3D Occlusion Management
In this project, we study the problem space of occlusion in 3D environment and develop models and methods to reduce, or, in some special cases, eliminate the impact of occlusion on user efficiency and correctness in solving visual tasks. We believe that this will help improve the usability of 3D visualization on a broad scale, allowing designers to more readily adopt 3D computer graphics for their user applications without having to fear disorienting and alienating their users.
Our research on this problem is a multi-pronged approach:
- View projection manipulation. Modifying the view projection to minimize occlusion.
- Multiple views. Introducing additional views to disambiguate occlusion.
- Transparency. Utilize dynamic transparency to allow occluded objects to be visible.
- Navigation Guidance. Guide the user through 3D environments using computed tours from which all objects are visible.
- Explosion. Direct manipulation explosion techniques for discovering and accessing occluded targets.
- Awareness. Make the user aware of occluded objects through textual displays or on-scene labelling, etc.
2011 |
| Waqas Javed, KyungTae Kim, Sohaib Ghani, Niklas Elmqvist (2011): Evaluating Physical/Virtual Occlusion Management Techniques for Horizontal Displays. In: Proceedings of INTERACT, pp. 391-408, 2011. (Type: Inproceeding | Abstract | Links | BibTeX) @inproceedings{Javed2011, title = {Evaluating Physical/Virtual Occlusion Management Techniques for Horizontal Displays}, author = {Waqas Javed and KyungTae Kim and Sohaib Ghani and Niklas Elmqvist}, url = {http://www.umiacs.umd.edu/~elm/projects/occtable/occtable.pdf}, year = {2011}, date = {2011-01-01}, booktitle = {Proceedings of INTERACT}, pages = {391-408}, abstract = {We evaluate unguided and guided visual search performance for a set of techniques that mitigate occlusion between physical and virtual objects on a tabletop display. The techniques are derived from a general model of hybrid physical/virtual occlusion, and take increasingly drastic measures to make the user aware of, identify, and access hidden objects---but with increasingly space-consuming and disruptive impact on the display. Performance is different depending on the visual display, suggesting a tradeoff between management strength and visual space deformation.}, keywords = {} } We evaluate unguided and guided visual search performance for a set of techniques that mitigate occlusion between physical and virtual objects on a tabletop display. The techniques are derived from a general model of hybrid physical/virtual occlusion, and take increasingly drastic measures to make the user aware of, identify, and access hidden objects---but with increasingly space-consuming and disruptive impact on the display. Performance is different depending on the visual display, suggesting a tradeoff between management strength and visual space deformation. |
2009 |
| Niklas Elmqvist, Ulf Assarsson, Philippas Tsigas (2009): Dynamic Transparency for 3D Visualization: Design and Evaluation. In: International Journal of Virtual Reality, 8 (1), pp. 65–78, 2009. (Type: Article | Abstract | Links | BibTeX) @article{Elmqvist2009b, title = {Dynamic Transparency for 3D Visualization: Design and Evaluation}, author = {Niklas Elmqvist and Ulf Assarsson and Philippas Tsigas}, url = {http://www.umiacs.umd.edu/~elm/projects/dyntrans/dyntrans-journal.pdf, Paper https://www.youtube.com/watch?v=77N5KVbbEmQ, Youtube video http://www.slideshare.net/NickElm/employing-dynamic-transparency-for-3d-occlusion-management-design-issues-and-evaluation, Slides}, year = {2009}, date = {2009-01-01}, journal = {International Journal of Virtual Reality}, volume = {8}, number = {1}, pages = {65--78}, abstract = {Recent developments in occlusion management for 3D environments often involve the use of dynamic transparency, or \"virtual X-ray vision\", to promote target discovery and access in complex 3D worlds. However, there are many different approaches to achieving this effect and their actual utility for the user has yet to be evaluated. Furthermore, the introduction of semitransparent surfaces adds additional visual complexity that may actually have a negative impact on task performance. In this paper, we report on an empirical user study investigating these human aspects of dynamic transparency. Our implementation of the technique is an image-space algorithm built using modern programmable shaders to achieve real-time performance and visually pleasing results. Results from the user study indicate that dynamic transparency provides superior performance for perceptual tasks in terms of both efficiency and correctness. Subjective ratings are also firmly in favor of the method.}, keywords = {} } Recent developments in occlusion management for 3D environments often involve the use of dynamic transparency, or "virtual X-ray vision", to promote target discovery and access in complex 3D worlds. However, there are many different approaches to achieving this effect and their actual utility for the user has yet to be evaluated. Furthermore, the introduction of semitransparent surfaces adds additional visual complexity that may actually have a negative impact on task performance. In this paper, we report on an empirical user study investigating these human aspects of dynamic transparency. Our implementation of the technique is an image-space algorithm built using modern programmable shaders to achieve real-time performance and visually pleasing results. Results from the user study indicate that dynamic transparency provides superior performance for perceptual tasks in terms of both efficiency and correctness. Subjective ratings are also firmly in favor of the method. |
