File talk:Guyou doubly periodic projection SW.JPG

Botched rendering
This map image, as it is today, is a horror. It cuts off western Europe at the top splits and distorts western Europe beyond recognition.

Compare this map image with all other renderings of Guyou's Doubly-Periodic Projection (web search). Whether with continent outlines or colored continents and oceans, they do not share this problem. Examples:
 * A distortion map of Guyou's - outlines, 10° grid, indicatrix. (here on Wikipedia) (This map image and the distortion map are both displayed on Guyou hemisphere-in-a-square projection.)
 * Guyou: Compare Map Projections - color map, 15° grid. Also a more-complete indicatrix. "In the image, the projection is centered on 20° West in order to keep the landmasses away from the areas of greatest distortion (where conformality fails)."
 * Guyou's Doubly-Periodic Projection - outlines, 30° grid. Explores similar grids.
 * Conformal Projections Intro - outlines and explanations. See "Classic Guyou map, central meridian 20°E, poles at midpoints of hemispheric edges" (enlarged here). It also shows a vertical offset here, "Oblique Guyou map with poles at square vertices, or two Adams hemispheres; central meridian 25°W".
 * Guyou Conformal - outlines, 10° grid.

(Some of these are public domain or CC.)

Guyou's Doubly-Periodic Projection uses heavy distortion. It actually does not make a complete world map. It distorts some regions beyond recognition due to singularities, the bane of conformal projections. Across the vertical centerline is a span where everything north of 50°N or south of 50°S is projected right out of the rectangle shrunk, twisted, and even inverted. Guyou's Doubly-Periodic Projection puts much ocean area across the centerline, but no one notices that four "featureless" ocean areas are missing distorted beyond recognition.

This map image uses the same distortion as the original. (That is not immediately obvious, because this map has 15° line spacing and the distortion map has 10° line spacing.) This map image puts the equator (0°N) on the horizontal centerline, also the same.

The difference is: This map image is centered on the Prime Meridian (0°E), which puts western Europe across the centerline, making it disappear, distorting it beyond recognition, which is a deal breaker. The original map is always centered on 20°W longitude.

This map image nicely keeps New Zealand with Australia and doesn't break up Siberia as badly, but scrambling western Europe is not worth it. (In the actual Guyou's Doubly-Periodic Projection, people in Australia, Pacific islands, and Pacific Rim could swap the left and right halves, yielding a map centered at 160°E, which is also a very nice view.) -A876 (talk) 19:50, 14 February 2022 (UTC)


 * The image isn’t botched, and you are wrong in what you report about the projection. The projection does make a complete world map, and Europe is not “projected right out of the rectangle” in the one you are complaining about. It’s all there; you just have to understand what you see. The purpose of that image is not to give you a satisfying world reference map. The purpose is to provide an image of the projection in a standardized format: that is, using the prime meridian as a central meridian. Strebe (talk) 01:09, 17 February 2022 (UTC)


 * I expected better work. I expected a better response. You botched it, no two ways. Thanks. -A876 (talk) 01:16, 17 February 2022 (UTC)


 * You expect better work from someone you paid nothing to, who owes you nothing, and yet who gave the world this featured image. You expect a better response when your initial posting displayed contempt and ignorance. I think everyone knows who botched what here. Strebe (talk) 01:52, 17 February 2022 (UTC)


 * I expected, from a Expert, a rendering that does not nullify the merits of the projection, but hey, silly me.
 * I expected something like "oops", or "good catch", but no. Instead of addressing the claim, you: Remind me that You are a Volunteer. Tell me how great You ARE. Criticize my "style". Tell me I'm contemptuous. Tell me I'm stupid. Lawyer everything away, like some untouchable academic. It's all there. All classic. Kill the messenger. Rationalize. Project. (My sad luck who I encounter.) Such professionalism. Such skill and expertise. This is a feather in your cap. Aside from that,
 * I stand corrected (edits above) on this: I guess that must be northern England there, tiny, upside-down, and separate from the rest of England. Without more gridlines, it's hard to intuit that the entire globe really is mapped, though with near-infinite distortion in places. This grid twists so much, a distortion map would be more complete if it added a north-pointing arrow inside each box.
 * "The purpose of that image is not to give [the world] a satisfying world reference map." Mission accomplished. But the purpose of most every map projection is to give [the world] a "satisfying" (haha, funny) world "reference" map.
 * "The purpose is to provide an image of the projection in a standardized format: that is, using the prime meridian as a central meridian." Really? That sounds like a wrong purpose. Changing the specification of the projection? In a way that makes a nice projection look like crap? That sounds like a really wrong purpose. An abuse really. (I'd contact Guyou, but he's dead.)
 * It is tragic that this image was ever featured, because it does not show Guyou's Doubly-Periodic Projection; it shows something quite else. It really deserves re-rendering to not be so embarrassing. -A876 (talk) 19:46, 17 February 2022 (UTC)


