-------- Original Message -------- Subject: Re: image taking for geometric morphometrics Date: Tue, 6 Sep 2011 10:32:33 -0400 From: Carmelo Fruciano <[email protected]> To: [email protected] CC: [email protected] morphmet <[email protected]> ha scritto:
-------- Original Message -------- Subject: image taking for geometric morphometrics Date: Mon, 5 Sep 2011 19:18:07 -0400 From: Darren Parsons <[email protected]> To: <[email protected]> Hi there, I am just starting out with geometric morphometrics, so was hoping someone could point me towards any documents that could get me started. My specific query is around the image taking process. This is because I may not be able to analyse the images for some time (images will be of fish ~ 40 cm in length). So, for now, I would like to ensure that I take images that will allow me to do 2D analysis later on. Is there a document/book/previous string of postings that outlines the best image taking process/equipment in simple terms? I have "Zelditch, Geometric morphometrics for biologists : a primer" on order from my library?
Dear Darren, as far as I remember, there is no complete guide for your particular case. However, assembling suggestions from multiple sources you will easily find your own way of taking pictures. The MORPHMET archives (see http://www.morphometrics.org/morphmet.html ) contain a few discussions which you might find useful. The Zelditch book you cite also contains useful tips to take good pictures. Having worked with dead or anaesthesized fish, I have found very useful a copy stand. I know that people often use a tripod but, in my case, I preferred a copy stand. Another useful thing is to put the camera relatively distant from the specimen, to minimize due to the effect of parallax (see Mullin & Taylor 2002 Computers in Biology and Medicine 32:455?464). One common problem with fish is dorso-ventral arching. The extent of the problem depends on the shape of the fish. While it can be accounted for in analyses which follow the data gathering phase (see for example Valentin et al 2008 Journal of Fish Biology 73:623?638), I believe that one should try to obtain pictures where fish are not very arched. A trick (which I have used with smaller fish, I learned it from Windsor Aguirre) is to run a needle on a side of the body to keep the fish straight. However, I don't know how useful this trick would be on a 40 cm fish (personally, with trouts, which in some cases were that big, I decided not to use it). With fish this big I would also be concerned about lateral arching (that is, the head and the tail lie on a different plane relative to the side of the body) and different degrees of thickness (if you decide to use both landmarks along the midline of the body, such as on the dorsal fin and landmarks on the side, such as on the pectoral fin). I suppose that everyone comes with a personal solution for this kind of problems, a solution which can depend on the studied species... Optics from the camera can introduce a certain degree of distortion on the outer portion of the field (see the Zelditch book again) but I'm said that often for upper-scale cameras there are software "filters" which allow to correct for this problem (but I have never used them)... Well, just my two cents... Carmelo -- Carmelo Fruciano Dipartimento di Biologia University of Catania Tel. +39 095 7306023 Cell. +39 349 5822831 e-mail [email protected] http://www.fruciano.it/research/ ---------------------------------------------------------------- Universita' di Catania - A.P.Se.Ma. Servizio di Posta Elettronica
