Hi all, The answer to Pablo Jarrin's question about how to rotate a set of landmark configurations is simple; all you want to do is "rotate" the coordinate set 90 degrees prior to computing symmetrized shapes in BigFix. As Oyvind suggested this can be done easily in Excel. Let's say you want Ynew = Xold, Xnew = -Yold (up becomes left and down becomes right): 1. Open your tps format file (from TPSdig or CoordGen) in Word, delete any spaces in control lines (lm=... etc.). 2. Save and open in Excel. 3. Copy the first column (Xold and control lines) into the third column. 4. Multiply the second column (Yold) by -1. 5. Cut and paste the control lines (LM= etc) so they start in the second column and read correctly. 6. Delete the first column (Xold). The new first column (Xnew) is the negative of the original second column (-Yold), and the new second column (Ynew) is the original first column (Xold). 7. Save as a text file.
To rotate in the opposite direction, Up to right, all is the same except step 4. In the new step 4, you multiply the third column by -1, not the second column. Now the result is Xnew = Yold, Ynew= -Xold. This will allow you to reflect and average in BigFix (or you could do that in Excel, also). With regard to the question of visualization, yes, the correct visualization of analyses based on the symmetrized half-skull, is that half skull. The problem is that Procrustes superimposition treats the midline points the same as any other, and as Bookstein once pointed out "happily" rotates the shapes. This sometimes produces disconcerting pictures in which the midline appears to rotate and deformations appear to produce asymmetry. Generation of symmetrical configurations is one way to avoid these visualization issues, by mirroring the configuration of lateral landmarks. The result is superimpositions that slide, but don't rotate. It is important to understand that these pictures are strictly for visualization purposes; if they don't help you to understand and illustrate the results of analyses on the half skull, don't use them. ---------- Don Swiderski University of Michigan ph: 734-763-9613 fax: 734-615-8111 [EMAIL PROTECTED] -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