 * Are you not acknowledging your attack of Strebe's map, based on your false assumptions? You have now admitted you were wrong, but you do not follow it with an "oops" or an apology, yet you expect something similar from the person you attacked unfairly even though they did nothing wrong. That's hypocritical, is it not?
 * Strebe addressed your claims. (What claim do you think hasn't been addressed?) You didn't have a "good catch" so it's nonsensical that you would be praised for one. Strebe had nothing to say "oops" about; only you did.
 * Are you here to tell people that their work "look[s] like crap"? And call them an "untouchable academic"? Strebe didn't call you contemptuous or stupid; he pointed out that your first post contained both, which is indisputable. (Do you have another explanation for calling his map a "horror"? Was your false claim not, in fact, due to ignorance?) I'm not sure why you're being so incredibly uncivil, but it has no place here. NoesisDianoia (talk) 23:04, 17 February 2022 (UTC)
 * Amazing, you're here in two places now. You think I "attacked" "Strebe's map"? I stood corrected; I saw it wrong – Europe isn't off the map, it's merely twisted beyond recognition. (Good idea, though. "Strebe's projection" would be a great name for it, because it certainly is not Guyou's projection.) So you're our referee? You say I didn't "win"? You echo his badguy claim? You think I attacked him? I said "I expected" (the past tense), after being disappointed. I don't "expect" anything. Having been disappointed I can't expect anything. I didn't say "I expect" anything - saying "I expect" is a request, demand, or order, which I do not make. The rendering really is ugly. Did I fail to sugar-coat it? Yes. Did I fail to suck up? Yes. Sorry, Mom. -A876 (talk) 06:06, 18 February 2022 (UTC)


 * What more were you hoping for in a response? Strebe's response seems fine to me. All of Europe is there, like Strebe said; nothing is missing. It's understandable how you are having trouble interpreting the projection because of how it folds, but the projection isn't botched in any way. Why are you continuing to insist that it is? Which part of Europe, precisely, are you claiming is missing? NoesisDianoia (talk) 19:04, 17 February 2022 (UTC)
 * And another jumps on the pile-up. -A876 (talk) 19:46, 17 February 2022 (UTC)
 * My one comment and question is a "pile-up"? How so? NoesisDianoia (talk) 23:04, 17 February 2022 (UTC)
 * No one needed you to conveniently take a side or play "pound the Philistine". Your account made one edit in 2014, edited its user page again in 2018, and then, suddenly, in 2022, this topic became dear? Your account either never browsed or never edited. If you edited a lot, you either used a different account(s) or never logged in. It looks like a "sleeper" account woke up to echo and praise every disputed defense, like a sycophant or star lawyer. It's as if you sit next to him somewhere. "All of Europe is there" – indeed, wrapped around a singularity of infinite distortion. -A876 (talk) 06:06, 18 February 2022 (UTC)


 * Let’s see how this might have gone in a world of healthy communication:
 * Alt A876: “I see this rendition of Guyou is very unfavorable to Europe — in fact, it looks like a lot of Europe has been shoved out of the projection entirely. And yet this image is the reference image on the Guyou hemisphere-in-a-square projection page.”
 * Strebe: “Interestingly, the projection does actually display the entire world, but I can see how that’s not obvious. It’s just extremely distorted. It splits apart northern Europe through the prime meridian. I did it that way to keep the prime meridian as the central meridian for comparative purposes in the large suite of standardized map projection images I created for Wikipedia articles.”
 * Alt A876: “Ah, okay. But if someone were to want to use the image as a base map for a real map, it wouldn’t be very useful that way. It’s also not useful for showing how the projection could be used for a serious map.”
 * Strebe: “Those are good points.”
 * Alt A876: “Would it be too much trouble to create an image with the 20°W meridian as the central meridian? Most [Editorial note: the “all” claim above is false; do your own search] of the images I have seen use 20°W, and I think Guyou recommended that.”
 * Strebe: “It would make sense to make one available. I’ll see if I can get to it.”
 * Alt A876: “Thanks. I’d also like to use it for the article page, too, though. What do you think about that?”
 * Strebe: “I might be persuaded. Or even, for educational purposes, we could show both images. That could help the reader understand how the distortion changes across the map. In any case, we can open it up for discussion on the article talk page if I get a new image prepared.”
 * Alt A876: “Cool. Cheers. Looking forward to it if you can.”
 * Strebe (talk) 03:59, 18 February 2022 (UTC)

See, that wasn't so hard. (kidding) Yeah I guess it was harder than it had to be. Going forward, I'll try to be more considerate, though it takes additional rewrite before posting to recast my objections with less-brutal honesty. I didn't encounter any Guyou or variant that didn't choose a meridian offset to avoid putting land-area in a singularity, except maybe as counterexamples. (I know I'm limited to what's online. One nice set I only found by accident; an image on Pinterest and Tumblr linked to a vanished website now available only via Internet Archive.) The primality of the Prime Meridian isn't absolute; there have been several over the centuries, though 0° longitude is a familiar line. Some projections cannot tolerate adding a meridian offset; for example, the Goode homolosine projection would become gruesome, with rifts splitting continents instead of oceans. I think the Guyou has to be treated the same way. -A876 (talk) 06:06, 18 February 2022 (UTC)