[Qgis-user] Fwd: Georeferencer Plugin Help - QGIS

[Alexis R.L.]

Greetings,

The relevant code is located here
https://github.com/qgis/QGIS/blob/master/src/app/georeferencer/qgsleastsquares.cpp

Hope this helps.

Alex


Le lun. 2 nov. 2020 à 16:18, Randal Hale <rjhale at northrivergeographic.com>
a écrit :

> Good afternoon QGIS People
>
> 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?
>
> I've cc'd ethan on this so he can chime in also.
>
> Thanks
>
> Randy
>
>
> -------- Forwarded Message --------
> Subject: Georeferencer Plugin Help - QGIS
> Date: Fri, 2 Oct 2020 15:27:13 +0000
> From: Ethan Cissell <ecissell at bio.fsu.edu> <ecissell at bio.fsu.edu>
> To: info at northrivergeographic.com <info at northrivergeographic.com>
> <info at northrivergeographic.com>
>
> Hi Randal,
>
> 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.
>
> 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.
>
> 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).
> 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.
>
> 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?
>
> 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.
> Any and all help here is greatly appreciated.
>
>
>
>
> Best,
>
> Ethan C Cissell
> ——————————————
> Ph.D. Candidate - McCoy Lab
> National Science Foundation Graduate Research Fellow
> Florida State University
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