Modelling

Ruth Aylett

Overview

  Basic issues –  Modelling packages –  Low polygon modelling –  Importing models

  Buildings –  Photogrammetry –  Laser range finders –  LIDAR

  The great outdoors –  Cheap methods

3D Authoring tools

  Most models produced with generic 3D modelling packages offline

  Some packages derive from film/animation: –  Maya, 3DStudioMax, Softimage, Rhino, Blender, AC3D.

–  creation of realistic creatures or backgrounds for film or games industries.

–  Not designed for creating real-time rendered models

  Others from science/technology:

–  Matlab, PV-WAVE, AutoCAD.

–  Not designed for realistic textures, lighting etc

  Integrated with game engine: Unreal Tournament, Never Winter Nights, Unity etc

  All packages create objects, give them styles, assign behaviours and place them in 3D Cartesian space.

Other VR Software Tools

  DI Guy - Boston Dynamics   Poser – Metacreations   Simulink - Mathworks   Vizard – WorldViz (sits on OSG)   CityEngine – ESRI   Specialised terrain modelling (many)

3D Studio Max

  3D Studio Max (or 3ds max) - Autodesk –  Probably biggest selling professional 3D content

creation package.

  Many special purpose plugins such as Character Studio.

  Still relatively expensive –  PC only for a long time Much used in film

Low polygon modelling

  Realtime constraints require working to a ‘polygon budget’

–  See http://www.webreference.com/3d/lesson52/ for an example

–  Also http://cg.tutsplus.com/tutorials/game-art/sculpt-model-and-texture-a-low-poly-skull-in-blender/

Use of texture   Make low-poly model look better   Normal maps

–  Implementation of bump mapping –  Fake lighting of bumps and dents –  RGB image "

•  corresponds to X, Y, and Z coords of a surface normal from more detailed version of object"

  True v ‘fake’ bump mapping"–  True = perturb geometry (affects

silhouette)"–  Fake = apply to normals only"

•  Can be calculated in real-time on graphics card"

Using level of detail (LOD)

  Produce different versions of same object –  Very low polygon versions to be used when distant –  5000 polygons in one view is often plenty –  Using texture can help

Obtaining texture images

  Libraries from software – 3DS Max, Maya etc

  Web – www.3dcafe.com

  Camera with Photoshop editing

Texture photography

  Orthogonal pictures are best (but physically impossible)

  If the camera has a zoom function – zoom in as far as possible – stand well back –  this gives photos that are as close as

possible to being orthogonal

Texture photography

  If the camera has a manual / automatic control then use it – particularly important for white balance

  A series of photos taken on automatic will have a different setting for white balance for each photo and the colours will not balance

Texture photography

  Avoid using the flash if you can   It is better to have light evenly

distributed across the object you are photographing

  Direct flash light is often uneven, particularly if close up

Photo editing in Photoshop

  The best tools for texture editing are photo touch up packages like Adobe Photoshop

  These packages allow the user to –  Distort the texture

•  perspective in photos taken at an angle

–  Rub out unwanted features in the texture •  passing traffic •  undesirable reflections

–  Create tileable textures   The aim is to create a clean, orthogonal,

(maybe repeating) image

Importing models -1

  Always an issue –  Given use of separate modelling and runtime

software

  Some formats are widely imported by runtime systems –  3ds and vrml 1.0

  Use of VRML 1.0 –  x3D can be exported in VRML syntax –  But VRML 2.0 (the ISO standard) added:

•  Animation, user interaction etc •  So these must be removed

Importing models - 2

  Geometry is not the only problem –  Textures often problematic –  64 or 128 bit squares often required –  Use of texture tiling (see fields of X3D Texture

node)

  Games engines may be idiosyncratic –  E.g Unreal Tournament had a ‘carve out’

approach to modelling

Scaling up

  Hand construction of models is slow – Modelling packages give limited support

  Can modelling be automated? How much? – Buildings? – Whole cities? – Terrain?

  Games companies need to cut costs

What makes a ‘good’ model?

  Trade-off between polygon count, accuracy, and effort

  Depends on the application –  Virtual heritage: as accurate as possible!

•  Low polygon statues?

–  City •  Effort dominates •  Iconic v standard buildingss

–  Physically-based models •  Model behaviour is key

Modelling buildings

  Use architects’ drawings –  By hand: slow but accurate?

  Photogrammetry –  Use cameras on the real thing?

  Google earth example: /attach/faedd5360530f7b5/149169.kmz?gda=KMdbB0YAAACy_T8H3t6cdbII2AqXSUBfp4Ui5Sbfi9qzEsC9zM0-w_vtILYQn0OAisJ7OWVTjK1x40jamwa1UURqDcgHarKEE-Ea7GxYMt0t6nY0uV5FIQ&pli=1&part=3

  Laser scanning from models   LIDAR data

Architects’ drawings

  The obvious approach, BUT – Not always available – Require a long manual model construction – As-built not always as-designed

Photogrammetry

Processing the data

  Manual identification of approx 12 points in all 3 views –  Use of accurate knowledge of focal length and

negative size –  Can calculate exact distance of camera from scene –  See http://en.wikipedia.org/wiki/Photogrammetry

for software list

Laser rangefinding

  Use of laser beam to gather distance information –  time-of-flight: the round trip travel time of a single

pulse is measured and distance calculated based on the speed of light

–  Can also capture reflectance data

Laser Scanning Range Finder

  Real World Capture   Conversion of range data

– Range 2.5m - 80+m – Accuracy 2mm - 10+cm

The Liverpool Project

  Use laser scanner to scan the physical model

  Create VE model of a model

The Process -Build the Model   Select area to scan

–  1 overall - 5 perspectives @ 4mm intervals –  4 sections - 4 perspectives each @ 2mm intervals

  Nearly 2 million points in the clouds

  Segmentation –  Hierarchy - areas, buildings, planes –  Fit surfaces

  10,000 Polygons

The Liverpool Model

Creating the dinosaurs from the BBC TV series using Laser Scanning

Advantages: Fast, Accurate, Can be automated Disadvantage: Expensive, Large output file, Can be hazardous

LIDAR

  Light Detection And Ranging – Airbourne laser rangefinding – Using known position, altitude, orientation

of plane

Data collection

  Collects position (x,y) and elevation (z) –  At pre-determined intervals –  Accuracy depend son flying height, laser beam

diameter, GPS quality, post-processing –  Accuracy up to +- 15cms elevation –  No need to select specific scanning targets

The great outdoors

  Human artefacts are the easiest thing to model –  Lots of planes, often orthogonal –  Thus low-polygon models

  But grass? Bushes? Trees? Flowers? –  One polygon for each blade of grass? Several for

each leaf?

  Water? Clouds? Fire?   Flesh? Fur? Hair?

Cheap methods

  All involve compromises with appearance   Water:

–  Use a water texture: of course it doesn’t move •  Sunken blue shape

–  Create some polygons and a colour animation •  This can look like flow

Trees

  Billboard with tree texture on it –  Looks the same from any angle

  Two polygons at 90 degrees with tree texture on them

  There are commercially available models   And a few free ones: e.g xfrog public plant

• See http://web.inf.tu-dresden.de/ST2/cg/downloads/publicplants/