Enhancing Interactive Non-Planar Projections

of 3D Geovirtual Environments with Stereoscopic Imaging

Matthias Trapp, Haik Lorenz, Markus Jobst, Jürgen DöllnerHasso-Plattner-Institute at the University of Potsdam

True-3D in Cartography1st International Conference on 3D Maps

August 24 - 28, 2009 Dresden, Germany

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motivation geo-media technology

provides interactivity, immersion facilitates the communication of 3D geo spatial data

applications to cartography: increase immersion into 3D geovirtual environments support for depth-cues

planar stereoscopy: well understood – rendering: straight forward supported by graphics hardware / driver

non-planar stereoscopy: provides high field-of-view and image resolution 2

problem: non-planar projection surfaces

rendering of digital 3D city and landscape models: high amount of geometry and texture data real-time constraints (> 20 frames per second)

current generation of graphics hardware (GPU) no native support for non-planar projection surfaces requires specific rendering techniques classified into image, geometry, and ray-based

approaches

hardware-accelerated stereoscopic imaging: available stereo hardware modifies vertex pipeline stage cannot be used for rendering non-planar

stereoscopy3

framework - conceptual overview

1..N Stereo Mates

Stereo Rendering Component

SceneGeometry + Textures 1..N Virtual Cameras

Stereo Mate Generation

Chroma Depth Active

Output Device (Screen, Projector, Printer)

Passive ...

Planar Projection Image-basedNon-Planar Projection

Geometry-basedNon-Planar Projection

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review: image-based approach (IBA)

basic concept: dynamic cube map + screen-aligned quad image warping based on normal vectors:

3-phase rendering process:1. create/update dynamic cubemap2. setup projection shader3. render screen-aligned quad -β/2

-α/2

Fst = (s,t)β/2

0

α/2

φ

Viewport

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adapting IBA for stereoscopy basic idea for image-based non-planar projections:

create cubemaps for each virtual camera derive non-planar projection for each cube-map

examplary workflow for two stereo mates:

Layered Rendering Projection Function δP + Layer Sampling

Polygonal Scene Texture Layers Non-Planar Projection Stereo PairsLeft

Right

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review: geometry-based approach (GBA)

projection computed on a per-vertex basis ensure sufficient on-screen vertex density dynamic mesh refinement required

primitive index (e.g.

0,0,1,2,2,2,…)

step 3: indexed renderingrender each indexed primitive

into projection pieces

projection & clip matrices framebuffer

step 2: primitive replication create an index containing the respective number

of replications per input triangle

scene triangles

per-triangle replication

count

step 1: replication determination calculate and write one replication count per input

triangle

COP COP

Non-Planar Projection Surface Non-Planar Projection SurfaceApproximation (coarse)

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adapting GBA for stereoscopy straight forward approach:

setup piece-wise projection for each virtual camera render into different color-buffers additional post-processing step: layer compositing

example for stereo image pairs:

step 3: indexed renderingrender each indexed primitive into two projection

pieces (for left and right eye)

scene triangles

per-triangle replication

count

step 1: replication determination calculate and write one replication count per input

triangle

step 2: primitive replication create an index containing the respective number

of replications per input triangle

left eye framebuffer

projection & clip matrices

primitive index (e.g.

0,0,1,2,2,2,…)

right eye framebuffer

step 4: stereo compositingjoin both framebuffers into a single output image

framebuffer

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rendering active & passive stereo active stereo:

using quad-buffering usually encapsulated by graphics driver

passive stereo: anaglyph: color-buffer compositing polarized: render to framebuffer chromo-depth stereo: apply directly during rendering

Left Right

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rendering passive anaglyph - results

HITIT 10

rendering chromo-stereoscopy

nearv

rm = ƒ

rm (vclam

p )

vdt = ƒdt(V)

vclamp = ƒclamp(vdt) far

RG

B

CM

Y

RW

B

Cout =

ƒsam

ple (vrm )

cs ce

no need for generating stereo image pair color as a function of depth

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rendering chromo-stereoscopy - results

HITIT 12

applying chromo-stereoscopy GBA: straight forward application to fragment‘s

depth IBA: needs depth correction

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rendering chromo-stereoscopy - results

HITIT 14

chroma-stereoscopy issues common problems for IBA and GBA:

distribution of color can decrease stereo effect perception: facade information (texture) is altered interaction: focal plane must be adapted

Near Focal Plane Far Focal Plane

Equally Distributed

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binary comparision GBA vs. IBAComparison Criteria GBA IBA

Stereo Functionality Image Quality Rendering Performance Memory Footprint Implementation Complexity Overall Rating

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conclusions & future work conclusions:

interactive stereoscopic rendering for non-planar projections

increases immersion, thus psychological depth cues performance limited by geometric complexity of the

scene GBA outperforms IBA but IBA much easier to

implement/use

open problem: omni-directional stereo without image artifacts

future work: auto stereoscopy for non-planar projections surfaces eye tracking to adjust user‘s focal plane 17

Thank you for your attention! Questions?

Contact Matthias Trappmatthias.trapp@hpi.uni-potsdam.de

Haik Lorenzhaik-lorenz@hpi.uni-potsdam.de

Markus Jobstoffice@jobstmedia.at

Jürgen Döllnerjuergen.doellner@hpi.uni-potsdam.de Workgroup 3D Geoinformationwww.3dgi.de/

Computergraphics System Groupwww.hpi.uni-potsdam.de/doellner/

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