Declarative Specification of Declarative Specification of Ambiance in VRML Ambiance in VRML

LandscapesLandscapes

Vincent Jolivet, Dimitri Plemenos, Patrick Poulingeas.Vincent Jolivet, Dimitri Plemenos, Patrick Poulingeas.

MSI Laboratory.MSI Laboratory.

University of Limoges (France).University of Limoges (France).

Declarative Specification of Declarative Specification of Ambiance in VRML LandscapesAmbiance in VRML Landscapes

IntroductionIntroductionDeclarative ModellingDeclarative ModellingManaging declarative specifications with Managing declarative specifications with

fuzzy subsets theoryfuzzy subsets theoryApplication to the foggy aspect of a sceneApplication to the foggy aspect of a sceneApplication to natural lightingApplication to natural lightingConclusionConclusion

An overview of VRMLAn overview of VRML

VRML has now become a standard for VRML has now become a standard for creating creating virtualvirtual worlds integrated to worlds integrated to Internet.Internet.

VRML offers to the designer high-level VRML offers to the designer high-level objects and manages all the rendering objects and manages all the rendering process. process.

VRML is an open text-based format which VRML is an open text-based format which allows a processing by script languages.allows a processing by script languages.

VRML tools VRML tools There are 2 types of tools for a VRML designer:There are 2 types of tools for a VRML designer: Geometric modellersGeometric modellers (for the static aspect of a (for the static aspect of a

virtual world).virtual world). Behavorial modellersBehavorial modellers (for the dynamic aspect of a (for the dynamic aspect of a

virtual world).virtual world).

Our goal is to present an improvement ofOur goal is to present an improvement ofgeometric modellers when the virtual world isgeometric modellers when the virtual world isa landscape.a landscape. A perspective similar to the aim of A perspective similar to the aim of Declarative ModellingDeclarative Modelling

Declarative ModellingDeclarative Modelling

The aim of declarative modelling is to The aim of declarative modelling is to produce several prototypes of scenes produce several prototypes of scenes corresponding to a high-level and vague corresponding to a high-level and vague specification.specification.

There are 2 kinds of declarative modellers:There are 2 kinds of declarative modellers:General purpose declarative modellersGeneral purpose declarative modellers for any for any

kind of scenes.kind of scenes.Dedicated declarative modellersDedicated declarative modellers specialized in specialized in

a domain (This work belongs to this class).a domain (This work belongs to this class).

Phases of Declarative ModellingPhases of Declarative Modelling

1.1. Description phaseDescription phase (where the designer (where the designer describes her wishes in a “natural” and describes her wishes in a “natural” and declarative manner). declarative manner).

2.2. Scene generation phaseScene generation phase (where an (where an algorithm generates all the scenes algorithm generates all the scenes satisfying the description).satisfying the description).

3.3. Scene understanding phaseScene understanding phase (where the (where the solutions found are shown to the user solutions found are shown to the user with a classification method).with a classification method).

Managing PropertiesManaging Properties

Declarative specifications use properties.Declarative specifications use properties.Properties have an inherent imprecision.Properties have an inherent imprecision. Words like “big” or “tall” do not correspond Words like “big” or “tall” do not correspond

to a precise numerical interval.to a precise numerical interval.Fuzzy subsets theory can take into Fuzzy subsets theory can take into

account this imprecision due to natural account this imprecision due to natural language.language.

This theory can also build new properties This theory can also build new properties with modifiers and a few basic properties.with modifiers and a few basic properties.

Two kinds of propertiesTwo kinds of properties

Simple propertiesSimple properties (“The weather is foggy”). (“The weather is foggy”). These properties are qualitative.These properties are qualitative.

Parametric propertiesParametric properties (“The level of snow (“The level of snow is 2 meters”).is 2 meters”).

These properties introduces a numerical These properties introduces a numerical value.value.

Fuzzy Representation of PropertiesFuzzy Representation of Properties

Simple and parametric properties are Simple and parametric properties are represented by trapezoidal membership represented by trapezoidal membership

functions in our usage of fuzzy-subsets theory.functions in our usage of fuzzy-subsets theory.

• [a,b] is the kernel of the membership function.• [a-α,b+β] is the support of the membership function.

Generate Numeric Values Generate Numeric Values for a Propertyfor a Property

1.1. A threshold A threshold αα is fixed. is fixed.

2.2. The The αα-support set of the membership -support set of the membership function associated to the property is function associated to the property is computed computed An interval. An interval.

3.3. A discretization of the computed interval A discretization of the computed interval gives several values (gives several values ( several several solutions) solutions)

ModifiersModifiers

Modifiers are operators that act on Modifiers are operators that act on simple simple propertiesproperties to create a new property. to create a new property.

Modifiers are:Modifiers are:Extremely littleExtremely littleVery littleVery littleRather littleRather little (( No modification of the simple property) No modification of the simple property)RatherRatherVeryVeryExtremely Extremely

Action of a Modifier on Action of a Modifier on a Simple Propertya Simple Property

The simple property “weak” is plotted in red.

Fuzzy OperatorsFuzzy Operators

Fuzzy operators act both on Fuzzy operators act both on simple and simple and parametric propertiesparametric properties to create a new to create a new property.property.

