Paulo Cezar Pinto Carvalho

Computing geodesics on triangular meshes

We present a new algorithm to compute a geodesic path over a triangulated surface. Based on Sethians Fast Marching Method and Polthiers straightest geodesics theory, we are able to generate an iterative process to obtain a good discrete geodesic approximation. It can handle both convex and non-convex surfaces.

A Camera-Projector System for Real-Time 3D Video

In this paper, we describe a real-time 3D video system that is based on active stereo. Combining a NTSC standard camera/ projector equipment and a suitable color code, the geometric and photometric information of a scene is robustly obtained in 30fps. Our main motivation to develop this system is to create a platform for investigating the issues that will be posed by the next generation of digital video and how it can shape up new media.

Geodesic paths on triangular meshes

We present a new algorithm to compute a geodesic path over a triangulated surface. Based on Sethians (1996) fast marching method and Polthiers (1998) straightest geodesics theory, we are able to generate an iterative process to obtain a good discrete geodesic approximation. It can handle convex and nonconvex surfaces as well.

Analysis of spatial variability using geostatistical functions for diagnosis of lung nodule in computerized tomography images

This paper analyzes four geostatistical functions—semivariogram, semimadogram, covariogram, and correlogram—with the purpose of characterizing lung nodules as malignant or benign in computerized tomography images. The tests described in this paper were carried out using a sample of 30 nodules, 24 benign and 6 malignant. Stepwise discriminant analysis was used to determine which combination of measures were best able to discriminate between the benign and malignant nodules. Then, a linear discriminant analysis procedure was performed using the selected features to evaluate the ability of these features to predict the classification for each nodule. A leave-one-out procedure was used to provide a less biased estimate of the linear discriminator’s performance. All analyzed functions have value area under receiver operation characteristic (ROC) curve above 0.800, which means results with accuracy between good and excellent. The preliminary results of this approach are very promising in characterizing nodules using geostatistical functions.

Automatic Camera Calibration for Image Sequences of a Football Match

In the broadcast of sports events one can commonly see adds or logos that are not actually there - instead, they are inserted into the image, with the appropriate perspective representation, by means of specialized computer graphics hardware. Such techniques involve camera calibration and the tracking of objects in the scene. This article introduces an automatic camera calibration algorithm for a smooth sequence of images of a football (soccer) match taken in the penalty area near one of the goals. The algorithm takes special steps for the first scene in the sequence and then uses coherence to efficiently update camera parameters for the remaining images. The algorithm is capable of treating in real-time a sequence of images obtained from a TV broadcast, without requiring any specialized hardware.

Lloyd's Algorithm on GPU

The Centroidal Voronoi Diagram (CVD) is a very versatile structure, well studied in Computational Geometry. It is used as the basis for a number of applications. This paper presents a deterministic algorithm, entirely computed using graphics hardware resources, based on Lloyds Method for computing CVDs. While the computation of the ordinary Voronoi diagram on GPU is a well explored topic, its extension to CVDs presents some challenges that the present study intends to overcome.

Diagnosis of lung nodule using semivariogram and geometric measures in computerized tomography images.

This paper uses the geostatistical function - semivariogram and a set of 3D geometric measures - sphericity index, convexity index, extrinsic and intrinsic curvature index and surface type, to characterize lung nodules as malignant or benign in computerized tomography images. Based on a sample of 31 nodules, 25 benign and 6 malignant, these methods are first analyzed individually and then jointly, with techniques for classification and analysis (stepwise discriminant analysis, leave-one-out and ROC curve). We have concluded that the individual measures and their combinations produce good results in the diagnosis of lung nodules.

Image moments-based structuring and tracking of objects

This paper presents a new method for structuring and tracking of objects in video sequences. Our approach is based on image moments and the BSP-tree data structure. We use invariant properties of these moments to construct a BSP-tree and determine an ellipsis that approximates the objects shape. Then, we employ this information to track objects frame by frame through the image sequence. The method works well for segmented images with a single object and we assume that the motion will not change abruptly.

Diagnosis of lung nodule using Gini coefficient and skeletonization in computerized tomography images

This paper uses the Gini coefficient and a set of skeleton measures, with the purposes, with the purpose of characterizing lung nodules as malignant or benign in computerized tomography images.Based on a sample of 31 nodules, 25 benign and 6 malignant, these methods are first analyzed individually and then jointly, with classfication and analysis techniques (linear stepwise discriminant analysis, leave-one-out and ROC curve). We have concluded that the individual measures and their combinations produce good results in the diagnosis of lung nodules.

Motion reconstruction using moments analysis

This work presents a method for motion reconstruction. The approach is based on image moments and the bsp-tree data structure. We use invariant properties of these moments to construct a bsp-tree and determine a set of ellipses that approximates the objects shape in each frame. These ellipsoidal structures are matched, which allow us to track the object. Motion is represented by the geometric transformations between the sets of ellipses and stored in the hierarchical structure. Motion reconstruction is done by interpolating these transformations.