interactive inverted perspective rendering for...

Interactive Inverted Perspective Rendering for Architectural

Visualization

Vinod SrinivasanOzan Ozener

Ergun Akleman

Visualization Sciences ProgramDepartment of Architecture

Texas A&M University

2005June 20th – 22ndVienna University of TechnologyVienna, Austria

June 21, 2005Interactive Inverted Perspective Rendering

for Architectural Visualization2

Outline

BackgroundInteractive Inverted PerspectiveInteractive Non-Photorealistic DisplayThree-dimensional ModelingImplementationConclusions



Background

Normal perspective– Distant objects perceived as being smaller than closer

objects– Used to convey depth in 2D artwork

Inverted perspective– Illusion of depth perception where depth cues are reversed– Distant parts are shown larger than nearer ones– Also uses a linear projection but with a different center of

projection



Background

Inverted perspective (contd.)– Static 2D images don’t necessarily convey this

effectWe interpret that the smaller objects are far away and larger ones are closerIf viewer knows relative positions through other means, a static 2D image can be enoughCan be confusing since what is seen is contrary to what viewer expects to see



Background

Inverted perspective (contd.)– Inverted perspective effect becomes more

pronounced when there is relative motion between viewer and scene

– Changing angle of view causes scene to change in an unexpected way



Background

Inverted perspective in art– Explored by artists as far back as 16th century– More recent – work of Patrick Hughes

Referred to as “reverse perspective” or “reverspective”

Several theories for motivation and reasoning behind such illustrations– Of recent interest to perceptual psychologists– One viewpoint: Inverse perspective conveys more

information than linear perspective



Background

Architectural design– Normal perspective projection has been widely

used throughout the ages– Digital media has opened up new avenues for

creative expression– Production of complex perspectives possible in a

digital mediumCan enhance production & representation of conceptual spaces



Background

Architectural design & visualization in digital age– Need for new digital tools and techniques for

advanced representation, design & visualization– Inverted perspective is one such visualization

technique



Background

Work of Vallance & Calder– 2001: Computer interface to facilitate multi-

perspective rendering, including reverse perspective

Implementation too slow for interactive visualizationInvolves an entire API

– 2003: Technique for rendering inward looking projections (“anti-perspective projection”)

Results are very similar to inverted perspective images



Interactive Inverted Perspective

Typical 3D graphics application– User can see parts of the object “pointing towards” him/her– In terms of mesh structure, faces whose normals point

towards the viewer are displayed“Front-facing” vs. “back-facing”

– Hidden surfaces are not shown – eliminated using depth (distance from viewer along viewing direction)

Faces which are in “front” obscure faces which are in the “back”.




Typical 3D graphics application (contd.)– Visible faces change when viewer moves through

the scene and viewpoint changes“Front-facing” and “back-facing” faces change“Front” faces and “back” faces change




Inverted Perspective Effect– Switch the faces that are shown– “Front-facing” faces are not displayed and “back-

facing” faces are shown– Hidden-surface removal

Visible faces “hide” faces which are “behind” them




Inverted perspective rendering of a particular view– Switch to inverted perspective rendering– Rotate object/scene so we are still looking at the

same faces that were visible in normal perspective

– The switch is usually not readily seen– Rotating the scene makes the inverted

perspective effect apparent



Interactive Non-Photorealistic Display

For conceptual design ability to see the interior elements of a structure is usefulWireframe representation provides a fully transparent model view– Not effective in terms of understanding spatial

configuration and boundary structure– Does not convey depth information effectively– Can become very complicated for models with

large number of faces




Other display methods for showing interior structure– Move viewpoint inside the exterior surface

Can view either interior of the exterior in a single image, not both

New display method to show both interior and exterior simultaneously– Based on transformation used for inverted

perspective display




Switch the set of faces that are shown– “Front-facing” faces are not shown, “back-facing”

faces are seenInterior layout is visible

Overlay a wireframe representation of “front-facing” faces on top of above imageHidden-surface removal is still usedInterior portions are seen and wireframe gives a good idea of the exterior shape



Three-dimensional Modeling

Modification to non-photorealistic rendering method– Allows easy modeling of complex structures

Show wireframe for entire mesh instead of just the “front-facing” faces– Wireframe is required for being able to select

faces, edges and vertices for modeling operations



Implementation

All techniques presented have been incorporated into our topological mesh modeling system– System provides basic modeling & interactive

rendering capabilities– Includes several other tools for creating structures

with beams, columns, holes and handles



Implementation

Interactive inverted perspective display and wireframe overlay can be toggled on or off using hotkeysSoftware is written in C++Uses OpenGL for graphics and FLTK for user-interfaceDeveloped on Linux, ported to Windows using Cygwin



Demo



Contributions

An easy-to-use system which allows the viewer to explore inverted perspective in an interactive mannerTools for architectural modeling and visualization– Inverted-perspective visualization is useful for

better understanding of conceptual models– 3D modeling tool effective for creating objects

with fairly complicated interior structures



Future Work

Handle complicated nested structures such as a building layout with interior walls– Reverse normals of the interior elements

appropriatelyGives a “cut-section” type of view



Future Work



Future Work

Explore use of inverted perspective display in a virtual reality environmentAbility to apply the various display modes to selected surfaces rather than the whole sceneUse “depth-peeling” to view surfaces at different depths– Can be done in real time on the GPU



Questions?

Vinod Srinivasan, Assistant ProfessorOzan Ozener, Ph.D. studentErgun Akleman, Associate Professor{vinod,ozan,ergun}@viz.tamu.edu

Visualization Sciences ProgramDepartment of ArchitectureTexas A&M Universityhttp://www-viz.tamu.edu

interactive inverted perspective rendering for...

Documents