Stereoscopic 3D display with color interlacing improves perceived depth

Temporal interlacing is a method for presenting stereoscopic 3D content whereby the two eyes' views are presented at different times and optical filtering selectively delivers the appropriate view to each eye. This approach is prone to distortions in perceived depth because the visual system can interpret the temporal delay between binocular views as spatial disparity. We propose a novel color-interlacing display protocol that reverses the order of binocular presentation for the green primary but maintains the order for the red and blue primaries: During the first sub-frame, the left eye sees the green component of the left-eye view and the right eye sees the red and blue components of the right-eye view, and vice versa during the second sub-frame. The proposed method distributes the luminance of each eye's view more evenly over time. Because disparity estimation is based primarily on luminance information, a more even distribution of luminance over time should reduce depth distortion. We conducted a psychophysical experiment to test these expectations and indeed found that less depth distortion occurs with color interlacing than temporal interlacing.

A three-dimensional evaluation of Māori and New Zealand European faces

OBJECTIVE

Māori patients are often inappropriately treated using Caucasian norms, despite obvious differences in facial morphology. There is currently very little data concerning the nature and/or magnitude of these differences in facial features. The objective of the present study was therefore to evaluate the facial features of Māori and New Zealand (NZ) Europeans.

METHODS

Two convenience samples of 30 Māori and 30 NZ Europeans, evenly matched for age and gender, were recruited from amongst students of the University of Otago, New Zealand. Using a 3D white-light scanner, 12 facial scans were taken of each participant, which were then merged to form a single 3D image of the face. Prior to scanning, round markers were fixed to the skin in order to facilitate the localisation of facial anthropometric points and from which vertical, sagittal, and transverse measurements were assessed from the 3D facial image. Univariate and multivariate analyses of variance were used to test for differences between the two groups before and after adjusting for body mass index (BMI).

RESULTS

Significant differences were found in vertical, sagittal, and transverse facial dimensions, before and after adjusting for BMI. The overall face of Māori was significantly larger than that of NZ Europeans, although the facial proportions were generally similar. However, Māori had a broader face, more anterior position of the chin and reduced facial convexity in comparison with NZ Europeans (p < 0.01).

CONCLUSION

Māori have markedly different sagittal facial features compared with NZ Europeans. These distinctive features may reflect important differences in environmental and genetic influences between the two populations. The findings from the present study may assist the clinician in the treatment planning and assessment of facial dysmorphology in these ethnic groups.

Radiation-free spinometry adds to the predictive power of historical height loss in clinical vertebral fracture assessment

After introducing radiation-free spinometry as a diagnostic tool to predict prevalent vertebral fractures, its validity and comparison with established tools such as historical height loss (HHL) was missing. This study shows that radiation-free spinometry is valid and its application adds predictive power to the ability of HHL to assess presence of vertebral fractures.

INTRODUCTION

Recently, radiation-free spinometry was introduced to identify patients with vertebral fractures (VFs). The goals of this study were to validate previous findings and to test the predictive accuracy of radiation-free spinometry compared to the assessment of historical height loss (HHL).

METHODS

We analyzed 304 patients [258 (85%) females (age range, 42-90 years) and 46 males (50-84 years)], including 108 patients with VFs. We performed receiver operator characteristic and net reclassification improvement (NRI) analyses to quantify the predictive power and the added predictive ability of radiation-free spinometry and HHL for VFs.

RESULTS

The estimated odds ratios in the thoracic and the lumbar spine showed no significant differences compared to the previously published, except for the effect of thoracic kyphosis in region "Th12 + L4-5." Radiation-free spinometry and HHL were both moderately accurate to raise suspicion for VFs. According to the NRI, which is defined as the net sum of the predicted risk increase in individuals who have VFs and the predicted net risk decrease for those who have not, we found significant improvements in all regions of interest when HHL and radiation-free spinometry were used in combination (area under the curve (AUC) 0.729-0.788).

CONCLUSION

Our results based on a new data set suggest validity of the prognostic score published previously. In addition, although our findings did not confirm our initial hypothesis that radiation-free spinometry alone performs superior to the assessment of HHL to predict VFs, we showed that radiation-free spinometry still adds predictive power to the ability of HHL to discriminate patients with VFs.