2008 |
| Niklas Elmqvist, Philippas Tsigas (2008): A Taxonomy of 3D Occlusion Management for Visualization. In: IEEE Transactions on Visualization and Computer Graphics, 14 (5), pp. 1095–1109, 2008. (Type: Article | Abstract | Links | BibTeX) @article{Elmqvist2008e, title = {A Taxonomy of 3D Occlusion Management for Visualization}, author = {Niklas Elmqvist and Philippas Tsigas}, url = {http://www.umiacs.umd.edu/~elm/projects/occmgt/occmgt-journal.pdf, Paper}, year = {2008}, date = {2008-01-01}, journal = {IEEE Transactions on Visualization and Computer Graphics}, volume = {14}, number = {5}, pages = {1095--1109}, abstract = {While an important factor in depth perception, the occlusion effect in 3D environments also has a detrimental impact on tasks involving discovery, access, and spatial relation of objects in a 3D visualization. A number of interactive techniques have been developed in recent years to directly or indirectly deal with this problem using a wide range of different approaches. In this paper, we build on previous work on mapping out the problem space of 3D occlusion by defining a taxonomy of the design space of occlusion management techniques in an effort to formalize a common terminology and theoretical framework for this class of interactions. We classify a total of 50 different techniques for occlusion management using our taxonomy and then go on to analyze the results, deriving a set of five orthogonal design patterns for effective reduction of 3D occlusion. We also discuss the \"gaps\" in the design space, areas of the taxonomy not yet populated with existing techniques, and use these to suggest future research directions into occlusion management.}, keywords = {} } While an important factor in depth perception, the occlusion effect in 3D environments also has a detrimental impact on tasks involving discovery, access, and spatial relation of objects in a 3D visualization. A number of interactive techniques have been developed in recent years to directly or indirectly deal with this problem using a wide range of different approaches. In this paper, we build on previous work on mapping out the problem space of 3D occlusion by defining a taxonomy of the design space of occlusion management techniques in an effort to formalize a common terminology and theoretical framework for this class of interactions. We classify a total of 50 different techniques for occlusion management using our taxonomy and then go on to analyze the results, deriving a set of five orthogonal design patterns for effective reduction of 3D occlusion. We also discuss the "gaps" in the design space, areas of the taxonomy not yet populated with existing techniques, and use these to suggest future research directions into occlusion management. |
2007 |
| Niklas Elmqvist, Philippas Tsigas (2007): A Taxonomy of 3D Occlusion Management Techniques. In: Proceedings of the IEEE Conference on Virtual Reality, pp. 51–58, 2007. (Type: Inproceeding | Abstract | Links | BibTeX) @inproceedings{Elmqvist2007f, title = {A Taxonomy of 3D Occlusion Management Techniques}, author = {Niklas Elmqvist and Philippas Tsigas}, url = {http://www.umiacs.umd.edu/~elm/projects/occmgt/occmgt.pdf, Paper}, year = {2007}, date = {2007-01-01}, booktitle = {Proceedings of the IEEE Conference on Virtual Reality}, pages = {51--58}, abstract = {While an important factor in depth perception, the occlusion effect in 3D environments also has a detrimental impact on tasks involving discovery, access, and spatial relation of objects in a 3D visualization. A number of interactive techniques have been developed in recent years to directly or indirectly deal with this problem using a wide range of different approaches. In this paper, we build on previous work on mapping out the problem space of 3D occlusion by defining a taxonomy of the design space of occlusion management techniques in an effort to formalize a common terminology and theoretical framework for this class of interactions. We classify a total of 25 different techniques for occlusion management using our taxonomy and then go on to analyze the results, deriving a set of five orthogonal design patterns for effective reduction of 3D occlusion. We also discuss the \"gaps\" in the design space, areas of the taxonomy not yet populated with existing techniques, and use these to suggest future research directions into occlusion management.