Fuzzy operators are:Fuzzy operators are:ExactlyExactlyReallyReally (( No modification of the property) No modification of the property)NeighboringNeighboringMore or lessMore or lessVaguelyVaguely

Uncertainty in DescriptionsUncertainty in Descriptions

Previous descriptions were Previous descriptions were impreciseimprecise..A new kind of descriptions has been A new kind of descriptions has been

introduced: descriptions with introduced: descriptions with uncertaintyuncertainty..Example of such descriptions: “It is Example of such descriptions: “It is ratherrather

certaincertain that the level of snow is 2 meters”. that the level of snow is 2 meters”.The word “rather” acts as an uncertainty The word “rather” acts as an uncertainty

operator which can increase or decrease operator which can increase or decrease the uncertainty of the description.the uncertainty of the description.

Uncertainty operatorsUncertainty operators

Uncertainty operators can be used with Uncertainty operators can be used with simple and parametric propertiessimple and parametric properties to create to create a new property.a new property.

The following set of uncertainty operatorsThe following set of uncertainty operatorshave been chosen:have been chosen:

(means that the description is certain)(means that the description is certain)RatherRatherEnoughEnoughLittleLittleVery littleVery little

Action of an uncertainty Operator Action of an uncertainty Operator on a Propertyon a Property

There is a reduction of the size of the kernel of the membership function (of the basic property) and a contraction of this function.

Foggy Scenes in VRMLFoggy Scenes in VRML

VRML allows the designer to change the VRML allows the designer to change the foggy aspect of a scene with a Fog node.foggy aspect of a scene with a Fog node.

The Fog node has a The Fog node has a visibility fieldvisibility field which which corresponds to the visibility limit for the corresponds to the visibility limit for the Avatar.Avatar.

Properties for foggy AspectProperties for foggy Aspect

2 kinds of properties are proposed to the2 kinds of properties are proposed to the

designer:designer:A A simple propertysimple property like “The weather is like “The weather is

foggy”.foggy”.A A parametric propertyparametric property like “The visibility like “The visibility

limit is 50 meters”.limit is 50 meters”.

Examples of Solutions foundExamples of Solutions found

The visibility limit is 70 meters The visibility limit is exactly 70 meters

Action of an operator on a property

Examples of Solutions foundExamples of Solutions found

First scene found for the description Last scene found for the description

Several solutions are computed for the same description: “The visibility limit is 70 meters”.

Natural Lighting in a SceneNatural Lighting in a Scene

VRML proposes a node called VRML proposes a node called DirectionalLight for a scene illumination.DirectionalLight for a scene illumination.

This node introduces a This node introduces a directional lightdirectional light in in the VRML landscapes.the VRML landscapes.

This directional light will correspond to the This directional light will correspond to the light of the sun. light of the sun.

The lived TimeThe lived Time

To express the natural lighting in a To express the natural lighting in a declarative manner, the concept of declarative manner, the concept of

“ “lived timelived time” (D. Siret) has been chosen.” (D. Siret) has been chosen. In a geocentric model, the possible sun In a geocentric model, the possible sun

positions are computed from descriptions positions are computed from descriptions such as:such as: ““The end of the afternoon” ;The end of the afternoon” ; ““Beginning of the day in Winter” ;Beginning of the day in Winter” ; ““The end of the morning in the middle of The end of the morning in the middle of

Summer”. Summer”.

Determination of the Sun PositionDetermination of the Sun Position

A geocentric model (Figure taken from a work of D. Siret).

Intervals corresponding to Intervals corresponding to the “lived Time”the “lived Time”

Figure taken from a work of D. Siret.

Example of natural LightingExample of natural Lighting

One scene corresponding to the description: “Midday”.

Example of natural LightingExample of natural Lighting

One scene corresponding to the description: “The middle of the afternoon”.

Drawbacks of the MethodDrawbacks of the Method

The drawbacks come from VRML limitations.The drawbacks come from VRML limitations.

Absence of shadows (damages the realism Absence of shadows (damages the realism of sun lighting).of sun lighting).

Lighting included in textures becomes Lighting included in textures becomes inconsistent when the sun position inconsistent when the sun position changes.changes.

Impossibility to introduce complex physical Impossibility to introduce complex physical parameters. parameters.

Future ResearchesFuture Researches

In order to overcome the previous drawbacks:In order to overcome the previous drawbacks:Lighting in textures can be recovered and Lighting in textures can be recovered and

changed with an inverse rendering process.changed with an inverse rendering process.VRML viewers like Contact of Blaxxun have VRML viewers like Contact of Blaxxun have

interesting extensions of VRML standard interesting extensions of VRML standard (e.g. Particle and MultiTexture nodes)(e.g. Particle and MultiTexture nodes)

The emergence of X3D would give more The emergence of X3D would give more possibilities than VRML. possibilities than VRML.

ConclusionConclusion

A framework to manage declarative A framework to manage declarative descriptions has been introduced.descriptions has been introduced.

This framework is based on fuzzy subset This framework is based on fuzzy subset theory.theory.

An application to ambiance in VRML An application to ambiance in VRML landscapes has been presented.landscapes has been presented.

This framework can be reused for handling This framework can be reused for handling ambiance in more generic scenes. ambiance in more generic scenes.