Ahmad Jawad Nasri - Academia.edu (original) (raw)

Papers by Ahmad Jawad Nasri

2009 IEEE International Symposium on Signal Processing and Information Technology (ISSPIT), 2009

The quality of image interpretation depends strongly on the segmentation process which is an impo... more The quality of image interpretation depends strongly on the segmentation process which is an important step in image processing. Most of the segmentation methods and approaches are not suitable for noisy environments such as satellite images of high resolution. Sometime they require a priori knowledge, and another time they do not work on all types of images. Self-organizing maps (SOMs)

International Journal of Remote Sensing, 2009

Image segmentation is an essential process in image analysis. Several methods have been developed... more Image segmentation is an essential process in image analysis. Several methods have been developed to segment multicomponent images and the success of these methods depends on the characteristics of the acquired image and the percentage of imperfections in the process of its acquisition. Many of the segmentation methods are parametric, which means that many parameters need to be computed or provided before the segmentation process, and any method that works on one type of multicomponent image cannot necessarily work on another. In addition, many segmentation methods are supervised, where a priori knowledge is needed, such as the number of classes. To overcome these obstacles, a self-organizing map (SOM), which is an unsupervised nonparametric method, was used to segment four different types of multicomponent images (Landsat, SPOT, IKONOS and CASI), and the results compared to those of a new nonparametric unsupervised genetic algorithm (GA) for image segmentation. To improve the performance of the GA, a hill-climbing process and another random heuristic module were added to escape the local-minima trap and to improve the speed of the GA; the new algorithm is called the hybrid genetic algorithm (HGA). Verification of the results was performed using two different techniques: field verification and the functional model. These verification techniques show that the HGA is more accurate in multicomponent image segmentation than the SOM.

Computer-Aided Design, 2013

Garment creation continues to be the most tedious part of the virtual clothing process. In this p... more Garment creation continues to be the most tedious part of the virtual clothing process. In this paper, we present an easy to use sketch-based cloth modeling approach. Contours can be easily sketched on a mannequin to generate quad meshes to represent pieces of cloth already fit and draped. Typically, the clothing process depends highly on the meshing scheme that has to infer its geometry from the input boundary. Our quad meshing scheme is based on discrete Coons patches but with arbitrary boundary input. We also apply the permanence principle to our topological solution to allow more control over the influence of the input boundary polyline on the interior output polygonal mesh. This facilitates the creation of folds that are strongest in curvature at the boundary and which diminish towards the interior. The generated garments can then be easily animated in a simulation system based on Finite Elements, using a rediscretization of the generated mesh and a reconstructed metric of the cloth surface.

Through its grants, the National Science Foundation sponsors workshops that inform faculty of cur... more Through its grants, the National Science Foundation sponsors workshops that inform faculty of current topics in computer science. Such a workshop, entitled, "Developing Multimedia-based Interactive Laboratory Modules for Computer Science," was given July 27-August 6, 1998, at Illinois State University at Normal. Each participant was expected to design and implement a small part of a laboratory module. This paper describes what five .of the faculty members who participated have done with the knowledge obtained from the workshop. (Contains 22 references.) (Author/MES) Reproductions supplied by EDRS are the best that can be made from the original document.

The Visual Computer, 2003

A recursive-subdivision surface interpolating a mesh of curves can be generated from a given poly... more A recursive-subdivision surface interpolating a mesh of curves can be generated from a given polygonal mesh (or a polyhedron) and some tagged control polygons by constructing a polygonal complex for each of these polygons. This process will modify the geometry, and possibly the topology, of the polygonal mesh and could result in poorly shaped surfaces across the interpolated curves. The problem can be minimized by applying some fairing procedure that regularly repositions the vertices of the mesh. This paper provides an approach to regularize a polygonal mesh based on the Laplacian and mean curvature of the vertices. The results are useful, especially if further constraints such as normal or cross curvature are imposed across the interpolated curves, where more irregularity can be introduced on the polygonal mesh.

Computer-Aided Design and Applications, 2004

The problem of constructing a smooth subdivision surface interpolating multiple intersecting curv... more The problem of constructing a smooth subdivision surface interpolating multiple intersecting curves was partially addressed in the literature. In the context of Doo-Sabin subdivision surfaces, Nasri[3] presented a solution to interpolate unlimited number of curves through an extraordinary point. In the Catmull-Clark setting, no more than two intersecting curves could so far be interpolated. That is, the interpolation of multiple intersecting curves remains a non-trivial and elusive problem. This paper puts forth a solution to this problem. The solution relies in a fundamental way on the by-now well-known notion of Catmull-Clark Polygonal Complexes introduced in [5].

