That's just a circular argument
A not-quite-circular argument, even!
Circles do not exist
131–140 of 217 posts
Re: Circles do not exist
#132Earlier quoted context omitted.
if being off by 3 units on a 10,000 unit circle actually matters, you have stricter requirements than most industry bodies. If you're fabricating parts that have tolerances measured in 1/10th of a thou , the machines you use absolutely don't ask for PDF, they ingest proper control code.
Control code generated from a CAD model, not a .pdf. Al you need to fix this is use rational Beziers - same thing but with weighted control points. STEP files will remain the standard for CAD.
> Al you need to fix this is use rational Beziers - same thing but with weighted control points.
Then it is settled, we'll use .TTF as our CAD interchange format.
Re: Circles do not exist
#133That's pretty interesting. I'll now be doubting every circle I walk by, questioning if it's even real or just some approximation.
Perfect shapes do not exist on a physical level, so they're all approximations https://factmyth.com/factoids/there-are-no-straight-lines-or...
Which is why I could never truly appreciate calculus.
Re: Circles do not exist
#134If you use the standard way to approximate a circle with Bezier curves, it will differ from a true circle by about 0.03%. The human eye is not capable of seeing the difference, and, as the OP mentioned, most people can't accurately eyeball a perfect circle anyway. This post shows the math behind that, and then shows that it could be made even better with a few different choices. https://spencermortensen.com/articles/…
I think the OP is really just frustrated with the idea that CAD will use PDF and, in that application, 0.03% deviation can be too much.
Seems like the real actual data would just be embedded inside the pdf.
Hopefully anyway.
Re: Circles do not exist
#135I thought the article would go further and posit that Circles do not exist in reality as they are approximations of a mathematical ideal. But the author does present the raster image as a bonafide circle, rather than the approximation that it truly is -- more resolved than others or not. A zoomed in excerpt of the author's rasterized circle approximation clearly shows that scale is key in perception of reified ideals…
That's true in a sense, but you've got to go way down. At a fine enough level --- say, at the level of atoms --- all material things are granular, and circular or spherical things are built stepwise from material building blocks, as though from pixels. Thus even very "smooth" things are rough and granular. Further: There are no circular (2D) molecules; nature prefers hexagons and other polygons for that. Even the pro…
Is similar not also true of Lines, and Points?
That is: every real, non-theoretical Point must have a size, a resolution; and every non-theoretical straight Line is surely not a true straight line if we zoom far enough down into sub-atomics.
Re: Circles do not exist
#136Please note that most pistons and cylinder bores are also not circles ;-)
...and haven't been for at least 76 years: https://news.ycombinator.com/item?id=15397926
(Original page seems to have moved; it is now here: https://www.web.imperialclub.info/Repair/Lit/Master/003/inde... )
Re: Circles do not exist
#137Earlier quoted context omitted.
Yes, that's the point. 1. PDF is to become a standard CAD interchange format. 2. Using PDF where 0.03% matters is insane. 3. If CAD requires 0.03% tolerance, then using PDF as a standard CAD interchange format is insane. I would imagine you generally want arbitrary precision for CAD.
Absolutely! I cannot imagine a CAD system that can't symbolically represent what is actually desired. The model and its spec should be one and the same. Approximations also open the door to different precision versions. Not helpful when different parts from different sources need to be consistent. Models that approximate/vary from the ideal spec, created intentionally to match manufacturing limitations, are ok.
Drawings for parts should have tolerances called out. I did mechanical inspection for a manufacturer for several summers. Every dimension had a plus/minus value listed. Holes and screw threads had go/no-go gauges
Re: Circles do not exist
#138Earlier quoted context omitted.
if being off by 3 units on a 10,000 unit circle actually matters, you have stricter requirements than most industry bodies. If you're fabricating parts that have tolerances measured in 1/10th of a thou , the machines you use absolutely don't ask for PDF, they ingest proper control code.
Control code generated from a CAD model, not a .pdf. Al you need to fix this is use rational Beziers - same thing but with weighted control points. STEP files will remain the standard for CAD.
Does STEP not have circles? Because g-code has G2 which seems like it should draw an actual circle (G2 X0 Y0 R100 or similar).
Re: Circles do not exist
#139Earlier quoted context omitted.
Or just use the ellipse (E) in Inkscape, set the start/end to 0, and hold down ctrl. Then inkscape will generate a ` ` svg element.
But the SVG in Inkscape is not a PDF on a machine that accepts PDF CAD drawings. When you print to PDF, the circle will have to be approximated, which is what the article is talking about.
The article was about postscript, but the comment I was replying to was about how to approximate a circle in Inkscape, so I suggested a better approach.
Re: Circles do not exist
#140>>one of the cases PDF is being considered (and, based on Internet rumors, is already being used) is as an interchange format for CAD drawings? Now it suddenly starts mattering. If you have any component where getting a really accurate circle shape is vital (like pistons and their holes), suddenly all your components are slightly misshaped. Which would not be fun.
Holy forking shirtballs - NO!
The article rightly make a nice concise case against it.
I'd add from my experience: perhaps PDF people think this would be a cool way to make more money, but only because they have not done any CAD/CAM/CNC work. Since I do CAD/CAM/CNC as a regular part of my work, and have spent time with PDF back to it's early days, that is a hard NOPE.
But definitely a good nominee for the Bad Ideas Hall Of Fame, at least honorable mention.
sheesh.