MARK-IT: A MARKING USER INTERFACE FOR CUTTING DECOMPOSITION TIME Nicholas C. Yang1 Andrew S. Forsberg1 Jason F. Shepherd2 Ricardo M. Garcia2 Karl G. Merkley3 1Brown University, Providence, RI, U.S.A. {nyang, asf}@cs.brown.edu 2Sandia National Laboratories, Albuquerque, NM, U.S.A. {jfsheph, ricgarc}@sandia.gov 3Elemental Technologies, Inc., American Fork, UT, U.S.A. [email protected] ABSTRACT We present Mark-It, a marking user interface that reduced the time to decompose a set of CAD models exhibiting a range of decomposition problems by as much as fifty percent. Instead of performing about 50 mesh decomposition operations using a conventional UI, Mark-It allows users to perform the same operations by drawing 2D marks in the context of the 3D model. The motivation for this study was to test the potential of a marking user interface for the decomposition aspect of the meshing process. To evaluate Mark-It, we designed a user study that consisted of a brief tutorial of both the non-marking and marking UIs, performing the steps to decompose four models contributed to us by experienced meshers at Sandia National Laboratories, and a post-study debriefing to rate the speed, preference, and overall learnability of the two interfaces. Our primary contributions are a practical user interface design for speeding-up mesh decomposition and an evaluation that helps characterize the pros and cons of the new user interface. Keywords: meshing, decomposition, marking user interface, gestural commands, time-to-mesh, post- WIMP 1. INTRODUCTION research are the current techniques for alleviating this bottleneck . This study focuses on the latter by testing The goal of meshing is to produce a discretization of whether the use of marking gestures, in the context of a space, a mesh, that is suitable for the simulation the 3D tasks at hand, can significantly reduce decom- of a given engineering problem. Meshing, particularly position time. As noted in [2], any type of automation hexahedral meshing, is a complicated procedure that or optimization in decomposition could “vastly reduce often requires the use of rather sophisticated, inter- the time to mesh for hexahedral elements.” active tools (i.e. CUBIT, TurboMesh, SolidMesh) to produce a usable mesh. For the user, decomposition Decomposition operations must be accessed through can be the most time-consuming part of the meshing a user interface in any meshing system. Two popu- process; it includes determining and specifying oper- lar UI styles are Windows-Icon-Menu-Pointer (WIMP) ations such as dividing and simplifying a model’s ge- and command-line. In general, user interfaces have re- ometry into more primitive pieces. Decomposition is mained mostly unchanged for the past two decades and usually required before an automatic meshing algo- predominantly consist of WIMP UIs [3]. Traditional rithm can be applied to components of a model. In WIMP UIs are widely popular mainly because they many cases, the decomposition as a whole cannot be have proven to be relatively easy-to-learn. Command- automatically performed and must be done manually; line UIs originated much longer ago but are sometimes oftentimes, the user is an irremovable part of the mesh- preferred for systems with large numbers of operators ing process [1]. Algorithmic and user interface (UI) and operands. Oftentimes, command-line UIs are sig- nificantly more efficient than WIMP UIs once mas- processing of the geometric model. In many cases, tered. especially cases with high problem complexity, a user must manually make decisions, using a tool such as In this study, we applied the concept of a post-WIMP CUBIT, to prepare a model for a given meshing al- UI to a sophisticated meshing system, Sandia National gorithm. These human-made decisions can improve Laboratories’ CUBIT, which has been in development overall efficiency in a way automatic algorithms can- for about 8 years and combines the best aspects of not. For example, the user may improve efficiency both conventional WIMP and command-line UIs. CU- by reducing the total number of elements created, im- BIT is a 2D and 3D finite element mesh generation proving the quality of elements created, or by mini- tool that produces meshes for finite element analysis. mizing the number of steps to achieve the required de- Development for the marking interface was done ex- composition. Nevertheless, this section goes into more clusively in CUBIT, but we expect the concepts of detail on non-user-based algorithmic approaches to re- the implemented marking UI to extend over to other duce the time-to-mesh and also discusses related work meshing systems as well. in marking post-WIMP UIs. Specifically, we developed a post-WIMP marking UI, which we have termed “Mark-It.” With Mark-It, users draw 2D lines in the context of 3D Computer-Aided 2.1 Algorithmic Approaches Design (CAD) models to specify meshing operations and operands. We