File:Mercator projections vs rotation.gif

Mercator_projections_vs_rotation.gif(800 × 339 pixels, file size: 4.22 MB, MIME type: image/gif, looped, 101 frames, 10 s)

Summary

Description
English: Projecting a sphere on a surface can only be done at the price of some distortion. Mercator's projection is very useful is you are sailing, but strongly distorts sizes. And if we can change what is at the centre of the map we can see how much.
Date
Source https://twitter.com/j_bertolotti/status/1529775116976017414
Author Jacopo Bertolotti
Permission
(Reusing this file)
https://twitter.com/j_bertolotti/status/1030470604418428929

Mathematica 13.0 code

world = CountryData["Countries", "SchematicPolygon"];
swap[c_] := {c[[2]], -(c[[1]] - 90)};
tmp = Flatten[world[[All, 1, 1]], 1];
tmp = Join[tmp, CountryData[\!\(\*
NamespaceBox["LinguisticAssistant",
DynamicModuleBox[{Typeset`query$$ = "antartica", Typeset`boxes$$ = 
         TemplateBox[{"\"Antarctica\"", 
RowBox[{"Entity", "[", 
RowBox[{"\"GeographicRegion\"", ",", "\"Antarctica\""}], "]"}], 
           "\"Entity[\\\"GeographicRegion\\\", \\\"Antarctica\\\"]\"",
            "\"geographic region\""}, "Entity"], 
         Typeset`allassumptions$$ = {{"type" -> "Clash", 
           "word" -> "antartica", 
           "template" -> "Assuming \"antartica\" is a \
continent${separator}Use as ${desc} or ${desc} instead", 
           "count" -> "3", "pulldown" -> "false", 
           "default" -> "{\"C\", \"antartica\"} -> \
{\"GeographicRegion\", \"dflt\"}", 
           "Values" -> {{"name" -> "GeographicRegion", 
              "desc" -> "a continent", 
              "input" -> "{\"C\", \"antartica\"} -> \
{{\"GeographicRegion\", \"a continent\"}}"}, \
{"name" -> "CountryClass", "desc" -> "a class of countries", 
              
              "input" -> "{\"C\", \"antartica\"} -> \
{\"CountryClass\"}"}, {"name" -> "Desert", "desc" -> "a desert", 
              "input" -> "{\"C\", \"antartica\"} -> {\"Desert\"}"}}}},
          Typeset`assumptions$$ = {}, Typeset`open$$ = {1, 2}, 
         Typeset`querystate$$ = {"Online" -> True, "Allowed" -> True, 
          "mparse.jsp" -> 0.773653`6.340091207439451, 
          "Messages" -> {}}}, 
DynamicBox[ToBoxes[
AlphaIntegration`LinguisticAssistantBoxes["", 4, Automatic, 
Dynamic[Typeset`query$$], 
Dynamic[Typeset`boxes$$], 
Dynamic[Typeset`allassumptions$$], 
Dynamic[Typeset`assumptions$$], 
Dynamic[Typeset`open$$], 
Dynamic[Typeset`querystate$$]], StandardForm],
ImageSizeCache->{225.2265625, {8.11328125, 17.11328125}},
TrackedSymbols:>{Typeset`query$$, Typeset`boxes$$, 
            Typeset`allassumptions$$, Typeset`assumptions$$, 
            Typeset`open$$, Typeset`querystate$$}],
DynamicModuleValues:>{},
UndoTrackedVariables:>{Typeset`open$$}],
BaseStyle->{"Deploy"},
DeleteWithContents->True,
Editable->False,
SelectWithContents->True]\), "SchematicPolygon"][[1, 
    1]]];
world2 = Reap[For[j = 1, j <= Dimensions[tmp][[1]], j++,
      Sow[\[Pi]/180 (swap /@ tmp[[j]])];
      ];][[2, 1]];

ToSphere[c_] := {Cos[c[[1]]] Sin[c[[2]]], Sin[c[[1]]] Sin[c[[2]]], Cos[c[[2]]]};
sphereworld = Reap[For[j = 1, j <= Dimensions[world2][[1]], j++,
      Sow[(ToSphere[#] & /@ world2[[j]])];
      ];][[2, 1]];
ToMercator[c_] := {c[[2]], -Log[Cos[-(c[[1]] - \[Pi]/2)/2] - Sin[-(c[[1]] - \[Pi]/2)/2]] + Log[Cos[-(c[[1]] - \[Pi]/2)/2] + Sin[-(c[[1]] - \[Pi]/2)/2]]};
sinstep[t_] := Sin[\[Pi]/2 t]^2
frames = Table[
   m = RotationTransform[-2 \[Pi] sinstep[t], {0, 1., 0}];
   rotatedsphereworld = 
    Reap[For[j = 1, j <= Dimensions[sphereworld][[1]], j++,
        Sow[(m /@ sphereworld[[j]])];
        ];][[2, 1]];
   mercatorworld = 
    Reap[For[j = 1, j <= Dimensions[rotatedsphereworld][[1]], j++,
        Sow[(ToMercator[#] & /@ (CoordinateTransform["Cartesian" -> "Spherical", rotatedsphereworld[[j]]][[All, 2 ;; 3]]) )];
        ];][[2, 1]];
   mercatorworld2 = 
    Reap[For[j = 1, j <= Dimensions[mercatorworld][[1]], j++,
        Sow[Split[mercatorworld[[j]], Abs[#2[[1]] - #1[[1]]] < 1 &]
          ];
        ];][[2, 1]]; 
   GraphicsRow[{
     Graphics3D[{Thick, Line /@ rotatedsphereworld, LightGray, Sphere[{0, 0, 0}, 1]}, Lighting -> "Neutral", Boxed -> False, ViewPoint -> {2, 0, 0}]
     ,
     Graphics[{Line /@ mercatorworld2, Thick, Line[1.01 {{-\[Pi], -\[Pi]}, {-\[Pi], \[Pi]}, {\[Pi], \[Pi]}, {\[Pi], -\[Pi]}, {-\[Pi], -\[Pi]}}]}, PlotRange -> 1.*{{-\[Pi], \[Pi]}, {-\[Pi], \[Pi]}},       AspectRatio -> 1/1.61803, ImageSize -> 500]
     }]
   , {t, 0, 1, 0.01}];
ListAnimate[frames]

Licensing

I, the copyright holder of this work, hereby publish it under the following license:
Creative Commons CC-Zero This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication.
The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.

Captions

Earth projected using Mercator as a function of north-south rotation.

Items portrayed in this file

depicts

26 May 2022

image/gif

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Date/TimeThumbnailDimensionsUserComment
current09:26, 27 May 2022Thumbnail for version as of 09:26, 27 May 2022800 × 339 (4.22 MB)BertoUploaded own work with UploadWizard

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