}, keywords = {} } While an important factor in depth perception, the occlusion effect in 3D environments also has a detrimental impact on tasks involving discovery, access, and spatial relation of objects in a 3D visualization. A number of interactive techniques have been developed in recent years to directly or indirectly deal with this problem using a wide range of different approaches. In this paper, we build on previous work on mapping out the problem space of 3D occlusion by defining a taxonomy of the design space of occlusion management techniques in an effort to formalize a common terminology and theoretical framework for this class of interactions. We classify a total of 25 different techniques for occlusion management using our taxonomy and then go on to analyze the results, deriving a set of five orthogonal design patterns for effective reduction of 3D occlusion. We also discuss the "gaps" in the design space, areas of the taxonomy not yet populated with existing techniques, and use these to suggest future research directions into occlusion management. |
| Niklas Elmqvist, Philippas Tsigas (2007): View-Projection Animation for 3D Occlusion Management. In: Computers & Graphics, 31 (6), pp. 864–876, 2007. (Type: Article | Abstract | Links | BibTeX) @article{Elmqvist2007j, title = {View-Projection Animation for 3D Occlusion Management}, author = {Niklas Elmqvist and Philippas Tsigas}, url = {http://www.umiacs.umd.edu/~elm/projects/pmorph/pmorph-journal.pdf, Paper}, year = {2007}, date = {2007-01-01}, journal = {Computers & Graphics}, volume = {31}, number = {6}, pages = {864--876}, abstract = {Inter-object occlusion is inherent to 3D environments and is one of the challenges of using 3D instead of 2D computer graphics for visualization. Based on an analysis of this effect, we present an interaction technique for view-projection animation that reduces inter-object occlusion in 3D environments without modifying the geometrical properties of the objects themselves. The technique allows for smooth on-demand animation between parallel and perspective projection modes as well as online manipulation of view parameters, enabling the user to quickly and easily adapt the view to reduce occlusion. A user study indicates that the technique provides many of the occlusion reduction benefits of traditional camera movement, but without the need to actually change the viewpoint. We have also implemented a prototype of the technique in the Blender 3D modeler.}, keywords = {} } Inter-object occlusion is inherent to 3D environments and is one of the challenges of using 3D instead of 2D computer graphics for visualization. Based on an analysis of this effect, we present an interaction technique for view-projection animation that reduces inter-object occlusion in 3D environments without modifying the geometrical properties of the objects themselves. The technique allows for smooth on-demand animation between parallel and perspective projection modes as well as online manipulation of view parameters, enabling the user to quickly and easily adapt the view to reduce occlusion. A user study indicates that the technique provides many of the occlusion reduction benefits of traditional camera movement, but without the need to actually change the viewpoint. We have also implemented a prototype of the technique in the Blender 3D modeler. |
| Niklas Elmqvist, Mihail Eduard Tudoreanu, Philippas Tsigas (2007): Tour Generation for Exploration of 3D Virtual Environments. In: Proceedings of the ACM Symposium on Virtual Reality Software and Technology, pp. 207–210, 2007. (Type: Inproceeding | Abstract | Links | BibTeX) @inproceedings{Elmqvist2007i, title = {Tour Generation for Exploration of 3D Virtual Environments}, author = {Niklas Elmqvist and Mihail Eduard Tudoreanu and Philippas Tsigas}, url = {http://www.umiacs.umd.edu/~elm/projects/tourgen/tourgen.pdf, Paper https://www.youtube.com/watch?v=LRVTyoeuhpo, Youtube video}, year = {2007}, date = {2007-01-01}, booktitle = {Proceedings of the ACM Symposium on Virtual Reality Software and Technology}, pages = {207--210}, abstract = {Navigation in complex and large-scale 3D virtual environments has been shown to be a difficult task, imposing a high cognitive load on the user. In this paper, we present a comprehensive method for assisting users in exploring and understanding such 3D worlds. The method consists of two distinct phases: an off-line computation step deriving a grand tour using the world geometry and any semantic target information as input, and an on-line interactive navigation step providing guided exploration and improved spatial perception for the user. The former phase is based on a voxelized version of the geometrical dataset that is used to compute a connectivity graph for use in a TSP-like formulation of the problem. The latter phase takes the output tour from the off-line step as input for guiding 3D navigation through the environment.}, keywords = {} } Navigation in complex and large-scale 3D virtual environments has been shown to be a difficult task, imposing a high cognitive load on the user. In this paper, we present a comprehensive method for assisting users in exploring and understanding such 3D worlds. The method consists of two distinct phases: an off-line computation step deriving a grand tour using the world geometry and any semantic target information as input, and an on-line interactive navigation step providing guided exploration and improved spatial perception for the user. The former phase is based on a voxelized version of the geometrical dataset that is used to compute a connectivity graph for use in a TSP-like formulation of the problem. The latter phase takes the output tour from the off-line step as input for guiding 3D navigation through the environment. |