hypothesized a marking UI would Historically, a great deal of effort has been spent in be effective due to the graphical nature of meshing reducing the time-to-mesh by introducing new mesh- tasks. The intent was to discover the advantages ing algorithms or improving the scope of existing al- and disadvantages of a specific marking UI targeted gorithms. Because of limitations in current hexahe- at mesh decomposition. Results from this study are dral meshing algorithms, algorithms for decomposing preliminary data that show how effective a marking models into mesh-able primitive shapes have received post-WIMP interface could be in a meshing context. a great deal of attention. Several examples of algo- Our results and evaluation suggest that for purposes rithmic work to reduce the time-to-mesh will be high- of meshing, our post-WIMP marking interface is faster lighted in this section. than most traditional WIMP interfaces. Furthermore, Two of the most highly used algorithms in hexahedral we also received feedback about several possible im- meshing today include the “mapping” and “sweep- provements to our marking UI that would make it ing” methods [4][5]. Enhancements to each of these faster and easier to learn. The advantages and dis- algorithms have been made specifically to reduce the advantages of both WIMP and post-WIMP interfaces amount of decomposition necessary to produce a mesh, are discussed in [3]. thereby speeding up the time to produce the mesh [6] The non-marking CUBIT interface we compared [1] [7]. Specifically, the “submapping” algorithm [1] Mark-It to consists of toolbars, menus, point-and-click and the many-to-many sweeping tools [8][9][10] [11] selection, and a command-line. Users in our study are the algorithms used heavily in CUBIT today. Both were asked to click on separate toolbar icons or to use of these techniques are geometry pre-processing algo- hot-keys in order pan, rotate, zoom, and enter certain rithms that extend the existing “primitive” algorithm. entity (e.g. surface, volume, curve, vertex) selection Many-to-one sweeping and multi-sweeping involve ex- modes when using the non-marking interface. To ex- truding surface meshes from multiple source surfaces, ecute a decomposition command, users had to select as opposed to the conventional sweeping algorithm appropriate tools using the WIMP GUI and then type which allows only one source surface. Volume submap- in the commands based on entity IDs. Mark-It aims ping involves breaking up volumes into sub-regions to extend meshing UIs of this type to go beyond using that are quicker and easier to mesh as separate en- the mouse in the 3D graphics window for only picking tities, instead of as a whole, using standard mapping and navigating. It allows the user to use the mouse to transformations. perform several different decomposition operations by drawing directly on a model. Another study tried to completely automate the de- composition process entirely by using a technique called Feature Recognition (FR), which was able to au- 2. RELATED WORK tomatically generate mesh-able volumes directly from a class of imported ACIS models [12]. Although the Time-to-mesh is the total time it takes to create a results of FR were impressive, the implemented sys- finite element mesh given a geometric model. A com- tem was not general enough to supplant the need for mon goal of many researchers is to minimize the time- human interaction. The implemented FR system also to-mesh. As stated above, decomposition is neces- lacked some options, such as the ability to specify au- sary because many meshing algorithms require pre- tomatic meshing patterns to guide the decomposition. Several other algorithmic approaches for reducing learning curve, however. Both the speedup and learn- time-to-mesh exist as well, and not surprisingly, none ing curve are expected in Mark-It as well. [21] only are fully automatic. [13] reduces datasets to wavelet implemented menus containing even numbers of op- representations and coefficients, but it also requires erations, where each menu contained 12 operations obtaining triangulation calculations in a lookup ta- at most, because it was determined in [22] that such ble and performing inverse wavelet transformations. a setup tended to increase user performance. Due [14] uses features on a “reference mesh” to automati- to the large number of possible decomposition com- cally generate mesh-able volumes on a desired model, mands, Mark-It was implemented as a variation of but consequently, it requires having to find the appro- such a marking menu system, using more than just priate reference meshes for specific geometries. [15], radial and straight-line marks. The number of opera- [16], [17], and [18] try to improve time-to-mesh by tions is only bounded by the number of distinct marks using an octree approach to produce an automatic, that can be recognized and learned by the user.