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: 
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0149313 
<http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0149313>
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. 

Best wishes, 
Sonja Windhager
—
Dr. Sonja Windhager
Department of Anthropology, University of Vienna (Lecturer) and
Department of Theoretical Biology, University of Vienna (Postdoc)
Althanstrasse 14, 1090 Wien, Austria
http://homepage.univie.ac.at/sonja.windhager/ 
<http://homepage.univie.ac.at/sonja.windhager/>
http://theoretical.univie.ac.at/people/windhager/ 
<http://theoretical.univie.ac.at/people/windhager/>





> 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!
> 
> Anderson
> 
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