Automatic camera-based identification and 3-D reconstruction of electrode positions in electrocardiographic imaging

Electrocardiographic imaging (ECG imaging) is a method to depict electrophysiological processes in the heart. It is an emerging technology with the potential of making the therapy of cardiac arrhythmia less invasive, less expensive, and more precise. A major challenge for integrating the method into clinical workflow is the seamless and correct identification and localization of electrodes on the thorax and their assignment to recorded channels. This work proposes a camera-based system, which can localize all electrode positions at once and to an accuracy of approximately 1 ± 1 mm. A system for automatic identification of individual electrodes is implemented that overcomes the need of manual annotation. For this purpose, a system of markers is suggested, which facilitates a precise localization to subpixel accuracy and robust identification using an error-correcting code. The accuracy of the presented system in identifying and localizing electrodes is validated in a phantom study. Its overall capability is demonstrated in a clinical scenario.

Development of a morphing technique for predicting the position and size of an artificial ear in hemifacial microsomia patients

PURPOSE

People with hemifacial microsomia may be missing an ear on the affected side of the face. The principal aim of the study was to develop a morphing technique and to determine whether it could be used to appropriately position an artificial ear, as well as to give an indication of prosthesis size in comparison with the natural ear. Comparisons also were made between the artificial ears being worn by the patients with their natural ears.

MATERIALS AND METHODS

Data from stereophotogrammetry images of the faces of 10 people were converted into stereolithographic format. Anthropometric points on the face and ear of the unaffected side were plotted. By a process of scaling, the distance between facial landmarks on the unaffected side was estimated for the affected side so as to identify where the morphed ear would be positioned once generated.

RESULTS

Generally, the morphed ears appeared to be in acceptable positions. There was a statistically significant difference between the position of the morphed and natural ears (P = .011), as well as the artificial and natural ears (P = .001), but this was unlikely to have any clinical implications. There were no significant differences among the sizes of the natural, morphed, and artificial ears (P = .072).

CONCLUSIONS

Morphing appears to offer a more precise way of planning the positioning and construction of an artificial ear on patients with hemifacial microsomia than traditional methods. Differences in facial shape on either side of the face may impact on the process. This requires further study.

Efficient hybrid tree-based stereo matching with applications to postcapture image refocusing

Estimating dense correspondence or depth information from a pair of stereoscopic images is a fundamental problem in computer vision, which finds a range of important applications. Despite intensive past research efforts in this topic, it still remains challenging to recover the depth information both reliably and efficiently, especially when the input images contain weakly textured regions or are captured under uncontrolled, real-life conditions. Striking a desired balance between computational efficiency and estimation quality, a hybrid minimum spanning tree-based stereo matching method is proposed in this paper. Our method performs efficient nonlocal cost aggregation at pixel-level and region-level, and then adaptively fuses the resulting costs together to leverage their respective strength in handling large textureless regions and fine depth discontinuities. Experiments on the standard Middlebury stereo benchmark show that the proposed stereo method outperforms all prior local and nonlocal aggregation-based methods, achieving particularly noticeable improvements for low texture regions. To further demonstrate the effectiveness of the proposed stereo method, also motivated by the increasing desire to generate expressive depth-induced photo effects, this paper is tasked next to address the emerging application of interactive depth-of-field rendering given a real-world stereo image pair. To this end, we propose an accurate thin-lens model for synthetic depth-of-field rendering, which considers the user-stroke placement and camera-specific parameters and performs the pixel-adapted Gaussian blurring in a principled way. Taking ~1.5 s to process a pair of 640×360 images in the off-line step, our system named Scribble2focus allows users to interactively select in-focus regions by simple strokes using the touch screen and returns the synthetically refocused images instantly to the user.