| Niklas Elmqvist, Mihail Eduard Tudoreanu (2007): Occlusion Management in Immersive and Desktop 3D Virtual Environments: Theory and Evaluation. In: International Journal of Virtual Reality, 6 (2), pp. 21–32, 2007. (Type: Article | Abstract | Links | BibTeX) @article{Elmqvist2007d, title = {Occlusion Management in Immersive and Desktop 3D Virtual Environments: Theory and Evaluation}, author = {Niklas Elmqvist and Mihail Eduard Tudoreanu}, url = {http://www.umiacs.umd.edu/~elm/projects/balloonprobe/balloonprobe-journal.pdf}, year = {2007}, date = {2007-01-01}, journal = {International Journal of Virtual Reality}, volume = {6}, number = {2}, pages = {21--32}, abstract = {We present an empirical usability experiment studying the relative strengths and weaknesses of three different occlusion management techniques for discovering and accessing objects in information-rich 3D virtual environments. More specifically, the study compares standard 3D navigation, generalized fisheye techniques using object scaling and transparency, and the BalloonProbe interactive 3D space distortion technique. Subjects are asked to complete a number of representative tasks, including counting, pattern recognition, and object relation, in different kinds of environments and on both immersive and desktop-based VR systems. The environments include a free-space abstract 3D environment and a virtual 3D walkthrough application for a simple building floor. Our results confirm the general guideline that each task calls for a specialized interaction---no single technique performed best across all tasks and worlds. The results also indicate a clear trade-off between speed and accuracy: simple navigation was the fastest but also most error-prone technique, whereas spherical BalloonProbe and transparency-based fisheye proved the most accurate but required longer completion time, making it suitable for applications where mistakes incur a high cost.}, keywords = {} } We present an empirical usability experiment studying the relative strengths and weaknesses of three different occlusion management techniques for discovering and accessing objects in information-rich 3D virtual environments. More specifically, the study compares standard 3D navigation, generalized fisheye techniques using object scaling and transparency, and the BalloonProbe interactive 3D space distortion technique. Subjects are asked to complete a number of representative tasks, including counting, pattern recognition, and object relation, in different kinds of environments and on both immersive and desktop-based VR systems. The environments include a free-space abstract 3D environment and a virtual 3D walkthrough application for a simple building floor. Our results confirm the general guideline that each task calls for a specialized interaction---no single technique performed best across all tasks and worlds. The results also indicate a clear trade-off between speed and accuracy: simple navigation was the fastest but also most error-prone technique, whereas spherical BalloonProbe and transparency-based fisheye proved the most accurate but required longer completion time, making it suitable for applications where mistakes incur a high cost. |
| Niklas Elmqvist, Ulf Assarsson, Philippas Tsigas (2007): Employing Dynamic Transparency for 3D Occlusion Management: Design Issues and Evaluation. In: Proceedings of INTERACT, pp. 532–545, 2007. (Type: Inproceeding | Abstract | Links | BibTeX) @inproceedings{Elmqvist2007b, title = {Employing Dynamic Transparency for 3D Occlusion Management: Design Issues and Evaluation}, author = {Niklas Elmqvist and Ulf Assarsson and Philippas Tsigas}, url = {http://www.umiacs.umd.edu/~elm/projects/dyntrans/dyntrans.pdf, Paper https://www.youtube.com/watch?v=77N5KVbbEmQ, Youtube video http://www.slideshare.net/NickElm/employing-dynamic-transparency-for-3d-occlusion-management-design-issues-and-evaluation, Slides}, year = {2007}, date = {2007-01-01}, booktitle = {Proceedings of INTERACT}, pages = {532--545}, abstract = {Recent developments in occlusion management for 3D environments often involve the use of dynamic transparency, or virtual \"X-ray vision\", to promote target discovery and access in complex 3D worlds. However, there are many different approaches to achieving this effect and their actual utility for the user has yet to be evaluated. Furthermore, the introduction of semi-transparent surfaces adds additional visual complexity that may actually have a negative impact on task performance. In this paper, we report on an empirical user study comparing dynamic transparency to standard viewpoint controls. Our implementation of the technique is an image-space algorithm built using modern programmable shaders to achieve real-time performance and visually pleasing results. Results from the user study indicate that dynamic transparency is superior for perceptual tasks in terms of both efficiency and correctness.