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You shouldn't want to actually "get rid" of Mercator entirely. Mercator is pretty great for interactive maps on the Web. Conformal angles, north is always up, s
by rspeer 9y ago
You shouldn't want to actually "get rid" of Mercator entirely. Mercator is pretty great for interactive maps on the Web. Conformal angles, north is always up, splits nicely into tiles.
As long as Africa and Greenland aren't on the same map, it's got almost everything that you want from a map.
Of course, what's best for an interactive map is if it turns into a globe when you zoom out, like Google Earth. instead of being a shitty global Mercator. That's a lot more graphically complex, though.
- mikeash 9y agoRendering a 3D globe onto a 2D screen, centered on the current viewing area and with a fixed orientation, essentially gets what you describe. When you're zoomed in you see something that very closely approximates a Mercator projection cropped to that area. You'll get conformal angles and North is always up. Tiling probably isn't as easy, but it's a Simple Matter of Programming. As you zoom out, it gradually and seamlessly transitions from Mercator-like to globe-like.
- robbrown451 9y agoWhy not have it stay as a globe when you are zoomed in? It will be similar to Mercator, but the aspect ratio would be more accurate especially as you get further from the equator. Admittedly, it is easier for developers who are adding features if you do it as Mercator, but not that much easier (if it has a good API).
- rspeer 9y agoI don't know what you mean about the aspect ratio further from the equator. Mercator is conformal, it preserves angles, so the aspect ratio is 1:1 everywhere that it makes sense to say "aspect ratio". Are you talking about the problem with the shape of a Mercator tile becoming absurd very close to the poles, which I wouldn't call "aspect"? Or are you thinking of the equirectangular projection, where the aspect ratio changes to preserve the distance between latitude lines? The reason not to use a globe is efficiency. Not only is 2D easier than 3D, but you can make Mercator out of tesselated tiles. You can't do that on a globe without having way too many tiles or obvious seams.
- robbrown451 9y agoRight but things like google maps doesn't really use tiles anymore as far as I can tell, they do it using vectors. Tiles suck for lots of things, for instance scrolling can move the street name off the visible map, while doing it as vectors the name can be adjusted.
- rspeer 9y agoThe tiles aren't static raster images, but they're still tiles, made of vector data. You can see them while it's loading. This allows Google to cache the files they serve. And when you pan a Google Map, you're panning a flat Web Mercator projection. If it were a projection of the globe, then everything that's already been rendered would have to be adjusted by imperceptible subpixels to account for the curvature of the Earth.
- robbrown451 9y agoWell if it vector data, the "tiles" can simply be a region of a sphere. That alone is not a reason for Mercator. There may be efficiencies of panning a flat projection, but that is becoming a smaller and smaller issue as devices get more capable. Also, even when in "map mode", you will often notice that google maps is doing more than that. Go to a place where there are tall buildings (I'm looking at downtown san francisco) and you can see the perspective shift on the buildings as it pans.
- rmccue 9y agoSide note: the projection used by Google Maps (and others) is Web Mercator, which is subtly different: https://en.wikipedia.org/wiki/Web_Mercator https://en.wikipedia.org/wiki/Web_Mercator