Applicability of single-camera photogrammetry to determine body dimensions of pinnipeds: Galapagos sea lions as an example

Morphological features correlate with many life history traits and are therefore of high interest to behavioral and evolutionary biologists. Photogrammetry provides a useful tool to collect morphological data from species for which measurements are otherwise difficult to obtain. This method reduces disturbance and avoids capture stress. Using the Galapagos sea lion (Zalophus wollebaeki) as a model system, we tested the applicability of single-camera photogrammetry in combination with laser distance measurement to estimate morphological traits which may vary with an animal's body position. We assessed whether linear morphological traits estimated by photogrammetry can be used to estimate body length and mass. We show that accurate estimates of body length (males: ±2.0%, females: ±2.6%) and reliable estimates of body mass are possible (males: ±6.8%, females: 14.5%). Furthermore, we developed correction factors that allow the use of animal photos that diverge somewhat from a flat-out position. The product of estimated body length and girth produced sufficiently reliable estimates of mass to categorize individuals into 10 kg-classes of body mass. Data of individuals repeatedly photographed within one season suggested relatively low measurement errors (body length: 2.9%, body mass: 8.1%). In order to develop accurate sex- and age-specific correction factors, a sufficient number of individuals from both sexes and from all desired age classes have to be captured for baseline measurements. Given proper validation, this method provides an excellent opportunity to collect morphological data for large numbers of individuals with minimal disturbance.

Saliency detection for stereoscopic images

Many saliency detection models for 2D images have been proposed for various multimedia processing applications during the past decades. Currently, the emerging applications of stereoscopic display require new saliency detection models for salient region extraction. Different from saliency detection for 2D images, the depth feature has to be taken into account in saliency detection for stereoscopic images. In this paper, we propose a novel stereoscopic saliency detection framework based on the feature contrast of color, luminance, texture, and depth. Four types of features, namely color, luminance, texture, and depth, are extracted from discrete cosine transform coefficients for feature contrast calculation. A Gaussian model of the spatial distance between image patches is adopted for consideration of local and global contrast calculation. Then, a new fusion method is designed to combine the feature maps to obtain the final saliency map for stereoscopic images. In addition, we adopt the center bias factor and human visual acuity, the important characteristics of the human visual system, to enhance the final saliency map for stereoscopic images. Experimental results on eye tracking databases show the superior performance of the proposed model over other existing methods.

Discriminability limits in spatio-temporal stereo block matching

Disparity estimation is a fundamental task in stereo imaging and is a well-studied problem. Recently, methods have been adapted to the video domain where motion is used as a matching criterion to help disambiguate spatially similar candidates. In this paper, we analyze the validity of the underlying assumptions of spatio-temporal disparity estimation, and determine the extent to which motion aids the matching process. By analyzing the error signal for spatio-temporal block matching under the sum of squared differences criterion and treating motion as a stochastic process, we determine the probability of a false match as a function of image features, motion distribution, image noise, and number of frames in the spatio-temporal patch. This performance quantification provides insight into when spatio-temporal matching is most beneficial in terms of the scene and motion, and can be used as a guide to select parameters for stereo matching algorithms. We validate our results through simulation and experiments on stereo video.

Historical photogrammetry: Bird's Paluxy River dinosaur chase sequence digitally reconstructed as it was prior to excavation 70 years ago

It is inevitable that some important specimens will become lost or damaged over time, conservation is therefore of vital importance. The Paluxy River dinosaur tracksite is among the most famous in the world. In 1940, Roland T. Bird described and excavated a portion of the site containing associated theropod and sauropod trackways. This excavated trackway was split up and housed in different institutions, and during the process a portion was lost or destroyed. We applied photogrammetric techniques to photographs taken by Bird over 70 years ago, before the trackway was removed, to digitally reconstruct the site as it was prior to excavation. The 3D digital model offers the opportunity to corroborate maps drawn by R.T. Bird when the tracksite was first described. More broadly, this work demonstrates the exciting potential for digitally recreating palaeontological, geological, or archaeological specimens that have been lost to science, but for which photographic documentation exists.

Cascaded Kalman and particle filters for photogrammetry based gyroscope drift and robot attitude estimation

Based on a cascaded Kalman-Particle Filtering, gyroscope drift and robot attitude estimation method is proposed in this paper. Due to noisy and erroneous measurements of MEMS gyroscope, it is combined with Photogrammetry based vision navigation scenario. Quaternions kinematics and robot angular velocity dynamics with augmented drift dynamics of gyroscope are employed as system state space model. Nonlinear attitude kinematics, drift and robot angular movement dynamics each in 3 dimensions result in a nonlinear high dimensional system. To reduce the complexity, we propose a decomposition of system to cascaded subsystems and then design separate cascaded observers. This design leads to an easier tuning and more precise debugging from the perspective of programming and such a setting is well suited for a cooperative modular system with noticeably reduced computation time. Kalman Filtering (KF) is employed for the linear and Gaussian subsystem consisting of angular velocity and drift dynamics together with gyroscope measurement. The estimated angular velocity is utilized as input of the second Particle Filtering (PF) based observer in two scenarios of stochastic and deterministic inputs. Simulation results are provided to show the efficiency of the proposed method. Moreover, the experimental results based on data from a 3D MEMS IMU and a 3D camera system are used to demonstrate the efficiency of the method.