}, keywords = {} } Recent developments in occlusion management for 3D environments often involve the use of dynamic transparency, or virtual "X-ray vision", to promote target discovery and access in complex 3D worlds. However, there are many different approaches to achieving this effect and their actual utility for the user has yet to be evaluated. Furthermore, the introduction of semi-transparent surfaces adds additional visual complexity that may actually have a negative impact on task performance. In this paper, we report on an empirical user study comparing dynamic transparency to standard viewpoint controls. Our implementation of the technique is an image-space algorithm built using modern programmable shaders to achieve real-time performance and visually pleasing results. Results from the user study indicate that dynamic transparency is superior for perceptual tasks in terms of both efficiency and correctness. |
2006 |
| Niklas Elmqvist, Philippas Tsigas (2006): View Projection Animation for Occlusion Reduction. In: Proceedings of the ACM Conference on Advanced Visual Interfaces, pp. 471–475, 2006. (Type: Inproceeding | Abstract | Links | BibTeX) @inproceedings{Elmqvist2006b, title = {View Projection Animation for Occlusion Reduction}, author = {Niklas Elmqvist and Philippas Tsigas}, url = {http://www.umiacs.umd.edu/~elm/projects/pmorph/pmorph.pdf, Paper}, year = {2006}, date = {2006-01-01}, booktitle = {Proceedings of the ACM Conference on Advanced Visual Interfaces}, pages = {471--475}, abstract = {Inter-object occlusion is inherent to 3D environments and is one of the challenges of using 3D instead of 2D computer graphics for information visualization. In this paper, we examine this occlusion problem by building a theoretical framework of its causes and components. As a result of this analysis, we present an interaction technique for view projection animation that reduces inter-object occlusion in 3D environments without modifying the geometrical properties of the objects themselves. The technique provides smooth on-demand animation between parallel and perspective projection modes as well as online manipulation of view parameters, allowing the user to quickly and easily adapt the view to avoid occlusion. A user study indicates that the technique significantly improves object discovery over normal perspective views. We have also implemented a prototype of the technique in the Blender 3D modeller.}, keywords = {} } Inter-object occlusion is inherent to 3D environments and is one of the challenges of using 3D instead of 2D computer graphics for information visualization. In this paper, we examine this occlusion problem by building a theoretical framework of its causes and components. As a result of this analysis, we present an interaction technique for view projection animation that reduces inter-object occlusion in 3D environments without modifying the geometrical properties of the objects themselves. The technique provides smooth on-demand animation between parallel and perspective projection modes as well as online manipulation of view parameters, allowing the user to quickly and easily adapt the view to avoid occlusion. A user study indicates that the technique significantly improves object discovery over normal perspective views. We have also implemented a prototype of the technique in the Blender 3D modeller. |
| Niklas Elmqvist, Mihail Eduard Tudoreanu (2006): Evaluating the Effectiveness of Occlusion Reduction Techniques for 3D Virtual Environments. In: Proceedings of the ACM Symposium on Virtual Reality Software and Technology, pp. 9-18, 2006. (Type: Inproceeding | Abstract | Links | BibTeX) @inproceedings{Elmqvist2006a, title = {Evaluating the Effectiveness of Occlusion Reduction Techniques for 3D Virtual Environments}, author = {Niklas Elmqvist and Mihail Eduard Tudoreanu}, url = {http://www.umiacs.umd.edu/~elm/projects/balloonprobe/balloonprobe-full.pdf, Paper https://www.youtube.com/watch?v=ynqG3JE6744, Youtube video}, year = {2006}, date = {2006-01-01}, booktitle = {Proceedings of the ACM Symposium on Virtual Reality Software and Technology}, pages = {9-18}, abstract = {We present an empirical usability experiment studying the relative strengths and weaknesses of three different occlusion reduction techniques for discovering and accessing objects in information-rich 3D virtual environments. More specifically, the study compares standard 3D navigation, generalized fisheye techniques using object scaling and transparency, and the BalloonProbe interactive 3D space distortion technique. Subjects are asked to complete a number of different tasks, including counting, pattern recognition, and object relation, in different kinds of environments with various properties. The environments include a free-space abstract 3D environment and a virtual 3D walkthrough application for a simple building floor. The study involved 16 subjects and was conducted in a three-sided CAVE environment. Our results confirm the general guideline that each task calls for a specialized interaction---no single technique performed best across all tasks and worlds. The results also indicate a clear trade-off between speed and accuracy; simple navigation was the fastest but also most error-prone technique, whereas spherical BalloonProbe proved the most accurate but required longer completion time, making it suitable for applications where mistakes incur a high cost.