Terrain Synthesis by Digital Elevation Models

Terrain SynthesisTerrain Synthesisby Digital Elevation Modelsby Digital Elevation Models

Howard Zhou, Jie Sun, Greg Turk, and James M. Rehg

2006.10.05

Table of ContentsTable of Contents

1. Introduction2. Feature extraction3. Feature matching and alignment4. Patch stitching5. Conclusion

IntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

Why?Why?

Numerous applications Landscape design Flight simulators Feature film special effects Computer games


Terrain synthesisFractal model

fBm - fractional Brownian motion (Mandelbrot 1982) Midpoint displacement, recursive subdivision …(Fournier

1982, Miller 1986, Voss 1985, Lewis 1987, Szeliski, et al. 1989)

Erosion model Physical erosion simulation (Kelley, et al. 1988)

Combination of Both Fractal terrains with erosion features (Musgrave et al.

1989) Most commercial landscaping software such as Terragen,

Bryce, Vue d’seprit, and Mojoworld, etc.

Previous WorkPrevious WorkIntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

Limitation of previous terrain synthesis approaches Limited control by user

(parameter tuning) Hard to capture real terrain style

Previous WorkPrevious WorkIntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

What If ?What If ?IntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

Patch based texture synthesis Image quilting (Efros and Freeman 2001), Graphcut

(Kwatra et al. 2003)

Feature guided texture synthesis Image analogy (Hertzmann et al. 2000), Feature

matching and deformation (Zhang et al. 2003, Wu and Yu 2004)

Related WorkRelated WorkIntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

Terrain synthesis is not simply texture synthesis on height fields. Terrain synthesis must preserve global features such as

ridges and valleys. Terrain synthesis must be globally controllable. Unlike general textures, terrain doesn’t have natural

boundaries.

Terrain synthesis is not Terrain synthesis is not texture synthesistexture synthesis


First example-based terrain synthesisUser control via feature sketches.Feature-based approach to matching and

placement of large curvilinear terrain features.Tree-ordered patch placement algorithm.Multiple terrain style.

Our ContributionOur ContributionIntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

Feature Extraction Extract important terrain features (valleys, ridges, …)

Feature matching and deformation Match terrain features between user sketch and terrain

data to find candidate patch Use deformation to align features

Patch stitching Use graph cuts and Poisson interpolation to remove

visible seams between neighboring patches

ProcedureProcedureIntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

FlowchartFlowchart

Feature extraction

Matching and deformation

Patch stitching


Finding ridges and valleys Branches and Ends Path Features

Chang’s PPA algorithm (Profile recognition and polygon breaking)

Branch

End

Path

Feature Feature ExtractionExtraction


Why PPA?Why PPA?

Grand Canyon (shaded relief)

Edge detection result

PPA result


TargetConnection

Profile Recognition

PolygonBreaking

BranchReduction

PPA explainedPPA explainedIntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

Input

In actionIn action

Profile Recognition

In actionIn action

Polygon building

In actionIn action

Polygon Breaking

In actionIn action

Branch Reduction

In actionIn action

Result

In actionIn action

Feature Feature placement (tree placement (tree traversal)traversal)


Why is order Why is order important?important?

Raster-scan patch placement (ncc)

Tree traversal


Most of the time, the feature patches need alignment before they can be used.

Thin plate spline mapping for feature deformation Two sets of corresponding feature points from feature

matching Small deformation in terrain does not alter terrain style

Branch End Path

Feature Feature alignmentalignment


d : Deformation energy from TPS warping

g : Graphcut seam cost f : Feature dissimilarity i : Other user specified

constraints

Feature Patch Feature Patch MatchingMatching


SSD- based search (accelerated)

Fill the synthesized height map

Non-feature Non-feature placementplacement


GraphcutGraphcut

Graphcut Textures: Image and Video Synthesis Using Graph Cuts (Kwatra et al. 2003)


Poisson interpolationPoisson interpolation

Poisson image editing (Perez et al. 2003)

Modify the gradient and reconstruct


Mount JacksonMount Jackson

Grand CanyonGrand Canyon

Flathead National Flathead National Forest, MTForest, MT

Mount Vernon, Mount Vernon, KYKY

Middle EarthMiddle Earth

ConclusionConclusion

We’ve presented an image-based algorithm for terrain synthesis

It provides user control by intuitive sketch It preserves terrain style embedded in the original

height field


Cape Girardeau, Cape Girardeau, MO (failed)MO (failed)

ResultsResults

Show video

PPA in actionPPA in actionIntroductionIntroductionFeature extractionFeature extractionFeature matchingFeature matchingPatch stitchingPatch stitchingConclusionConclusion

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Terrain Synthesis by Digital Elevation Models