-------- Original Message -------- Subject: How to test landmarking accuracy Date: Thu, 20 Oct 2011 11:10:30 -0400 From: Wechsler, Samuel <[email protected]> To: [email protected] <[email protected]> Dear all I am completely new to the morphometrics business. For my master thesis I work with pictures of brown trout. I would like to check how accurate I work when a) I set the landmarks and b) when I take pictures. To check this I landmarked three different sets of pictures: 1^st set: 5 times exactly the same picture (to test how accurately I can landmark) 2^nd set: 5 times exactly the same fish on 5 pictures taken on different days (to test how accurately I take photographs) 3^rd set: 5 different fish I am looking for a statistical measure that can inform me about the spread of my landmarks around their respective average (something equivalent to standard deviation or alike). When I do the procrustes fit in MorphoJ the results section (attached below) provides “Procrustes sums of squares”. Now finally here my questions: 1)What are these Procrustes sums of squares exactly? Are they an overall sum of all squared procrustes distances over every landmark and every observation (1 observation = coordinates from 1 picture)? 2)Can the Procrustes sums of squares be converted/standardized to a measure that can be compared between sets of pictures with differing number of observations? Thank you for your help. Kind regards Sämi PS: Below an example result output from morphoJ Dataset 'NM007 (5x)' 16 landmarks in 2 dimensions. The dataset contains 5 observations, of which 5 are included for analyses. Average shape: Lmk. Axis 1 (x) Axis 2 (y) 1 -0.29489099 0.01139803 2 -0.26145670 0.02011783 3 -0.24846114 0.02003904 4 -0.23435917 0.02014906 5 -0.22792309 -0.03741346 6 -0.12578189 -0.00296614 7 -0.12529903 0.07369970 8 -0.12574654 -0.07027571 9 -0.14574592 -0.04920278 10 0.04206763 0.08215905 11 0.28577462 0.05461450 12 0.35694734 0.04214234 13 0.40457048 0.00679023 14 0.35382919 -0.02944051 15 0.24278591 -0.06530739 16 0.10368929 -0.07650380 Procrustes sums of squares: 0.0016642169841469471 Tangent sums of squares: 0.0016636098057431449 Data matrices in this dataset: - NM007 (5x), raw data - NM007 (5x), centroid size - NM007 (5x), Procrustes coordinates
