Thanks, I used the authoritative sources and made the math myself. I believe the OSM website at [2] should be fixed accordingly. The radius used in the sources [1, and elsewhere] is in fact as expected the WGS_84 sphere of radius 6378137.0. It means the radius (which is said to be 6372.7982 km, that’s about 40 km missing at the equator) and tile sizes at [2] should be fixed for others who want to do funny things and get mislead by these values.
I also believe the degree column should be removed from the table. Because the tiling scheme is a tile pyramid, where the tile sizes are cut in half for each subsequent level. That isn't the same as cutting the degree into half as shown in the table. For example, the length at zoom level 19 for 0.0005° at the equator is 0.21742088 using haversine - and not 0.29858214 which is the value you get cutting the extent into halfs. So the page should be updated to (note the different sphere and m/ pixel values): sphere: 6378137.0 The math for m / pixel is: z0: (6378137 * 2 * pi) / 256 z1: (6378137 * 2 * pi) / 256 / 2 … Level Degree Area m / pixel ~Scale 0 360 whole world 156543.033928 1:500 million 1 180 78271.516964 1:250 million 2 90 39135.758482 1:150 million 3 45 19567.879241 1:70 million 4 22.5 9783.9396205 1:35 million 5 11.25 4891.96981025 1:15 million 6 5.625 2445.98490513 1:10 million 7 2.813 1222.99245256 1:4 million 8 1.406 611.49622628 1:2 million 9 0.703 wide area 305.74811314 1:1 million 10 0.352 152.87405657 1:500,000 11 0.176 area 76.43702828 1:250,000 12 0.088 38.21851414 1:150,000 13 0.044 village or town 19.10925707 1:70,000 14 0.022 9.55462853 1:35,000 15 0.011 4.77731426 1:15,000 16 0.005 small road 2.38865713 1:8,000 17 0.003 1.19432856 1:4,000 18 0.001 0.59716428 1:2,000 19 0.0005 0.29858214 1:1,000 Ben [1] https://github.com/openstreetmap/mod_tile/blob/6b9611aaf763f4f776d1fd363433aac7e25cb34b/src/gen_tile.cpp [2] http://wiki.openstreetmap.org/wiki/Zoom_levels Von: Komяpa <m...@komzpa.net<mailto:m...@komzpa.net>> Datum: Samstag, 18. Juni 2016 um 07:38 An: Benjamin Stadin <benjamin.sta...@heidelberg-mobil.com<mailto:benjamin.sta...@heidelberg-mobil.com>>, OSM Dev List <dev@openstreetmap.org<mailto:dev@openstreetmap.org>> Betreff: Re: [OSM-dev] Earth radius Hi, OSM uses EPSG:4326 for storing coordinates and EPSG:3857 for rendering. You can get projection definitions on http://epsg.io/4326 and http://epsg.io/3857 respectively, or find it bundled with proj4 library that is widely used to deal with projection nuances. сб, 18 июн. 2016 г. в 1:37, Stadin, Benjamin <benjamin.sta...@heidelberg-mobil.com<mailto:benjamin.sta...@heidelberg-mobil.com>>: Hi, I want to double check the earth radius used by OSM and zoom levels is exactly 6372.7982 as said here: http://wiki.openstreetmap.org/wiki/Zoom_levels. I couldn¹t find this as constant in the sources yet. I¹m creating a new storage system for vector tiles, independent of a projection. Best Ben _______________________________________________ dev mailing list dev@openstreetmap.org<mailto:dev@openstreetmap.org> https://lists.openstreetmap.org/listinfo/dev
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