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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1807F7">My understanding is that you need to be in a projection where the units for that projection are in meters or feet before you will get accurate distance and
area measurements. Try using a UTM Zone that fits your area and the native values are in meters.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1807F7"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Qgis-us-user [mailto:qgis-us-user-bounces@lists.osgeo.org]
<b>On Behalf Of </b>David Noble<br>
<b>Sent:</b> Saturday, April 14, 2018 1:06 PM<br>
<b>To:</b> QGIS-us-user@lists.osgeo.org; Randal Hale<br>
<b>Subject:</b> Re: [Qgis-us-user] Question on area calculations<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">I had similar trouble with the distance measure tool. I don't have details at hand, but my project in Spokane, WA area seemed fine. New project in Coeur d'Alene, ID area was giving distances higher
than Google Earth and Bing. I took the car and drove some of the routes, noting mileage posts, comparing to my odometer. I already knew my odometer was reading about 10% high. I found my mapping in Idaho needed about 65% correction! I suspect difference in
projections and conversions when using different projection sources.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">My advice is to verify in the field. Don't rely on aerial scaling.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">I found I can adjust the map scale in the map composer. Under feature (individual?) property, the scale bar can be tweeked, using the inverse of the correction factor. I guess it makes the bar appear
longer, thus when compared to map, lengths measure shorter. This probably has no effect on area measurements, unfortunately. I had feet numbers overlapping each other, so I manually covered them and inserted aprox. mileage numbers over the scale bar.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">-Dave<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">On Friday, April 13, 2018, 6:14:59 AM PDT, Randal Hale <<a href="mailto:rjhale@northrivergeographic.com">rjhale@northrivergeographic.com</a>> wrote:
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A"><o:p> </o:p></span></p>
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<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">This has me puzzled. So I may have screwed up a very large job with incorrect acres and I was doing what I thought I needed to be doing. I'm probably doing this wrong - but
if I'm doing this wrong there's a large chance more people are doing the same. <o:p>
</o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">This is all in QGIS 3.0.1<o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">I have a forester who is working on a tract of land. There was a very hurried cruise they needed to do.
<o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">Data is in WGS84 and set to EPSG:2240 in QGIS.
<o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">Change the ellipsoid to None under project properties:
<o:p></o:p></span></p>
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<li class="MsoNormal" style="color:#26282A;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span style="font-size:10.0pt;font-family:"Helvetica","sans-serif"">using the identify button are 237 acres.
<o:p></o:p></span></li><li class="MsoNormal" style="color:#26282A;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span style="font-size:10.0pt;font-family:"Helvetica","sans-serif"">I get roughly 194 acres with the measure tool<o:p></o:p></span></li></ul>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">Changing the ellipsoid to GRS1980 (which QGIS Defaults to):
<o:p></o:p></span></p>
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<li class="MsoNormal" style="color:#26282A;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
<span style="font-size:10.0pt;font-family:"Helvetica","sans-serif"">I get 196 acres with the identify tool.
<o:p></o:p></span></li><li class="MsoNormal" style="color:#26282A;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo2">
<span style="font-size:10.0pt;font-family:"Helvetica","sans-serif""> I use the measure tool I get 194 acres<o:p></o:p></span></li></ul>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">I am assuming the 194/196 measurements are the exact same and due to human error on my part. PostGIS gives me 196 acres.
<o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">I guess (as I type this out) my correct course of action should be to leave the ellipsoid in GRS1980 and do my work - BUT - I thought I could drop back to none/planimetric
if I set the projection to EPSG:2240 in QGIS.<o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">Can anyone clue me in - I'm preparing for much yelling from the client in about 15 minutes as I was off about 40 acres which was a costly mistake. I'm not confident currently
in my area measurements using QGIS and I need to get confident. <o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A">Randy<o:p></o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A"><o:p> </o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A"><o:p> </o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A"><o:p> </o:p></span></p>
<p><span style="font-size:10.0pt;font-family:"Helvetica","sans-serif";color:#26282A"><o:p> </o:p></span></p>
<pre><span style="color:#26282A">-- <o:p></o:p></span></pre>
<pre><span style="color:#26282A">Randal Hale <o:p></o:p></span></pre>
<pre><span style="color:#26282A"><a href="mailto:rjhale@northrivergeographic.com" target="_blank">rjhale@northrivergeographic.com</a><o:p></o:p></span></pre>
<pre><span style="color:#26282A"><a href="https://www.northrivergeographic.com" target="_blank">https://www.northrivergeographic.com</a><o:p></o:p></span></pre>
<pre><span style="color:#26282A">(423)653-3611<o:p></o:p></span></pre>
<pre><span style="color:#26282A"><o:p> </o:p></span></pre>
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