Dear Anderson Feijo,
I assume that the difference is not a matter of scaling (that could be
addressed with the Procrustes superimposition), but one of optical distortions
caused by the lens.
This paper exemplifies this for different lenses:
Likewise, to minimize optical distortions with a small focal length you would
need to enlarge the distance more than sharpness allows.
If you have the possibility to use a 3D Scanner or photogrammetry, you could
then set the viewing setting to “infinity” instead of mimicking a rather short
lens for digitization.
Dr. Sonja Windhager
Department of Anthropology, University of Vienna (Lecturer) and
Department of Theoretical Biology, University of Vienna (Postdoc)
Althanstrasse 14, 1090 Wien, Austria
> On 29 Dec 2017, at 10:18, Anderson Feijo <andefe...@gmail.com> wrote:
> Hi everyone,
> I am starting a new project using GM which I will work with groups with
> different sizes (e.g., rodents and small carnivores). I would like to find a
> way to use the whole dataset in the analyses, instead of perform set of
> analyses for each sized group. So, I did a test using one skull and place the
> camera in two different distances to the object (~15 cm and ~30 cm). My
> expectation was after scaling (using tpsDig) I wouldn´t have any meaningful
> difference. But I got two clear groups that were statistically different. So,
> my question is how can I combine 2D landmarks based on photos taken from
> different distances of the camera to the object. I have attached here the tps
> file (10 copies of the same skull, five at ~15cm and five at ~30cm). I would
> be very grateful for any suggestion.
> All the best and Happy 2018!
> MORPHMET may be accessed via its webpage at http://www.morphometrics.org
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