Amit Shesh

SMARTPAPER: An Interactive and User Friendly Sketching System

This paper describes an interactive sketching system for 3D design/modeling that diverts from the conventional menu‐and‐button interfaces of CAD tools. The system, dubbed SMARTPAPER, offers a unified sketching environment that supports direct sketching as well as gestured sketching with more emphasis on the former to encourage natural sketching styles. SMARTPAPER also provides a unified 2D and 3D drawing domain by allowing the user to sketch directly on a 3D model in addition to the usual 2D sketching from scratch. A natural sketching experience is offered by supporting casual sketching consisting of wiggly, discontinuous, overlapping strokes. The system is empowered by an array of seamlessly integrated 2D and 3D features such as 2D sketch cleaning, 3D reconstruction from 2D sketch, 3D transformations, sketching on 3D, and conventional 3D CSG operations like cutting and joining. The key to the success of SMARTPAPER is efficient and robust 3D reconstruction from a single freehand 2D sketch with minimal hints. We have employed and improved Lipsons optimization method, originally designed for offline reconstruction of engineering drawings, in our interactive system by leveraging additional clues obtained by interaction during sketching.

Efficient and Dynamic Simplification of Line Drawings

In this paper we present a pipeline for rendering dynamic 2D/3D line drawings efficiently. Our main goal is to create efficient static renditions and coherent animations of line drawings in a setting where lines can be added, deleted and arbitrarily transformed on‐the‐fly. Such a dynamic setting enables us to handle interactively sketched 2D line data, as well as arbitrarily transformed 3D line data in a unified manner. We evaluate the proximity of screen projected strokes to simplify them while preserving their continuity. We achieve this by using a special data structure that facilitates efficient proximity calculations in a dynamic setting. This on‐the‐fly proximity evaluation also facilitates generation of appropriate visibility cues to mitigate depth ambiguities and visual clutter for 3D line data. As we perform all these operations using only line data, we can create line drawings from 3D models without any surface information. We demonstrate the effectiveness and applicability of our approach by showing several examples with initial line representations obtained from a variety of sources: 2D and 3D hand‐drawn sketches and 3D salient geometry lines obtained from 3D surface representations.

Crayon lighting: sketch-guided illumination of models

An interactive and intuitive way of designing lighting around a model is desirable in many applications. In this paper, we present a tool for interactive inverse lighting in which a model is rendered based on sketched lighting effects. To specify target lighting, the user freely sketches bright and dark regions on the model as if coloring it with crayons. Using these hints and the geometry of the model, the system efficiently derives light positions, directions, intensities and spot angles, assuming a local point-light based illumination model. As the system also minimizes changes from the previous specifications, lighting can be designed incrementally. We formulate the inverse lighting problem as that of an optimization and solve it using a judicious mix of greedy and minimization methods. We also map expensive calculations of the optimization to graphics hardware to make the process fast and interactive. Our tool can be used to augment larger systems that use point-light based illumination models but lack intuitive interfaces for lighting design, and also in conjunction with applications like ray tracing where interactive lighting design is difficult to achieve.

Sketch-based Segmentation of Scanned Outdoor Environment Models

When modeling with scanned outdoor models, being able to select a subset of the points efficiently that collectively represent an object is an important and fundamental operation. Such segmentation problems have been extensively studied, and simple and efficient solutions exist in two dimensions. However, 3D segmentation, especially that of sparse point models obtained by scanning, remains a challenge because of inherent incompleteness and noise. We present a sketched-based interface that allows segmentation of general 3D point-based models. The user marks object and background regions by placing strokes using a stylus, and the tool segments out the marked object(s). To refine the results, the user simply moves the camera to a different location and repeats the process. Our method is based on graph cuts, a popular and well-tested paradigm for segmentation problems. We employ a two-pass process: we use the strokes to perform 2D image segmentation in the projection plane of the camera and use its results for the 3D scanned data segmentation. The advantages of our method are ease of use, speed and robustness. Our method works for general 3D point models and not just range images. Important applications include selection of objects when dealing with large, unorganized point models for refinement, remodeling, meshing, etc.

