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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Hi Dean,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Do you use existing parameters for the Helmert transformation or do you estimate parameters yourself?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">The quality and residuals of estimated parameters depends on the quality and distribution of the coordinates used for the estimation. For a Helmert transformation between a triangulated and a GNSS
data set of an entire country of some hundreds of kilometres across, residuals over 1 metre are not uncommon. For two datasets of permanent GNSS stations of a small area, residuals can be under 1 centrimetre.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Kind regards, Jochem
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b>Van:</b> PROJ <proj-bounces@lists.osgeo.org> <b>Namens </b>
Dean Howell<br>
<b>Verzonden:</b> woensdag 20 maart 2019 06:01<br>
<b>Aan:</b> proj@lists.osgeo.org<br>
<b>Onderwerp:</b> [PROJ] Helmert transform<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="color:blue">Hello all,<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="color:blue">We have a project that is using the helmert transformation and we are trying to get an understanding of what level of residuals is acceptable and how we interpret the results.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:blue"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:blue">If anyone has experience in using the helmert transformation, I would be interested in your feedback.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:blue"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:blue">Regards<br>
<br>
Dean Howell</span><o:p></o:p></p>
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