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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Thank you very much for the explanation.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">When I use
<i>length(transform($geometry,layer_property(@layer_id,'crs'),'EPSG:31370'))</i> in Belgium the results are very similar to the result of the Measure Tool, but if use this expression in New York the result is different from the result of the Measure Tool.
It is the other way around if I use <i>length(transform($geometry,layer_property(@layer_id,'crs'),'EPSG:102316')).</i> What kind of projection does the Measure Tool use to calculate a length? Because the results of the Measure Tool seem to be very similar
to local projections.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Michel<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="NL" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Van:</span></b><span lang="NL" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Julien Guilloux [mailto:julien.guilloux@ecrins-parcnational.fr]
<br>
<b>Verzonden:</b> vrijdag 18 mei 2018 11:01<br>
<b>Aan:</b> Michel Stuyts <michel.stuyts@edegem.be>; Springfield Harrison <stellargps@gmail.com>; qgis-user <qgis-user@lists.osgeo.org><br>
<b>Onderwerp:</b> Re: [Qgis-user] results Measure Tool vs. length()<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">Hi Michel,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">Never use epsg 3857 for measurement beacuse it is not a "projection"...
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">this "pseudo projection mercator" 3857, called often "Popular Visualisation" is pseudo.... Because only use for visualization applications.
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">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)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">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....<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">best regards,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">Julien<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">have a look on :<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black">http://spatialreference.org/ref/sr-org/6864/<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="border:solid windowtext 1.0pt;padding:0cm"><img width="100" height="100" id="_x0000_i1026" src="cid:image001.jpg@01D3EE9D.A91E5590" alt="Afbeelding verwijderd door afzender."></span><o:p></o:p></p>
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<p class="MsoNormal"> <span style="border:solid windowtext 1.0pt;padding:0cm"><img width="100" height="100" id="_x0000_i1027" src="cid:image001.jpg@01D3EE9D.A91E5590" alt="Afbeelding verwijderd door afzender."></span><o:p></o:p></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Julien-Pierre GUILLOUX</span></b><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><br>
Chargé de mission Eau, Forêt, Natura 2000, coordinateur des porter-à-connaissance<br>
<br>
<b><span style="color:#999999">Parc national des Écrins</span></b><span style="color:#999999"><br>
04 92 40 20 56 / 06 99 77 38 26<br>
<a href="http://www.ecrins-parcnational.fr/" target="_blank"><span style="color:#999999;text-decoration:none">www.ecrins-parcnational.fr</span></a>
</span><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:black"><o:p> </o:p></span></p>
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