Application of a photogrammetric kinematic model for prediction of lung volumes in adolescents: a pilot study

BACKGROUND

There are several ways to measure the respiratory system, among them inductance plethysmography and three-dimensional kinematic analysis, methods of high cost and difficult transportability. The objective of this study was to correlate respiratory volumes obtained by spirometry standard equipment with a biomechanical model photogrammetric analysis of adolescents.

METHODS

We evaluated 50 subjects of both genders, aged between 14 and 17 years old, excluding those with respiratory obstruction or restriction. Stickers with markers, there was a five-point mapping for anatomical modeling and photogrammetry, with each evaluated in supine position, was sought to test the Forced Vital Capacity (FVC). The test was filmed and repeated three times. Images of the films were extracted for the moment of maximum exhalation and inhalation of proof with better breathing. With the use of a commercial software, defined the respiratory volumes to the thorax and abdomen.

RESULTS

The photogrammetric analysis has found values strongly correlated with the spirometric measurements of FVC (0.812), forced expiratory volume in one second (FEV1 - 0.708), Peak Expiratory Flow (PEF - 0.762) in addition to post test performed Inspiration (IP- 0.816). There was a higher ventilatory mobility for boys than girls for Lower Chest and Lower and Upper Abdomen. It was possible to reach a regression R2 = 0.866 for proof of FVC and R2 = 0.776 for IP with the use of photogrammetry, presenting a standard error of 0.353 and 0.451, respectively.

CONCLUSIONS

Photogrammetry can be used to study thoracoabdominal movements by applying analytical two-dimensional and three-dimensional images acquired using a video camera being, applicable and reproducible.

A new 4-dimensional imaging system for jaw tracking

A non-invasive 4D imaging system that produces high resolution time-based 3D surface data has been developed to capture jaw motion. Fluorescent microspheres are brushed onto both tooth and soft-tissue areas of the upper and lower arches to be imaged. An extraoral hand-held imaging device, operated about 12 cm from the mouth, captures a time-based set of perspective image triplets of the patch areas. Each triplet, containing both upper and lower arch data, is converted to a high-resolution 3D point mesh using photogrammetry, providing the instantaneous relative jaw position. Eight 3D positions per second are captured. Using one of the 3D frames as a reference, a 4D model can be constructed to describe the incremental free body motion of the mandible. The surface data produced by this system can be registered to conventional 3D models of the dentition, allowing them to be animated. Applications include integration into prosthetic CAD and CBCT data.

Variational stereo imaging of oceanic waves with statistical constraints

An image processing observational technique for the stereoscopic reconstruction of the waveform of oceanic sea states is developed. The technique incorporates the enforcement of any given statistical wave law modeling the quasi-Gaussianity of oceanic waves observed in nature. The problem is posed in a variational optimization framework, where the desired waveform is obtained as the minimizer of a cost functional that combines image observations, smoothness priors and a weak statistical constraint. The minimizer is obtained by combining gradient descent and multigrid methods on the necessary optimality equations of the cost functional. Robust photometric error criteria and a spatial intensity compensation model are also developed to improve the performance of the presented image matching strategy. The weak statistical constraint is thoroughly evaluated in combination with other elements presented to reconstruct and enforce constraints on experimental stereo data, demonstrating the improvement in the estimation of the observed ocean surface.

The evidence supporting methods of tooth width measurement: Part I. Vernier calipers to stereophotogrammetry

Measuring tooth widths is a key component of orthodontic treatment planning. Over recent decades, many methods have been proposed to achieve this purpose. The current review highlights and describes the initial techniques. The evidence behind their use is presented along with a brief discussion of their benefits and shortfalls. With knowledge and understanding of the accuracy and limitations of the various measurement methods, the clinician may be better informed and therefore able to select the most appropriate method for clinical practice.

