<div dir="ltr"><div dir="ltr">Thank you all for your very detailed explanations!</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 26 Nov 2020 at 16:53, Lesparre, Jochem <<a href="mailto:Jochem.Lesparre@kadaster.nl">Jochem.Lesparre@kadaster.nl</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><span lang="EN-GB">Hi Idan,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">I would like to point out a few issues:<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<li class="gmail-m_-3716671210987045589MsoListParagraph" style="margin-left:0cm"><span lang="EN-GB">WGS84 is not a projection, therefore it has no projection distortions. The world is an ellipsoid in WGS84, not a rectangular map.
The deformations you refer to is what you get when ones uses the platte-carée projection (x=longitude, y=latitude) as for instance QGIS does by default. Google Earth instead uses a globe for WGS84, so it has (almost) no distortions.<u></u><u></u></span></li><li class="gmail-m_-3716671210987045589MsoListParagraph" style="margin-left:0cm"><span lang="EN-GB">EPSG:4326 is a bad choice for a CRS, as it is 2D and because it is a datum ensemble. It is better specify a specific reference
frame (e.g. WGS84-G1761). Or even better: to use the official international terrestrial reference system (e.g. ITRF2014) in stead of a CRS defined by the military of one random country.<u></u><u></u></span></li><li class="gmail-m_-3716671210987045589MsoListParagraph" style="margin-left:0cm"><span lang="EN-GB">Web Mercator is an approximation mixing spherical formulas and ellipsoidal coordinates. Therefore it is not conformal. True Mercator
is a better choice as it is conformal. I do not believe the more complex computation is a real problem for modern computers.<u></u><u></u></span></li></ul>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Kind regards, Jochem<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> PROJ <<a href="mailto:proj-bounces@lists.osgeo.org" target="_blank">proj-bounces@lists.osgeo.org</a>>
<b>On Behalf Of </b>Idan Miara<br>
<b>Sent:</b> donderdag 26 november 2020 14:47<br>
<b>To:</b> PROJ <<a href="mailto:proj@lists.osgeo.org" target="_blank">proj@lists.osgeo.org</a>><br>
<b>Subject:</b> [PROJ] Why is Web Marcator EPSG:3857 so popular for web maps (vs EPSG:4326)?<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">Hi all,<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">I was wondering if you can enlighten me regarding why Web Marcator (</span><span lang="EN-GB" style="font-size:10.5pt;font-family:Arial,sans-serif;color:rgb(32,33,34)">EPSG:3857) is so popular and used by virtually all major
online map providers as opposed to WGS84 lat/lon (EPSG:4326)?</span><span lang="EN-GB"><u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">I've composed some points that I could think about, but it doesn't add up for why 3857 maps (i.e. slippy map) are more popular than 4326:<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">1. In 3857 almost all the world fits in a rectangular tile (~85 deg north to ~</span><span lang="EN-GB" style="font-size:10.5pt;font-family:Arial,sans-serif;color:rgb(32,33,34)">85 deg south), which makes it easier to divide the
tile further into sub tiles. </span><span lang="EN-GB"><u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:10.5pt;font-family:Arial,sans-serif;color:rgb(32,33,34)">In 4326 all the world fits into two rectangular tiles (so not much more complicated, I guess).</span><span lang="EN-GB"><u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:10.5pt;font-family:Arial,sans-serif;color:rgb(32,33,34)">2. Users expect coordinates in 4326 and the transformation from 3857 to 4326 is rather fast (in comparison to ellipsoidal mercator).</span><span lang="EN-GB"><u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">But if you save the coordinates in 4326 then you wouldn't need to transform at all.<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">3. 3857 is "almost" conformal - I think that the normal use case is not marine navigation so it doesn't seem so important.<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">4. Both 3857 and 4326 have size distortion.<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">5. You can't measure distances, areas or angles easier in 3857 as far as I know.<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB">What am I missing? Is 3857 faster or more useful in any other way than 4326?<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
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<p class="MsoNormal">Kind regards,<u></u><u></u></p>
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<p class="MsoNormal">Idan<u></u><u></u></p>
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