Geometric Modeling and Processing - GMP 2006, 2006

A well-documented problem of Catmull and Clark subdivision is that, in the neighborhood of extrao... more A well-documented problem of Catmull and Clark subdivision is that, in the neighborhood of extraordinary point, the curvature is unbounded and fluctuates. In fact, since one of the eigenvalues that determines elliptic shape is too small, the limit surface can have a saddle point when the designer's input mesh suggests a convex shape. Here, we replace, near the extraordinary point, Catmull-Clark subdivision by another set of rules derived by refining each bi-cubic Bspline into nine. This provides many localized degrees of freedom for special rules so that we need not reach out to, possibly irregular, neighbor vertices when trying to improve, or tune the behavior. We illustrate a strategy how to sensibly set such degrees of freedom and exhibit tuned ternary quad subdivision that yields surfaces with bounded curvature, nonnegative weights and full contribution of elliptic and hyperbolic shape components.

2008 5th International Multi-Conference on Systems, Signals and Devices, 2008

... The second image is SPOT XS V pan sharpened (bands 1, 2, and 3 merge with the panchromatic ba... more ... The second image is SPOT XS V pan sharpened (bands 1, 2, and 3 merge with the panchromatic band) with 5 meter resolution and the size ofthe image is 540X 540 (see Figure 4b). ... The second experiment is conducted on SPOT V image. ...

Proceedings of the 6th Eurographics Symposium on Sketch-Based Interfaces and Modeling - SBIM '09, 2009

Designing a control mesh (or a polyhedron) for a subdivision model is a tedious task. It involves... more Designing a control mesh (or a polyhedron) for a subdivision model is a tedious task. It involves many difficult decisions such as how to minimize the number of extraordinary vertices, how best to choose their valencies, and where to place them in the control mesh. In this paper, we present an intuitive and interactive approach for using sketch-based interface to design subdivision models. The input to the system is a set of strokes forming the profile curves of the surface. From the constructed control polygons of the sketched curves, a coarse and quad dominant control mesh is generated with few extraordinary vertices or faces. The corresponding limit surface interpolates the profile curves with the capability of local control across these curves and of the model in general. Although our approach is oriented towards quad-based systems such as Catmull-Clark, it could well be adopted in other subdivision schemes.

Proceedings of the International Symposium on Computational Aesthetics in Graphics, Visualization, and Imaging - CAe '11, 2011

Muqarnas is a mesmerizing 3D feature of Islamic architecture that exhibit intricate geometry. Suc... more Muqarnas is a mesmerizing 3D feature of Islamic architecture that exhibit intricate geometry. Such designs are composed of several basic structures combined in successive layers, producing complicated 3D surfaces. In this paper we propose a new approach for interactive modelling of muqarnas based on their layered structure. As a guidance for the modeling workflow, floor plans are used. We also discuss how to edit the resulting models and how to automatically generate new forms.

Sarfraz/Geometric Modeling, 2005

Geometric Modeling and Processing. Theory and Applications. GMP 2002. Proceedings

One essential interpolation constraint on subdivision surfaces is curve interpolation. Subdivisio... more One essential interpolation constraint on subdivision surfaces is curve interpolation. Subdivision surfaces through predefined meshes of curves can now be generated using either variations of existing subdivision schemes or (in our case) polygonal complexes. This paper goes one step further; given a sequence of cross sectional curves (ci), each defined by a uniform cubic B-spline control polygon (cpi), we present

Computer-Aided Design and Applications, 2006

Accurate reduction of two-dimensional curve noises is crucial to metrology and reverse engineerin... more Accurate reduction of two-dimensional curve noises is crucial to metrology and reverse engineering. In this paper we propose a set of schemes for two-dimensional curve denoising. Our approach consists of three main steps: 1) feature-based pre-smoothing of noised polylines; 2) curve partitioning of polylines into different regions; 3) two hybrid denoising schemes of arbitrary polylines with noises. Numerical experiments indicate the effectiveness of our approach against existing methods.

The Visual Computer, 2007

Sketch-based interfaces are becoming a useful methodology for interaction with a wide range of ap... more Sketch-based interfaces are becoming a useful methodology for interaction with a wide range of applications. Drawing is a natural and simple paradigm for designers. One of the problems in most of the current generation of such interfaces is that designers are forced to use single strokes where they may prefer to use many strokes while drawing with traditional tools such as a pencil. In this work we have addressed this problem by analyzing multiple strokes and replacing them with a single stroke that makes a reasonable estimate of the designer's intention. Our solution recursively subdivides space stopping where either there is only a single stroke, or several strokes that have a proper ordering using principal component analysis. The subspaces are then reconnected, and the orderings are joined to create the control points of a single B-spline curve. The resulting curve is very noisy due to the multitude of strokes. A multi-resolution technique that makes use of reverse subdivision has been used to fit a smooth B-spline curve.

