[HN Gopher] Actually drawing some ovals - that are not ellipses ...
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Actually drawing some ovals - that are not ellipses (2017)
Author : todsacerdoti
Score : 36 points
Date : 2025-03-30 20:44 UTC (2 days ago)
(HTM) web link (medium.com)
(TXT) w3m dump (medium.com)
| notslow wrote:
| Heh, this would have been super helpful last summer as were
| nearing completion on the construction of our new home. We have
| an elliptical arch in our front portico that the carpenter was
| having trouble getting right...
| mauvehaus wrote:
| I'm a little surprised that your architect didn't include
| layout information for the carpenters in their drawings. The
| whole point of the drawings is to enable the builder to
| faithfully reproduce the design, after all.
| nluken wrote:
| I'm not sure if it applies to the original commenter's
| situation but in many places, especially in the US, you don't
| need an architect to build a new home beyond rubber stamping
| some documents on file with the town, and sometimes that's
| not even required.
|
| It's one of the reasons a lot of residential development,
| especially suburban development of the last 40 years, looks
| as bad as it does. Little to no architectural thought goes
| into many new homes beyond what's easiest to build.
| mauvehaus wrote:
| I was kind of hoping that if you have an elliptical (or
| false elliptical) arch that there was an architect involved
| at some point.
|
| I grew up in an area with a lot of corn field subdivisions
| and McMansions. They tend to have a lot of volume/floor
| space and incredibly poor detailing. On the one hand, I
| find it hard to believe that anyone building such a big,
| cheap (at least in the details sense) home on spec would
| include an elliptical arch. On the other hand, the kinds of
| contractors that put them up would likely be the kind that
| struggled to execute such a design element.
|
| I say this having just been very humbled putting up crown
| in a bathroom. People tell me it looks great, and I reply
| that it had sure better considering the two weeks of
| evenings that went into putting it up!
| alabastervlog wrote:
| I've found that absurd, gibberish rooflines, and weird,
| uneven jutting-out bits everywhere, plus garages shoved way
| out in front (?WHY?) _do_ make the houses look bigger,
| which may be desirable for a builder.
|
| I've shopped for houses a lot, and after "training" mostly
| on typical '80s+ suburban houses, noticed that when looking
| at older houses with saner, calmer designs, I'd have to add
| 500-1,000(!)sqft to my first-impression guesses at their
| size to get close, while I'd gotten pretty good at guessing
| the "McMansion" and mini-McMansion style. The older designs
| don't look as big, at the same size.
| dzdt wrote:
| Why is it that a constant curvature is preferable for a builder?
| Is it that construction forms etc are fabricated basically by
| compass and straightedge still?
| dfox wrote:
| If you want the resulting geometry to be precise you are pretty
| much limited to equivalent of compass and straightedge (or
| well, in mechanical engineering lathe and mill, which are
| basically the same things). if you start somehow calculating
| the geometry you are limited by precision of the calculation,
| but more importantly by precision of measuring distances you
| can achieve.
| LegionMammal978 wrote:
| As the author puts it [0], the issue is that if you expand or
| contract an ellipse by a fixed radius in every direction (e.g.,
| if you create inner and outer walls for an elliptical corridor
| of constant width), then the resulting curve is no longer an
| ellipse. In contrast, piecewise-circular arcs can be expanded
| or contracted and remain piecewise-circular, though the control
| points will shift around as you transform it.
|
| [0] https://medium.com/@brunopostle/hey-ovals-are-better-than-
| el...
| dfox wrote:
| Interesting contrast to this is that most modern vector 2D
| graphics API use PostScript/PDF drawing model that cannot
| represent exact circles and elipses and these are instead
| interpolated by a bunch of bezier curve segments.
| fluoridation wrote:
| I don't think that's true. Drawing Bezier curves is not any
| easier than drawing ellipses, and in fact I'm pretty sure it's
| even more difficult. If someone wants to approximate an ellipse
| the easiest solution is to just draw a bunch of short segments.
| brulard wrote:
| Can you provide examples? I have not seen an API not to support
| circles and arcs. SVG is AFAIK the most common API, you have
| there circles, arcs, ellipsis, quadratic and cubic beziers etc.
| memco wrote:
| Did I miss where an actual oval is explained in this method? I
| assume it is just drawing the same arc upside down but wanted to
| be sure there isn't a follow up post or something.
| mauvehaus wrote:
| Yeah, they're symmetrical. You use the three-center method
| doing isometric drawings by hand all the time. The second side
| is a mirror image of the first.
| Isamu wrote:
| The four-centered arch is another one that you see a lot of
|
| https://en.m.wikipedia.org/wiki/Four-centred_arch
| brulard wrote:
| Don't these ovals suffer from the problems of g1 continuity, like
| for example ugly reflections if such an oval is made into a 3D
| reflective object? The reflections getting suddenly tighter where
| arcs connect. Or is it not noticeable if enough arcs are used?
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