Toward a Singleton Undergraduate Computer Graphics Course in Small and Medium-sized Colleges

This article discusses the evolution of a single undergraduate computer graphics course over five semesters, driven by a primary question: if one could offer only one undergraduate course in graphics, what would it include? This constraint is relevant to many small and medium-sized colleges that lack resources, adequate expertise, and enrollment to sustain multiple courses in graphics that spread out its vast and evolving content. We strive to include material that would provide (1) a basic but solid theoretical foundation, (2) topics, data structures, and algorithms that are most practically used, (3) ample experience in actual graphics programming and (4) a basic awareness of advanced topics. We have a secondary objective of relating and complementing computer graphics knowledge and programming with topics in other computer science courses to provide a more cohesive understanding to our students. We achieve both objectives by using an “early-scenegraphs” approach to progressively create graphics applications that use XML-based modeling and both pipeline-based and ray traced rendering. We report and analyze results that show how students were able to achieve more complex results within similar time periods while largely retaining prior average student performance in the course. Students also report higher rates of satisfaction with the course when it follows our proposed approach. Pedagogically our main contribution is an evolving blueprint for a single undergraduate CG course that offers flexibility to emphasize different aspects like modeling, rendering, etc. according to the instructor’s and students’ interests, while aligning the course better within the computer science curriculum especially when resources are limited.

Peek-in-the-Pic: Flying Through Architectural Scenes From a Single Image*

Many casually taken ‘tourist’ photographs comprise of architectural objects like houses, buildings, etc. Reconstructing such 3D scenes captured in a single photograph is a very challenging problem. We propose a novel approach to reconstruct such architectural scenes with minimal and simple user interaction, with the goal of providing 3D navigational capability to an image rather than acquiring accurate geometric detail. Our system, Peek‐in‐the‐Pic, is based on a sketch‐based geometry reconstruction paradigm. Given an image, the user simply traces out objects from it. Our system regards these as perspective line drawings, automatically completes them and reconstructs geometry from them. We make basic assumptions about the structure of traced objects and provide simple gestures for placing additional constraints. We also provide a simple sketching tool to progressively complete parts of the reconstructed buildings that are not visible in the image and cannot be automatically completed. Finally, we fill holes created in the original image when reconstructed buildings are removed from it, by automatic texture synthesis. Users can spend more time using interactive texture synthesis for further refining the image. Thus, instead of looking at flat images, a user can fly through them after some simple processing. Minimal manual work, ease of use and interactivity are the salient features of our approach.

Scene Graph Creation And Management For Undergraduates

This paper describes the context and results of a student project related to scene graphs spanning several assignments in an undergraduate computer graphics course. The project progressively built an application that created a list of objects from an XML specification, modified it into a scene graph, implemented part-by-part animation and added point lights and textures. Students were encouraged to build creative models using implicit shapes. It was completed individually by 21 undergraduate students in three stages spanning 6− 7 weeks. This project was further extended in the last two assignments by incorporating a ray tracer within it.

GPU-generated "parameterized" trees

Incorporating different-looking trees in a single graphics application involves either loading numerous polygonal/point models, or generating them algorithmically. In any case, this increases the demand of rendering resources both in terms of computing power and memory to hold all models simultaneously. This paper presents a novel method that produces different-looking trees from a common domain starting from the same polygonal model. Since the shape of the canopy decides the appearance of large trees, we focus on generating canopies automatically from the same polygonal model and some parameters. Thus the generated canopies can be thought of as functions of a parameterized domain. A branch structure created separately then completes the tree model. Using this method, a program can maintain a single copy of the polygonal model, and create different tree models from it by merely changing these parameters. Our method can be efficiently implemented on a GPU, thereby allowing us to store only a few models directly in GPU memory and creating different-looking tree models from them at runtime.

Teaching Graphics To Students Struggling in Math: An Experience

Undergraduate students with a negative attitude towards Math present a unique challenge when teaching computer graphics. Most meaningful concepts in computer graphics involve directly working with Math in the classroom, and implementing tasks in programs requires a reasonable grounding in Math concepts and how to apply them. This paper presents a semester-long experience in using three strategies to address difficulties faced by computer science students who are interested in learning computer graphics, but feel less confident or uninterested in Math. Similar to how Math is taught in schools, we focus on giving students more and more practice in implementing progressively complex visual tasks. Students accomplish some tasks individually to develop a basic understanding before completing other tasks in groups. Students achieve more in a semester than before, and our preliminary observations show a higher rate of completion by students, moderate gains in performance in individual assignments and significant gains in overall class performance.