Comparison of parameters of spinal curves in the sagittal plane measured by photogrammetry and inclinometry

BACKGROUND. The photogrammetric method and inclinometer-based measurements are commonly employed to assess the anteroposterior curvatures of the spine. These methods are used both in clinical trials and for screening purposes. The aim of the study was to compare the parameters used to characterise the anteroposterior spinal curvatures as measured by photogrammetry and inclinometry. MATERIAL AND METHODS. The study enrolled 341 subjects: 169 girls and 172 boys, aged 4 to 9 years, from kindergartens and primary schools in Rzeszów. The anteroposterior spinal curvatures were examined by photogrammetry and with a mechanical inclinometer. RESULTS. There were significant differences in the α angle between the inclinometric and photogrammetric assessment in the Student t test (p=0.017) and the Fisher Snedecor test (p=0.0001), with similar differences in the β angle (Student's t p=0.0001, Fisher Snedecor p=0.007). For the γ angle, significant differences were revealed with Student's t test (p=0.0001), but not with the Fisher Snedecor test (p = 0.22). CONCLUSIONS. 1. Measurements of inclination of particular segments of the spine obtained with the photogrammetric method and the inclinometric method in the same study group revealed statistically significant differences. 2. The results of measurements obtained by photogrammetry and inclinometry are not comparable. 3. Further research on agreement between measurements of the anteroposterior spinal curvatures obtained using the available measurement equipment is recommended.

A 3D anthropometric analysis of the orolabial region in Chinese young adults

The orolabial region undergoes considerable changes after orthognathic surgery or orthodontic treatment. Ethnicity, age, and sex-specific norms are needed during the planning of interventions in this region. In 2008 the Br J Oral Maxillofac Surg published anthropometric measurements of the lips of Chinese children, but to our knowledge such reference data for young Chinese adults are not currently available. We therefore used digital anthropometry on 3-dimensional craniofacial images acquired from 103 healthy young Chinese adults with Class I skeletal pattern. Anthropometric landmarks were identified, which provided linear and angular measurements. All orolabial measurements were significantly larger in men than women, with the exception of the labiomental angle. In contrast, there were no sex differences in the anthropometric proportions. We therefore provide what we think are the first cross-sectional norms available for young Chinese adults. These norms can be used to evaluate the morphology of the lips objectively for preoperative diagnosis, planning of treatment, and assessment of postoperative outcomes.

The role of the golden proportion in the evaluation of facial esthetics

OBJECTIVE

To demonstrate if one or more golden relationships between different measurements of the human face exist.

MATERIALS AND METHODS

To make our measurements, we used three-dimensional (3D) stereophotogrammetry, which has proved to be the "gold standard" in the field of facial anthropometry. We obtained 3D stereophotogrammetric facial acquisitions of 400 healthy young adult subjects, then had them scored by an Evaluation Jury. Each subject received an esthetic evaluation ranging from 0 to 40. Individuals with a score larger than 28 were considered very attractive (VA), and individuals with a score lower than 12 were considered not attractive (NA). Fifteen subjects per group were chosen by chance, with a final total group of 60 subjects: 15 VA males, 15 NA males, 15 VA females, and 15 NA females. For each subject, a set of facial distances was obtained from the stereophotogrammetric facial reconstruction, and 10 ratios were computed. The effects of sex and attractiveness were tested by analysis of variance. Additionally, Student's t-tests verified if the ratios were statistically different from the golden ratio.

RESULTS

For nine ratios, no significant effects of sex or attractiveness were found. Only the eye-mouth distance/height of the mandible ratio was significantly influenced by sex (P = .035) and attractiveness (P = .032). Seven out of 10 ratios were statistically different from the hypothetical value of 1.618, and only three of them were similar to the golden ratio.

CONCLUSIONS

Ratios between 3D facial distances were not related to attractiveness. Most of the facial ratios were different from the golden ratio.

