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<p>Good afternoon QGIS People <br>
</p>
<p>I received a question on RMSE errors in georeferencer and after
talking to Ethan about it I realized I have no clue what I'm
talking about. How would we go about calculating an RMSE for a
rectified image in QGIS? <br>
</p>
<p>I've cc'd ethan on this so he can chime in also. <br>
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<p>Thanks <br>
</p>
<p>Randy<br>
</p>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Subject:
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<td>Georeferencer Plugin Help - QGIS</td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Date: </th>
<td>Fri, 2 Oct 2020 15:27:13 +0000</td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">From: </th>
<td>Ethan Cissell <a class="moz-txt-link-rfc2396E" href="mailto:ecissell@bio.fsu.edu"><ecissell@bio.fsu.edu></a></td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">To: </th>
<td><a class="moz-txt-link-abbreviated" href="mailto:info@northrivergeographic.com">info@northrivergeographic.com</a>
<a class="moz-txt-link-rfc2396E" href="mailto:info@northrivergeographic.com"><info@northrivergeographic.com></a></td>
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<span style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);
font-family: GillSans;" class="">Hi Randal,</span>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
<br class="">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
I have a question about the usage and outputs of the
Georeferencer Plugin in QGIS, and thought, given your expertise,
you might be able to directly help, or point me in the right
direction.</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
<br class="">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
I am a Ph.D. candidate in Ecology and Evolution at Florida State
University applying spatial techniques to study the dynamics of
benthic cyanobacterial mats on coral reefs. This past summer, I
photographically tracked individual cyanobacterial mats in which
I had placed plastic stakes as ground control points for later
image rectification. I am trying to essentially create image
stacks, so that I can parameterize a generalized additive mixed
effects model that accounts for the inherent spatial
autocorrelation and includes a parameter with occupation at the
previous time-point explicitly included to hopefully model the
population dynamics of this system.</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
<br class="">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Thus, a quantitative understanding of the error in my alignment
is absolutely critical to the downstream conclusions (especially
for informing my resampling to larger grid size to account for
error in my alignments).</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
I am using QGIS for obtaining all raw data from these photos
(scaling, rectification, classification, resampling), but I am
stuck at the rectification step. I am using the Georeferencer
plugin to accomplish my alignments, but I have received mixed
advice on how to interpret the residuals output on the GCP table
in the Georeferencer window (screenshot below). The
documentation for this plugin seems to indicate that the far
right column (Residual) is actually a per GCP RMS error.</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
<br class="">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Can you tell me how to interpret these errors/how to obtain a
total RMSE error for the image alignment (i.e. not just per GCP
error, but total error for each image)? I have been told to sum
all of the values from the residuals column and take the square
root of that raw summation. Is this correct?</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
<br class="">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Many thanks in advance. I apologize for the lengthy email, but I
wanted to establish the motivations for this project so that you
would have more context for the goals of the alignment.</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Any and all help here is greatly appreciated.</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
<br class="">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
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</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
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<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
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<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Best,</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
<br class="">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Ethan C Cissell</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Ph.D. Candidate - McCoy Lab</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
National Science Foundation Graduate Research Fellow</div>
<div class="" style="caret-color: rgb(0, 0, 0); color: rgb(0, 0,
0); font-family: GillSans;">
Florida State University</div>
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