Dear Eli,
I'd say that it depends on what you want to do.
If quantifying asymmetry is one of your aims, then of course you must
have landmarks on both sides.
If not, I'd tend to say that it's better to have the bilateral landmarks
and then decide whether or not to 'symmetrize' the data.
However, even in this second case, as I suggested with an example in a
paper which should be soon out in Syst. Biol., there might be cases when
you might decide to landmark just one side to save time and money and
maximize sampling during data collection. Then, often, by simply
reconstructing the side with no landmarks by mirror-reflection, you
might get a better approximation of the total configuration you would
have had by landmarking both sides.
There might be also cases when you really want to measure just one side
because your question is specific to that side, but I've never found one
such case in the literature.
To symmetrize the data in MorphoJ you just need to:
1) load them as data with object symmetry;
2) do the Procrustes superimposition (and check that MorphoJ is
'guessing' the correct pairs of bilateral landmarks);
3) save size and the symmetric component (export from the file menu);
4) restore size by multiplying the symmetric shape coordinates by the
centroid size of the corresponding individual.
Of course, if you do all your analyses in MorphoJ, you just need to
select each time only the symmetric component.
Cheers
Andrea
On 05/07/16 16:36, Elahep wrote:
Dear all,
I have got quite confused about object symmetry! If analyzing symmetry
is not our purpose is this necessary to do symmetrizing procedure for
the data that have bilateral symmetry?
I have seen some people choose only one side of the bilaterally
symmetric object to study its shape variation (for example between
geographic areas). In this case is this better to put landmarks in
both sides of the midline or considering just one side is enough? If I
want to do the symmetrizing how can I do it with tps series or Morphoj?
Any help would be appreciated!
Eli
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