Implement Web Mercator #67
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scls19fr
reviewed
Feb 14, 2021
src/web_mercator.jl
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| function (trans::WebMercatorfromLLA)(ll::LatLon) | ||
| lat_lim = 85.6 # according to https://epsg.io/3857 |
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I think it's 85.06 or more exactly
const MAX_LAT = rad2deg(2*atan(ℯ^pi)-pi/2)
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Yes this was a typo - thanks!
We could use rad2deg(2*atan(ℯ^pi)-pi/2), that's easy enough. (This is the value which makes the bounding box in northing and easting square, right?)
However I wondered whether the more permissive 85.06 was an intentional choice chosen by the standards body, in order to
- Use a rational rather than irrational number
- Allow some leeway for computing with geometries which have been clipped to the extent of the projection, but are slightly over after numerical error.
andyferris
approved these changes
Mar 20, 2021
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See https://discourse.julialang.org/t/converting-longitude-latitude-to-x-y-on-a-map-using-julia/20611/13
The names
WebMercatorfromLLAandLLAfromWebMercatorseem a bit unfortunate, but the lowercasefromis consistent with the rest of the transformations in this package, and WebMercator doesn't seem to have an obvious shortening. (There's WebMerc maybe, but unclear whether that's helpful.) There's also LatLon support here, but again I usedLLAfor consistency in naming even though it's a bit ugly.