOS, a scene of any complexity would take all night to render at 640×480 pixels.

Now, 30-some-odd years later, I still play with a constructive solid geometry modeler — in this case, OpenSCAD. The idea is that I could output the models to a format like STL, and then 3D print them into physical being. I haven’t actually done very much printing of models, but it’s an interesting possibility nonetheless.

By Pieter Brueghel the Elder – Levels adjusted from File:Pieter_Bruegel_the_Elder_-The_Tower_of_Babel(Vienna)_-_Google_Art_Project.jpg, originally from Google Art Project., Public Domain,

Below are some images from a work in progress. I was inspired by seeing the Breugels painting above in a YouTube video. The tower is not only a great metaphor, but an interesting image and architecture.

My architectural thoughts go more Gothic (more flying buttresses), and parametric. By parametric, I mean that I figure the design can be based on a set of variables, for example, the ratio of height to width of a wall segment. For each value of the variables, the code can generate the appropriate geometry.

My ability to create this way is limited by two things: my trigonometry is not particularly strong, and my ability to keep a stable 3D point of reference in my head is even worse. So I start with sketches and pages of cosines and arctangents, and then end up doing a lot by trial-and-error. Because thinking in this mathematical space is hard, I end up getting frustrated and putting the project aside for days or months before picking it up again. Not to mention, even with today’s super-fast computers, as the complexity increases, the time to render an image increases!

So, my tower of Babel is not complete. There’s been some progress. I played with it a little today. Maybe one day I’ll finish it. Perhaps I’ll even print a model.

Thu, 28 Dec 2023

Welcome to the Fediverse

— SjG @ 5:03 pm

I’ve hooked up this blog to the fediverse. The improved visibility will doubtless increase readership from none to the lofty realms of zero.

Posts will federate as posts/toots/notes from @admin. Presumably, comments/responses will propagate back somehow too. I could read the manual, but I’m just going to sit back and see what happens.