			Home About us Contact

Shape Measurement (shape + measurement)

Distribution by Scientific Domains

Physics and Astronomy	66%

Selected Abstracts

Evaluation of Digital Image Discretization Error in Droplet Shape Measurement Using Simulation

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5-6 2009
Sina Ghaemi
Abstract Droplet shape measurement using image based techniques can be conducted using shape parameters which consist of a number of geometric features of a droplet image. The accuracy of calculating these shape parameters and their capability in revealing shape deviation is considerably affected by the discretization of the image with a camera CCD. In this paper, a simulation of digital images is conducted to investigate the error caused by image discretization. The effect of this error on calculating area, perimeter, and also a selected number of shape parameters are investigated. Digital images of circular and elliptical discs at different image/pixel size ratio and locations relative to the pixel grid have been generated to simulate the projected view. Results show that the shape parameters demonstrate different levels of sensitivity to the desirable factor of shape deviation and the undesirable factor of image discretization. A "clearance factor" has been suggested and used to rank the shape parameters based on their compensation between sensitivity to shape deviation and image discretization. [source]

Shape measurement using pulsed optical holography , Fast and precise shape measurement of moving objects

LASER TECHNIK JOURNAL, Issue 1 2006
Susanne Frey Dr.
The starting point for the development of a new shape measurement system was the request of surgeons working in the field of cranio-facial and reconstructive surgery for an improved system for precise facial measurement. For the planning and documentation of surgical interventions, information on the bone structure of the patient is needed, which is imaged by computer tomography (CT). In particular in facial surgery it is vital to the patient, that not only the functionality of the face is given, but also the appearance of the patient is restored. To account for this aspect in the planning and evaluation of surgery, the outer appearance of a patient has to be documented, hence a surface model of the face has to be generated. [source]

Bayesian galaxy shape measurement for weak lensing surveys , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
Application to simulations
ABSTRACT In this paper, we extend the Bayesian model fitting shape measurement method presented in Miller et al., and use the method to estimate the shear from the Shear TEsting Programme simulations (STEP). The method uses a fast model fitting algorithm that uses realistic galaxy profiles and analytically marginalizes over the position and amplitude of the model by doing the model fitting in Fourier space. This is used to find the full posterior probability in ellipticity. The shear is then estimated in a Bayesian way from this posterior probability surface. The Bayesian estimation allows measurement bias arising from the presence of random noise to be removed. In this paper, we introduce an iterative algorithm that can be used to estimate the intrinsic ellipticity prior and show that this is accurate and stable. We present results using the STEP parametrization that relates the input shear ,T to the estimated shear ,M by introducing a bias m and an offset c: ,M,,T=m,T+c. The average number density of galaxies used in the STEP1 analysis was 9 per square arcminute, for STEP2 the number density was 30 per square arcminute. By using the method to estimate the shear from the STEP1 simulations we find the method to have a shear bias of m= 0.006 ± 0.005 and a variation in shear offset with point spread function type of ,c= 0.0002. Using the method to estimate the shear from the STEP2 simulations we find that the shear bias and offset are m= 0.002 ± 0.016 and c=,0.0007 ± 0.0006, respectively. In addition, we find that the bias and offset are stable to changes in the magnitude and size of the galaxies. Such biases should yield any cosmological constraints from future weak lensing surveys robust to systematic effects in shape measurement. Finally, we present an alternative to the STEP parametrization by using a quality factor that relates the intrinsic shear variance in a simulation to the variance in shear that is measured and show that the method presented has an average of Q, 100 which is at least a factor of 10 times better than other shape measurement methods. [source]

Bayesian galaxy shape measurement for weak lensing surveys , I. Methodology and a fast-fitting algorithm

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007
L. Miller
ABSTRACT The principles of measuring the shapes of galaxies by a model-fitting approach are discussed in the context of shape measurement for surveys of weak gravitational lensing. It is argued that such an approach should be optimal, allowing measurement with maximal signal-to-noise ratio, coupled with estimation of measurement errors. The distinction between likelihood-based and Bayesian methods is discussed. Systematic biases in the Bayesian method may be evaluated as part of the fitting process, and overall such an approach should yield unbiased shear estimation without requiring external calibration from simulations. The principal disadvantage of model fitting for large surveys is the computational time required, but here an algorithm is presented that enables large surveys to be analysed in feasible computation times. The method and algorithm is tested on simulated galaxies from the Shear TEsting Programme (STEP). [source]

Evaluation of Digital Image Discretization Error in Droplet Shape Measurement Using Simulation

Characteristics, head shape measurements and developmental delay in 287 consecutive infants attending a plagiocephaly clinic

ACTA PAEDIATRICA, Issue 9 2009
BL Hutchison
Abstract Aim:, To describe the characteristics, developmental status and severity of head shape deformation in infants presenting to a plagiocephaly clinic. Methods:, Head shape was measured and neck function assessed in 287 consecutive infants presenting to a plagiocephaly outpatient clinic. Information was obtained on demographic and obstetric factors, plagiocephaly history and current positioning strategies. Development was assessed by the Ages and Stages Questionnaire (ASQ). Results:, After clinical examination, craniosynostosis was suspected in seven infants (2%) and a skull computed tomography (CT) scan was performed; five showed suture abnormalities. Fifty-eight percent of cases had a history of limitation of neck function; this was more likely in plagiocephalic infants than brachycephalic infants. Males, firstborn infants, instrument-delivered infants, supine sleep position and right-sided flattening were predominant. One or more delays on the ASQ were seen in 36% of infants. Conclusion: Physical examination of infants with head shape deformities is essential in order to rule out craniosynostosis. Infants with deformational plagiocephaly frequently have neck muscle dysfunction. We postulate that the higher than expected number of developmental delays may be related to the effects of supine sleep position, low or variable tone, lower activity levels, male gender and neck muscle dysfunction. [source]