}, keywords = {} } We present an empirical usability experiment studying the relative strengths and weaknesses of three different occlusion reduction techniques for discovering and accessing objects in information-rich 3D virtual environments. More specifically, the study compares standard 3D navigation, generalized fisheye techniques using object scaling and transparency, and the BalloonProbe interactive 3D space distortion technique. Subjects are asked to complete a number of different tasks, including counting, pattern recognition, and object relation, in different kinds of environments with various properties. The environments include a free-space abstract 3D environment and a virtual 3D walkthrough application for a simple building floor. The study involved 16 subjects and was conducted in a three-sided CAVE environment. Our results confirm the general guideline that each task calls for a specialized interaction---no single technique performed best across all tasks and worlds. The results also indicate a clear trade-off between speed and accuracy; simple navigation was the fastest but also most error-prone technique, whereas spherical BalloonProbe proved the most accurate but required longer completion time, making it suitable for applications where mistakes incur a high cost. |
2005 |
| Niklas Elmqvist (2005): BalloonProbe: Reducing Occlusion in 3D using Interactive Space Distortion. In: Proceedings of the ACM Symposium on Virtual Reality Software and Technology, pp. 134–137, 2005. (Type: Inproceeding | Abstract | Links | BibTeX) @inproceedings{Elmqvist2005a, title = {BalloonProbe: Reducing Occlusion in 3D using Interactive Space Distortion}, author = {Niklas Elmqvist}, url = {http://www.umiacs.umd.edu/~elm/projects/balloonprobe/balloonprobe.pdf, Paper https://www.youtube.com/watch?v=ynqG3JE6744, Youtube video}, year = {2005}, date = {2005-01-01}, booktitle = {Proceedings of the ACM Symposium on Virtual Reality Software and Technology}, pages = {134--137}, abstract = {Using a 3D virtual environment for information visualization is a promising approach, but can in many cases be plagued by a phenomenon of literally not being able to see the forest for the trees. Some parts of the 3D visualization will inevitably occlude other parts, leading both to loss of efficiency and, more seriously, correctness; users may have to change their viewpoint in a non-trivial way to be able to access hidden objects, and, worse, they may not even discover some of the objects in the visualization due to this inter-object occlusion. In this paper, we present a space distortion interaction technique called the BalloonProbe which, on the user’s command, inflates a spherical force field that repels objects around the 3D cursor to the surface of the sphere, separating occluding objects from each other. Inflating and deflating the sphere is performed through smooth animation, ghosted traces showing the displacement of each repelled object. Our prototype implementation uses a 3D cursor for positioning as well as for inflating and deflating the force field \"balloon\". Informal testing suggests that the BalloonProbe is a powerful way of giving users interactive control over occlusion in 3D visualizations.}, keywords = {} } Using a 3D virtual environment for information visualization is a promising approach, but can in many cases be plagued by a phenomenon of literally not being able to see the forest for the trees. Some parts of the 3D visualization will inevitably occlude other parts, leading both to loss of efficiency and, more seriously, correctness; users may have to change their viewpoint in a non-trivial way to be able to access hidden objects, and, worse, they may not even discover some of the objects in the visualization due to this inter-object occlusion. In this paper, we present a space distortion interaction technique called the BalloonProbe which, on the user’s command, inflates a spherical force field that repels objects around the 3D cursor to the surface of the sphere, separating occluding objects from each other. Inflating and deflating the sphere is performed through smooth animation, ghosted traces showing the displacement of each repelled object. Our prototype implementation uses a 3D cursor for positioning as well as for inflating and deflating the force field "balloon". Informal testing suggests that the BalloonProbe is a powerful way of giving users interactive control over occlusion in 3D visualizations. |