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<p>Hi,</p>
<p>Start with finding a background map or a project CRS that is
similar to your old maps. That takes a bit of guessing. Then
select the Helmert method in the transformation method. All you
need is 2 GCP (ground control points). If you add more, you will
see how you map is warped and how points drift. Once you are
happy with the results, then change the method to Thin Plate
Spline and you can start adding GCP and testing the results. That
will and can really warp the map so be careful with this method.
<br>
</p>
<p>Nicolas<br>
</p>
<div class="moz-cite-prefix">On 2021-08-25 1:26 p.m., Firstname
Lastname wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAAyYZQLTvue1y8ZJGO0ZV_whc-=2NqdhnzXe+xMQTrznoqCKFA@mail.gmail.com">
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<div>hello</div>
<div>i am trying to do some basic georeferencing. i have been
using the georeferencing tool and i have been following the
workflow suggested on youtube files using the georeferencing
tool </div>
<div>i have tried three different maps of new and old vintage.
i have tried to keep it simple with 4 points control points
and have used as many as 10 points. when i apply the
georeferencing, my maps are not calibrating. even the control
points end up 400-600 m. of off the true coordinates. Any
suggestions that might help fix this. </div>
<div>for reference, i used the epsg 3857 CRS </div>
-- <br>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr">Byron Veilleux, MSc. P.Geo
<div>Conjugate Geologic Services Limited</div>
<div>Calgary, Alberta Canada</div>
<div><a href="mailto:byron@conjugategeo.com" target="_blank"
moz-do-not-send="true">byron@conjugategeo.com</a></div>
<div>Cell:4037108414</div>
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<pre class="moz-signature" cols="72">--
Nicolas Cadieux
<a class="moz-txt-link-freetext" href="https://gitlab.com/njacadieux">https://gitlab.com/njacadieux</a></pre>
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