Evaluation of a novel spine and surface topography system for dynamic spinal curvature analysis during gait

Introduction

The assessment of spinal deformities with rasterstereography can enhance the understanding, as well as can reduce the number of x-rays needed. However, to date this technique only allows measurements under static conditions. Since it would be of great value to be able to also analyze the spine in dynamic conditions, the present study evaluated a novel rasterstereographic system.

Materials and Methods

A new rasterstereographic device was evaluated in a comparison with the gold standard in motion analysis, the VICON system. After initial testing using 12 flat infrared markers adhered to a solid plate, the two systems were evaluated with the markers adhered onto the backs of 8 test subjects. Four triangles were defined using the markers, and the sides of each triangle were measured under static and dynamic conditions.

Results

On the solid plate, the sides of the 4 triangles were measured with a measuring tape and then by the two optical systems. Rasterstereography showed a high accuracy in marker detection on the solid plate. Under dynamic conditions, with the subjects walking on a treadmill, the rasterstereographically-measured side lengths were compared with the lengths measured by the VICON system as an assessment of marker detection. No significant differences (p>0.05) were found between the systems, differing only 0.07–1.1% for all sides of the four triangles with both systems.

Discussion

A novel rasterstereographic measurement device that allows surface and spine topography under dynamic conditions was assessed. The accuracy of this system was with one millimeter on a solid plate and during dynamic measurements, to the gold standard for motion detection. The advantage of rasterstereography is that it can be used to determine a three-dimensional surface map and also allows the analysis of the underlying spine.

Influence of non-traumatic thoracic and lumbar vertebral fractures on sagittal spine alignment assessed by radiation-free spinometry

Due to missing indications for specific diagnostics, the majority of non-symptomatic vertebral fractures are not diagnosed. This study shows the ability of radiation-free spinometry to assess sagittal spine parameters to raise suspicion for new non-traumatic thoracic and lumbar vertebral fractures and indicate specific diagnostics.

INTRODUCTION

The primary aim of this study was to investigate the accuracy of radiation-free spinometry to predict new non-traumatic vertebral fractures (VF) by the assessment of thoracic kyphosis (TK), lumbar lordosis (LL), and trunk inclination.

METHODS

Three hundred sixty-one patients (278 females and 83 males; age, 67.0 ± 8.6 years) were enrolled. In 86 women and 24 men, at least one non-traumatic VF was confirmed by radiography, MRI, and/or CT. Spinometry (video rasterstereography) was used to assess TK, LL, and trunk inclination. Receiver operating characteristic (ROC) and multivariate logistic regression analyses were performed to test the influence of age, sex, number, location, and grade of fractures on sagittal spine alignment.

RESULTS

TK, LL, and trunk inclination were associated with advancing age (p < 0.05). Patients with prevalent thoracic and lumbar VFs showed increased TK (p < 0.001), decreased LL (p < 0.001), and increased trunk inclination (p < 0.001) in comparison to patients without VFs. ROC analysis revealed that the combination of TK and LL presented with the best predictive accuracy to raise suspicion for new grade 2 or grade 3 VFs in the thoracic and the lumbar spine (AUC, 0.752-0.771). Odds ratio (OR) showed an increased risk for VFs with increased TK (OR, 1.05-1.11; p < 0.001) and LL (1.05-1.07; p < 0.001) in specified regions of interest. A TK <50° (sensitivity, 88-100 %; specificity, 23-25 %) and LL (78-92 %; 24-27 %) were considered as appropriate cutoffs for future screening.

CONCLUSION

Spinometry showed better predictive accuracy than historical height loss. Severe changes of TK and LL may help to raise suspicion of new VFs radiation-free and indicate proper diagnostics, such as radiographs, MRI, or CT.

Reproducibility of facial soft tissue landmarks on facial images captured on a 3D camera

OBJECTIVE

Fast and non-invasive systems of the three-dimensional (3D) technology are a recent trend in orthodontics. The reproducibility of facial landmarks is important so that 3D facial measurements are accurate and may-be applied clinically. The aim of this study is to evaluate the reproducibility of facial soft tissue landmarks using a non-invasive stereo-photogrammetry 3D camera.

