-------- Original Message -------- Subject: RE: error in digitising landmarks Date: Thu, 3 Feb 2011 16:05:36 -0500 From: Carmelo Fruciano <[email protected]> To: [email protected] morphmet <[email protected]> ha scritto:
-------- Original Message -------- Subject: RE: error in digitising landmarks Date: Thu, 3 Feb 2011 15:00:52 -0500 From: Garrido-Varas, Claudia <[email protected]> To: [email protected] <[email protected]> Dear Carmelo, Thank you very much for your email. I will try what you say. Yes, I said reliable because the landmarks that I am using have been chosen by myself, so, I want to test them and want to test my personal error, and see that maybe I should use only the ones that have the least error.
Well, the problem there is how you do set up a threshold to remove certain landmarks and keep others. In the "exploratory" procedure I suggested the decision of which landmarks should be removed is subjective (nonetheless, it can be useful to have a look at those plots)
Once that I know I have picked up the proper landmarks I will compare the shape change in different individuals, see if sex has an impact and look at bilateral asymmetry. Another thing that I would like to ask is if I need to have a scale, because in the morhoJ program one never needs to input which pair of landmarks are the ones of the scale, I get very confused in how centroid size can be computed if I don't give the scale.
If you performed the digitization with TpsDig2, you can set up the scale from there, using the appropriate part of the "Image Tools" option (refer to the program manual, it's explained very well there). If you save your data as a TPS file, this adds a SCALE line for each specimen (assuming that you entered scale for each specimen), which you can check by opening the TPS file with a text editor (such as Windows Notepad). Then, if you wish to use MorphoJ you can import the TPS containing the scale as a new dataset and perform the Procustes superimposition there (calculating also centroid size; take a look at the program guide that is online). In your particular case, it sounds not particularly important to have a scale and calculate centroid size because your dataset is currently made of only one specimen and you are probably going to have a look at plots of landmarks after superimposition. Moreover, using a single picture the presence of the scale is not so important (it is important when you deal with multiple specimens and then one picture is slightly different than the next one so you can compute centroid size values that are in the same units for all the specimens). All the best Carmelo -- Carmelo Fruciano Dipartimento di Biologia University of Catania Tel. +39 095 7306023 Cell. +39 349 5822831 e-mail [email protected] ---------------------------------------------------------------- Universita' di Catania - A.P.Se.Ma. Servizio di Posta Elettronica
