Re: Supplier of measuring devices (fwd)

From
Date
The request:
>        Someone here who is working with dinosaur eggshells (trying to
>measure the radius of curvature) is looking for a Geneva lens measure (he
>isn't sure about this--says maybe it refers to a method) or a surface
>gauge.  I don't have any catalogs that offer those sorts of things.  Can
>you provide the name and address of a suitable vendor?

These tools may be unknown because such problems can be solved with image
analysis. Most systems have an edge detection and measurement algorithm
that would measure the curvature. Our systems returns the center of a
fitted circle (and its radius) and a measure of curvature for an edge
segment that was selected by the user. I preferred to perform an outline
detection of the object and to store the pixel coordinates for each point
on the outline. With this data it is easy to compute the curvature (as an
angle) for at least 3 pixel intervals with a spreadsheet program. This data
will be noisy (because it is maximum spatial resolution) but averaging
along the outline is always possible and computations can be done for
larger outline segments. Fourier descriptors may also be used as a measure
of curvature (or its variability). See brief report on an application to
inoceramid bivalves on http://www.erdw.ethz.ch/~heinz/INO.html

A personal computer-based image processing system and a camera should be
available somewhere at a university (often used by engineers for quality
control, or by biologists). If not, please contact me offline. With a few
eggshells a paleontologist can not bother the friendly colleagues too much.
The measurements are quickly done if the margin of the shell can be viewed
next to a high contrast background. I guess dinosaur eggshells will be even
fun for people from outside paleontology.

Heinz Hilbrecht



Address:

Heinz Hilbrecht
Geological Institute
ETH Zentrum
Sonneggstr. 5
CH-8092 Zuerich
Switzerland

phone:  ++41-1-6323676
fax:      ++41-1-6321080
WWW: http://www.erdw.ethz.ch/~heinz/
e-mail:  Hilbrecht@erdw.ethz.ch