Hi, > No no, to take the average of the areas is not the same as take the average > of the coordinates, because the areas depend quadratically on linear > distances. An average of the areas would not necessarily represent a surface > at the middle, most likely representing an (invisible) surface that would be > closer to the white in some places and closer to the pial in others, > depending on local folding. > Hope this helps!
yes - that helps and clarifies things. Thank you all for your help and patience, Boris On 2011-05-12, at 11:57 PM, Anderson Winkler wrote: > Hi Boris, > >> For now I am taking the geometric average between pial and white surface >> coordinates. >> Is that the right way to do it, or is there a more precise way? > > To obtain a surface that lies in the geometric middle between white and pial > surfaces, it is correct to take the average of the coordinates. This surface > is not guaranteed to coincide with any biologically meaningful cortical > layer, but it has advantages over pial or white for not > over/under-representing gyri or sulci. > >> Also: If I decided to represent the stuff on the mid-surface, would it then >> also make sense to also take the average of pial.avg.area.mgh >> white.avg.area.mgh as the area estimation at each vertex? > > No no, to take the average of the areas is not the same as take the average > of the coordinates, because the areas depend quadratically on linear > distances. An average of the areas would not necessarily represent a surface > at the middle, most likely representing an (invisible) surface that would be > closer to the white in some places and closer to the pial in others, > depending on local folding. > > Hope this helps! > > All the best, > > Anderson
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