Any software that computes Bookstein shape coordinates can get you
started. For example and using your notation, in the *old* morpheus
(http://www.morphometrics.org):
1) import your sample from your .tps file
2) Command: super Bookstein a b
This gives landmarks a,b coordinates 0,0 1,0 in all specimens. Now if
d(a,b) is 10cm, then any distances between the transformed landmarks X
10 will be in cm - just shift a decimal place. You could, for instance,
create a .mdt file containing the one line
dist "length" x y
Save the Bookstein'ed data (oh, I made Dr. B. a verb - "to Bookstein")
to morpheus format. Open that file in Morpheus and "Append" the one you
made above (all doable from the old Morpheus menu). Then, export the
data to a matrix, and the lengths (in decimeters) will be saved to the
matrix file.
You can also do the calc from the Bookstein'ed data easily in a spreadsheet.
Best, ds
I just checked out the procedure above with some sample data and it
worked as described. Note, the exported matrix will contain ALL of the
data - user variables, coordinates, etc. as well as measurements. -ds
morphmet wrote:
-------- Original Message --------
Subject: Evaluating body length using tps landmark coordinates
Date: Tue, 10 Feb 2009 05:43:02 -0800 (PST)
From: Henrik Kusche <[email protected]>
To: morphmet <[email protected]>
Dear all,
using tpsdig2 I created an extensive tps-dataset that encodes body
shape in a fish species complex in terms of pixel units. Instead of
using the ruler tool in tpsdig2 I placed two additional landmarks,
(let´s say LM a and LM b respectively) beyond the fish body whose
distance on the original photo is equal to 10 centimeters (a ruler was
photographed below the fish).
Among others I have two landmarks LM x and LM y ( LM x at the tip of
the snout and LM y at the base of the tail fin respectively) that
define the body length of the fish.
My problem is that I would like to use the 2 "10cm-scaling landmarks"
thus LM a and LM b as a length reference that permit me to assess the
distance between LM x and LM y, thus the body length of the fish.
I would be very happy if someone of you could help me with this problem.
Best wishes, Henrik
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