MATERIAL AND METHODS

Twenty-four soft tissue landmarks on 3D facial images captured using a VECTRA-3D dual module camera system for full face imaging (Canfield Scientific inc, Fairfield, NJ, USA) were viewed and analysed using Mirror software on 30 adult subjects (15 males and 15 females, in the age range of 20-25 years). The landmarks were identified, recorded and measured twice on each 3D facial image by one examiner after a 2-week interval. Intra-class correlations and paired t-test or Wilcoxon Rank test were performed for each landmark to assess intra-examiner reproducibility.

RESULTS

Intra-class correlation coefficients for all 24 landmarks ranged from 0.68 to 0.97, indicating moderate to high reliability and reproducibility of all facial soft tissue landmarks. Paired t-tests and Wilcoxon Rank test also revealed that there were no significant differences in all 24 facial soft tissue landmarks measurements (p = 0. 17 - 0.99).

CONCLUSION

The results indicated that the reproducibility of identification of landmarks by one operator on facial images captured using a VECTRA-3D camera was acceptable. This device may be useful in treatment planning and may provide accurate information in making clinical decisions. However, it is suggested that further studies on inter-examiner reproducibility should be undertaken.

Preserving the impossible: conservation of soft-sediment hominin footprint sites and strategies for three-dimensional digital data capture

Human footprints provide some of the most publically emotive and tangible evidence of our ancestors. To the scientific community they provide evidence of stature, presence, behaviour and in the case of early hominins potential evidence with respect to the evolution of gait. While rare in the geological record the number of footprint sites has increased in recent years along with the analytical tools available for their study. Many of these sites are at risk from rapid erosion, including the Ileret footprints in northern Kenya which are second only in age to those at Laetoli (Tanzania). Unlithified, soft-sediment footprint sites such these pose a significant geoconservation challenge. In the first part of this paper conservation and preservation options are explored leading to the conclusion that to ‘record and digitally rescue’ provides the only viable approach. Key to such strategies is the increasing availability of three-dimensional data capture either via optical laser scanning and/or digital photogrammetry. Within the discipline there is a developing schism between those that favour one approach over the other and a requirement from geoconservationists and the scientific community for some form of objective appraisal of these alternatives is necessary. Consequently in the second part of this paper we evaluate these alternative approaches and the role they can play in a ‘record and digitally rescue’ conservation strategy. Using modern footprint data, digital models created via optical laser scanning are compared to those generated by state-of-the-art photogrammetry. Both methods give comparable although subtly different results. This data is evaluated alongside a review of field deployment issues to provide guidance to the community with respect to the factors which need to be considered in digital conservation of human/hominin footprints.

Calibration of a trinocular system formed with wide angle lens cameras

To obtain 3D information of large areas, wide angle lens cameras are used to reduce the number of cameras as much as possible. However, since images are high distorted, errors in point correspondences increase and 3D information could be erroneous. To increase the number of data from images and to improve the 3D information, trinocular sensors are used. In this paper a calibration method for a trinocular sensor formed with wide angle lens cameras is proposed. First pixels locations in the images are corrected using a set of constraints which define the image formation in a trinocular system. When pixels location are corrected, lens distortion and trifocal tensor is computed.

Computerized photogrammetry used to calculate the brow position index

BACKGROUND

The orbital region is of vital importance to facial expression. Brow ptosis, besides having an impact on facial harmony, is a sign of aging. Various surgical techniques have been developed to increase the efficacy of brow-lift surgery. However, no consensus method exists for an objective measurement of the eyebrow position due to the curvature of the face. Therefore, this study aimed to establish a method for measuring the eyebrow position using computerized photogrammetry.

METHODS

For this study, 20 orbital regions of 10 volunteers were measured by direct anthropometry using a digital caliper and by indirect anthropometry (computerized photogrammetry) using standardized digital photographs. Lines, points, and distances were defined based on the position of the anthropometric landmarks endocanthion and exocanthion and then used to calculate the brow position index (BPI). Statistical analysis was performed using Student's t test with a significance level of 5 %.

RESULTS

The BPI values obtained by computerized photogrammetric measurements did not differ significantly from those obtained by direct anthropometric measurements (p > 0.05). The mean BPI was 84.89 ± 10.30 for the computerized photogrammetric measurements and 85.27 ± 10.67 for the direct anthropometric measurements.

CONCLUSION

The BPI defined in this study and obtained by computerized photogrammetry is a reproducible and efficient method for measuring the eyebrow position.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article.