EMERGING TRENDS IN TERRAIN VISUALIZATION

- Suchitra Manepalli

OUTLINE

GIS Evolution VRML Terrain Modeling Data and Compression Algorithms Implications Conclusion

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TERMS

Georeference: existence in a physical space Polygons, lines, points

Map projection: mathematical means of transferring information from a model of earth (3D) to a flat surface (2D)

Pixel: smallest individual unit of an image Resolution: accuracy of depicting the location

and shape of map features Geodatabase: database with extension for

storing, creating, editing spatial and geographic information

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EXAMPLE

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GIS HISTORY

Geographical referenced information analyze spatial information

Cartography, Resource Management, Environmental Impact Assessment

GIS started by Ontario, Canada Federal department of Forestry and Rural

Development Canada Land Inventory

Tomlinson: Father of GIS

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VRML Virtual Reality Modeling Language, an ISO

Standard and web standard High level object oriented language VRML world can be accessed using standard

browsers Text file format where vertices and edges are

specified with following properties Surface color Mapped textures Shininess Transparency

Widely used as a file format for interchange of 3D models

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VRML

LOD level for deep level hierarchies Low resolution can be traded for higher

resolution VRML with XML demonstrated GeoVRML UTM coordinate system can add scientific

content 3D terrain on the web

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GIS BASICS

Data creation – digitized from a hard copy of a map or a survey

Different types of information and sources in many different forms

Represents real world objects with digital data

Two types of data: Raster: any type of digital image, rows and

columns of cells, a color value Vector: geographical features as vectors using

geometrical shapes

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RASTER

Matrix of cells in a continuous space Cell size direct correlation with map Impact the ordering of spatial data Three types of raster data:

thematic data – digital elevation model spectral data – aerial or satellite imagery

vegetation geologic information pictures – normal day to day

Vectorization: raster to vector, GIS

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VECTOR

Positional data in form of coordinates

Vector data basic units of spatial information

Best used to store discrete and well defined data

Vector operations are allowed Rotation, movement, mirroring, sketching, affine,

z-order Shading algorithms: Phong, Gouraud Rasterization: Conversion of vector data to

raster data

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WHICH TYPE OF DATA?

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Pixel size defines resolution

Efficient for dense data – elevation

Large amounts of storage space

Easy creation from image data

Precision of coordinates defines resolution

Efficient for sparse data – hospitals or highways

Processing requires lots of computer time

High resolution

Raster Vector

TERRAIN MODELING HISTORY

First models for military Topographic maps were rare, problem to

create the third dimensional model to a two dimensional map

World War II – allied produced terrain models using different techniques

Several techniques on cardboard existed Plaster models, pantograph, wenschow,

vaccumforming, terrain emboss, computer based techiques

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TERRAIN MODELING BASICS

3D GIS models use terrain modeling 3D terrain model consists of two main things:

Digital Elevation Model: topography of the terrain Geographical information: satellite images, aerial

photographs etc Connecting the points – a polygon based 3D

representation of terrain Texture mapping a model Interpolation technique such as Gourarud

Shading

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TERRAIN MODELING TECHNOLOGIES Google Earth and Microsoft Virtual Earth

Organizational framework Digital terrain modeling: 3D surface computed

from a set of points Representations: Regular Grid and Triangular Irregular

Network 3D Terrain Visualization: Earth observation image

data on digital elevation models RealityMap: Visualize unlimited spatial extents

incorporating gigabytes of imagery, modeling and elevation

TerraVista: Standalone, modeler independent, database for 3D creation

Flooding, earthquake disasters are modeled

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TERRAIN MODELING TRENDS

Improvements in scientific and commercial purposes

Hydrology – water flows accuracy, flood damage and flood extent

Marine observations – coastal change and storm impacts

Geological land observations – landslides, avalanches

Accurate elevation data – automated driver assistance by responding to their surroundings

Terrain model in war and space

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DIGITAL ELEVATION MODEL

Developed and maintained by NIMA File content – uniform 2D array of values Raster type – cell represents 30m pixel size

with the elevation value assigned to the cell 5 different levels: level increases resolution

increases Extract slope and aspect DEM – topographic elevations sampled on a

uniform grid spacing DEM will produce a better model than

digitized contours

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DATA COMPRESSION TECHNIQUES

Gigabytes of storage Transmission of data DEM Data

Wavelet transformation Lossy compression of elevation data using SPIHT

DEM Compression Linear prediction Statistical encoding

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JPEG2000 - IMAGE COMPRESSION

JPEG2000 – new standard for compression of data

Supports 38 bits per band Suitable for DTED

Significant changes in intensity and/or color Kakadu

DTED Compression ROI capability within JPEG2000 High level compression Perfect reproduction of DTED file along an

arbitrary path

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JPEG2000 - REVIEW

Resending unnecessary information eliminated

No numerical loss along the defined region Allows XML data to be included in the file

header File header in form SVG – read and overlaid

on image during decoding Reduced storage and dissemination resource

requirements

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FUTURE GROWTH

Keyhole, TerraServer, TerraFly – visualize whole earth with specific regions with different resolutions Keyhole – 3D visualization

Extends to Mars Space Spin – New digital terrain model for

Mars

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IMPLICATIONS

Google sued for invasion of privacy – street view

Google talking to Canada How much detail is too much detail?

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CONCLUSION

GIS evolution has improved over the years Terrain modeling started off as a military

project Many compression techniques for data and

image Visual analysis is always the better way!

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QUESTIONS

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