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--></style></div><div>a full Technical description of code 3857 epsg (and his trouble about measurement) here :<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>https://alastaira.wordpress.com/2011/01/23/the-google-maps-bing-maps-spherical-mercator-projection/<br></div><div><br data-mce-bogus="1"></div><div>so long...<br data-mce-bogus="1"></div><div><br></div><div data-marker="__SIG_PRE__"><hr>
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<td style="font-family: arial; font-size: 10pt"><b>Julien-Pierre GUILLOUX</b><br>
Chargé de mission Eau, Forêt, Natura 2000, coordinateur des porter-à-connaissance<br><br>
<span style="color: #999999;">
<b>Parc national des Écrins</b><br>
04 92 40 20 56 / 06 99 77 38 26<br>
<a href="http://www.ecrins-parcnational.fr/" style="COLOR:#999999;FONT-WEIGHT:normal;TEXT-DECORATION:none" target="_blank">www.ecrins-parcnational.fr</a>
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</tbody></table><div><br></div></div><div><br></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><b>De: </b>"Julien Guilloux" <julien.guilloux@ecrins-parcnational.fr><br><b>À: </b>"Michel Stuyts" <michel.stuyts@edegem.be>, "Springfield Harrison" <stellargps@gmail.com>, "qgis-user" <qgis-user@lists.osgeo.org><br><b>Envoyé: </b>Vendredi 18 Mai 2018 11:01:04<br><b>Objet: </b>Re: [Qgis-user] results Measure Tool vs. length()<br></div><div><br></div><div data-marker="__QUOTED_TEXT__"><div style=""><div style="font-family: arial,helvetica,sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"><div style=""></div><div style="">Hi Michel,<br style=""></div><div style=""><br style=""></div><div style="">Never use epsg 3857 for measurement beacuse it is not a "projection"... </div><div style="">this "pseudo projection mercator" 3857, called often "Popular Visualisation" is pseudo.... Because only use for visualization applications. <br style=""></div><div style=""><br style=""></div><div style="">example in France : 3200 km for a road for example, instead of 2100 km in a real projection (as local zone UTM or a Lambert projection)<br style=""></div><div style=""><br style=""></div><div style=""><br style=""></div><div style="">So, you can use qgis, esri, postgis etc... the measurment with 3857 will be always bad, due to a "false" calcul from origine 0,0 (equateur cross greenwich) and "false" ellipoide etc....<br style=""></div><div style=""><br style=""></div><div style="">best regards,<br style=""></div><div style="">Julien<br style=""></div><div style=""><br style=""></div><div style="">have a look on :<br style=""></div><div style="">http://spatialreference.org/ref/sr-org/6864/<br style=""></div><div style=""><br style=""></div><div style=""><hr style="">
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<td style="font-family: arial; font-size: 10pt;"><b style="">Julien-Pierre GUILLOUX</b><br style="">
Chargé de mission Eau, Forêt, Natura 2000, coordinateur des porter-à-connaissance<br style=""><br style="">
<span style="color: rgb(153, 153, 153);">
<b style="">Parc national des Écrins</b><br style="">
04 92 40 20 56 / 06 99 77 38 26<br style="">
<a href="http://www.ecrins-parcnational.fr/" style="color: rgb(153, 153, 153); font-weight: normal; text-decoration: none;" target="_blank">www.ecrins-parcnational.fr</a>
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</tbody></table><div style=""><br style=""></div></div><div style=""><br style=""></div><hr id="zwchr" style=""><div style=""><b style="">De: </b>"Michel Stuyts" <michel.stuyts@edegem.be><br style=""><b style="">À: </b>"Springfield Harrison" <stellargps@gmail.com><br style=""><b style="">Cc: </b>"qgis-user" <qgis-user@lists.osgeo.org><br style=""><b style="">Envoyé: </b>Vendredi 18 Mai 2018 08:44:01<br style=""><b style="">Objet: </b>Re: [Qgis-user] results Measure Tool vs. length()<br style=""></div><div style=""><br style=""></div><div style="">
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<p class="MsoNormal" style=""><span style="font-size: 11pt; font-family: "calibri",sans-serif; color: rgb(31, 73, 125);" lang="EN-US">$length gives the same result as length($geometry)</span></p>
<p class="MsoNormal" style=""><span style="font-size: 11pt; font-family: "calibri",sans-serif; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p class="MsoNormal" style=""><span style="font-size: 11pt; font-family: "calibri",sans-serif; color: rgb(31, 73, 125);" lang="EN-US"> </span></p>
<p class="MsoNormal" style=""><span style="font-size: 9pt; font-family: "calibri",sans-serif; color: rgb(31, 73, 125);">Michel<br style="">
<br style="">
</span><span style="font-size: 11pt; font-family: "calibri",sans-serif; color: rgb(31, 73, 125);"></span></p>
<p class="MsoNormal" style=""><b style=""><span style="font-size: 11pt; font-family: "calibri",sans-serif;" lang="NL">Van:</span></b><span style="font-size: 11pt; font-family: "calibri",sans-serif;" lang="NL"> Springfield Harrison [mailto:stellargps@gmail.com]
<br style="">
<b style="">Verzonden:</b> vrijdag 18 mei 2018 2:52<br style="">
<b style="">Aan:</b> Michel Stuyts <michel.stuyts@edegem.be><br style="">
<b style="">CC:</b> qgis-user <qgis-user@lists.osgeo.org><br style="">
<b style="">Onderwerp:</b> Re: [Qgis-user] results Measure Tool vs. length()</span></p>
<p class="MsoNormal" style=""> </p>
<p style="">Interesting and alarming observation.</p>
<p style="">And how do those results compare with output from the $length variable?</p>
<p style="">Cheers . . . . . Springfield<br style="">
Samsung Tab 4</p>
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<p class="MsoNormal" style="">On May 17, 2018 5:26 AM, "Michel Stuyts" <<a href="mailto:michel.stuyts@edegem.be" target="_blank" style="">michel.stuyts@edegem.be</a>> wrote:</p>
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<p class="MsoNormal" style=""><span style="" lang="EN-US">In the length() function QGIS uses the CRS unit of the layer to calculate the result. When I use for example a layer in a local CRS like EPSG:31370 or EPSG:5439
and a layer in EPSG:3857 (that all use meters as unit) the results are very different (+40% difference). Changing the project CRS makes no difference. When I check the length using the Measure Tool the results are very similar to the local CRS.</span></p>
<p class="MsoNormal" style=""><span style="" lang="EN-US"> </span></p>
<p class="MsoNormal" style=""><span style="" lang="EN-US">How can I measure the length of a line and use it as a label independent from the layer CRS and get results similar to the results of the Measure Tool?</span></p>
<p class="MsoNormal" style=""><span style="" lang="EN-US"> </span></p>
<p class="MsoNormal" style=""><span style="" lang="EN-US">Michel</span></p>
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