The Visual Computer, 2002

This paper is the first of two, which together describe and classify the various situations that ... more This paper is the first of two, which together describe and classify the various situations that any complete study of interpolation constraints for a recursive subdivision surface needs to consider. They do so in the form of a systematic taxonomy of situations. Presented here are curve cases, which provide good illustrations of principles which will be used in both contexts; surfaces will be addressed in the second paper. Known results are classified and open questions identified.

The Visual Computer, 2010

This paper presents a constructive method for generating a uniform cubic B-spline curve interpola... more This paper presents a constructive method for generating a uniform cubic B-spline curve interpolating a set of data points simultaneously controlled by normal and curvature constraints. By comparison, currently published methods have addressed one or two of those constraints (point, normal or cross-curvature interpolation), but not all three constraints simultaneously with C2 continuity. Combining these constraints provides better control of the generated curve in particular for feature curves on free-form surfaces. Our approach is local and provides exact interpolation of these constraints.

IET Image Processing, 2009

Image segmentation is an important task in image analysis and processing. Many of the existing me... more Image segmentation is an important task in image analysis and processing. Many of the existing methods for segmenting a multi-component image (satellite or aerial) are very slow and require a priori knowledge of the image that could be difficult to obtain. Furthermore, the success of each of these methods depends on several factors, such as the characteristics of the acquired image, resolution limitations, intensity in-homogeneities and the percentage of imperfections induced by the process of image acquisition. Recently, fuzzy C-means (FCM) and Genetic Algorithms were separately used in segmenting multi-component images but neither of them had successfully addressed the above concerns. GA was enhanced using Hill-climbing, randomising, and modified mutation operators, leading to what is called hybrid dynamic genetic algorithm (HDGA). Coupling HDGA and FCM creates an unsupervised segmentation method which could successfully segment two types of multi-component images (Landsat ETMþ, and IKONOS II). Comparison with the four different methods FCM, hybrid genetic algorithm (HGA), self-organizing-maps (SOM), and the combination of SOM and HGA (SOM-HGA) reveals that FCM-HDGA segmentation method gives robust and reliable results, and is more time efficient.

IEEE Geoscience and Remote Sensing Letters, 2007

Image segmentation is an essential process for image analysis. Several methods were developed to ... more Image segmentation is an essential process for image analysis. Several methods were developed to segment multicomponent images, and the success of these methods depends on several factors including (1) the characteristics of the acquired image and (2) the percentage of imperfections in the process of image acquisition. The majority of these methods require a priori knowledge, which is difficult to

Computers & Graphics, 2002

Generating subdivision surfaces with curve interpolation constraints is needed in both computer g... more Generating subdivision surfaces with curve interpolation constraints is needed in both computer graphics and geometric modeling applications. In the context of the Doo-Sabin subdivision scheme, this can be achieved through the use of polygonal complexes as suggested by Nasri (Presented at the Fifth Siam Conference on Geometric Design, Nashville, 1997; Comput. Aided Geom. Des. 17 (2000) 595). A polygonal complex is simply a polygonal mesh whose structure depends on the subdivision scheme used and whose limit of subdivision is a curve rather than a surface. The subdivision scheme applied to these complexes is basically the same applied to the mesh defining the surface but with possible modification of its subdivision rules. The advantage of that lies in the retention of the same subdivision coefficients, thus saving the need for any further analysis at the limit. In this paper, we propose a method for using polygonal complexes to generate Catmull-Clark subdivision surfaces with curve interpolation constraints. The polygonal complexes are embedded here in the given mesh, which can possibly interpolate intersecting curves.

Computer Science Education, 1995

ABSTRACT Hypermedia systems are combinations of multimedia systems and hypertext. They have a gre... more ABSTRACT Hypermedia systems are combinations of multimedia systems and hypertext. They have a great potential in education and, in particular, in computer science education. This article describes a method to develop a hypermedia system for computer systems education. Such a system will be used in teaching an introductory course in computer systems. It provides an ideal interactive environment for learning, teaching, designing, and implementing students’ projects in computer organization and related topics. The article also reports on the progress of developing a prototype system for the computer science program at the American University of Beirut.