abstract = "We describe a progression of solutions to a difficult
object detection problem, that of locating landmarks in
X-Rays used in orthodontic treatment planning. In our
first formulation an object detector was a genetic
program whose inputs were a number of attributes
computed from a scanning window. We used a rich
function set comprising + - times divide min; max;
ifthenelse. Experimentation with different function
sets revealed that using the function set + - gave
detectors that were almost as accurate. Such detectors
are essentially a linear combination of attributes so
we also implemented a parameter optimisation solution
with a particle swarm optimiser. Contrary to
expectation, the PSO detectors are more accurate and
smaller than the GP ones. Our analysis of the reasons
for this reveals that (1) the PSO approach involves a
considerably smaller search space than the GP approach,
(2) in the PSO approach there is a 1-1 mapping between
genotype and phenotype while in the GP approach this
mapping is many-1 and many semantically equivalent
potential solutions are evaluated, (3) the fitness
landscape for PSO is a good one for search in that
solutions are distributed in areas of high fitness that
are easy to locate while the GP landscape is much more
difficult to characterise and areas of high fitness
more difficult to find.",
notes = "WCCI 2006 - A joint meeting of the IEEE, the EPS, and
the IEE.