Dear Colleagues on Biomch-L:

I am currently writing a paper on the role of the light refraction at the
water/air interface on the accuracy of the space reconstruction in the
underwater motion analysis using 2-D and 3-D DLT. I've read some papers
dealing with 3-D underwater motion analysis of the Olympic swimmers using the
DLT, underwater panning videography, shape of the face of the waterproof
camera housing, etc. Although people seem to already use the DLT in the
underwater motion analysis quite a bit, I haven't found any paper dealing
with the nature of the refraction and the potential problems due to the

As you know, the DLT is based on the so-called 'collinearity condition' which
requires the camera node, object and image to form a straight line. But this
rule is violated in the underwater motion analysis due to the refraction.
Some investigators have reported studies using the DLT but without telling
the magnitude of the calibration error. Some investigators tried to connect
the above-water space and the below-water space using a technique which seems
to have potential problems.

Are there any in-depth studies reported on the nature and role of the
refraction in the underwater motion analysis which are out of my reach? If
any, they will be most valuable for my paper. I also invite your comments on
this matter.

Looking forward to hearing from you,

Young-Hoo Kwon, Ph.D.
Senior Researcher
Korea Sport Science Institute
223-19 Gongneung-Dong
Seoul, 139-242

Phone: +82-2-9709-555
Fax: +82-2-9709-502