Illustrative

Shadows

Integrating

and

Information

Displays

Many

exploration

and

manipulation

tasks

benefit

from

a

coherent

integration

of

multiple

views

onto

complex

information

spaces

This

paper

proposes

the

concept

of

Illustrative

Shadows

for

a

tight

integration

of

interactive

graphics

and

schematic

depictions

using

the

shadow

metaphor

The

shadow

metaphor

provides

an

intuitive

visual

link

between

and

visualizations

integrating

the

different

displays

into

one

combined

information

display

Users

interactively

explore

spatial

relations

in

realistic

shaded

virtual

models

while

functional

correlations

and

additional

textual

information

are

presented

on

additional

projection

layers

using

a

semantic

network

approach

Manipulations

of

one

visualization

immediately

influence

the

others

resulting

in

an

in-formationally

and

perceptibly

coherent

presentation

H.

-LSB-

Information

Interface

and

Presentation

-RSB-

User

Interfaces

Screen

design

I.

-LSB-

Artificial

Intelligence

-RSB-

Knowledge

Representation

Formalisms

and

Methods

Semantic

networks

I.

-LSB-

Computer

Graphics

-RSB-

Methodology

and

Techniques

Interaction

techniques

Design

Human

Factors

In

many

areas

knowledge

about

structures

and

their

meaning

as

well

as

their

spatial

and

functional

relations

are

required

to

comprehend

possible

effects

of

an

intervention

For

example

engineers

must

understand

the

construction

of

machines

as

a

prerequisite

for

maintenance

whereas

the

spatial

composition

of

molecules

and

hence

possible

reactions

are

of

importance

for

the

discovering

of

new

drugs

in

chemistry

Medical

students

need

to

imagine

the

wealth

of

spatial

and

functional

correlations

within

the

human

body

to

master

anatomy

To

date

novices

as

well

as

domain

experts

are

required

to

consult

several

often

voluminous

documents

in

parallel

to

extract

information

for

a

certain

intervention

Spatial

relations

characteristics

of

structures

inherently

three-dimensional

such

as

the

shape

and

location

of

structures

however

are

difficult

to

convey

on

paper

Besides

requiring

a

significant

amount

of

images

to

illustrate

spatial

relations

between

only

a

few

structures

the

mental

integration

of

multiple

views

to

form

a

three-dimensional

picture

in

mind

is

demanding

Spatial

relations

can

be

conveyed

more

ef-fectively

by

means

of

models

-LSB-

-RSB-

Using

interactive

graphics

available

to

more

and

more

people

due

to

recent

advances

in

consumer

graphics

hardware

the

user

may

actively

explore

the

spatial

correlations

of

structures

within

a

photorealistic

virtual

model

-LRB-

see

upper

left

of

Figure

-RRB-

Here

the

visual

realism

of

the

model

facilitates

recognition

on

real

encounters

Information

about

functional

correlations

such

as

the

interplay

of

muscles

causing

an

upward

motion

of

the

human

foot

has

been

traditionally

provided

by

means

of

text

and

illustrations

as

found

in

textbooks

Simple

non-photorealistic

drawings

enriched

with

annotations

and

metagraphical

symbols

can

be

extremely

powerful

in

conveying

complex

relationships

and

procedures

-LRB-

see

upper

right

of

Figure

-RRB-

Abstraction

techniques

reduce

the

complexity

of

the

depicted

structures

to

illustrate

the

important

aspects

thereby

guiding

the

attention

of

the

viewer

to

relevant

details

In

contrast

to

the

visualization

of

spatial

relations

graphics

add

no

significant

value

to

the

illustration

of

functional

correlations

Figure

Illustrative

Shadows

provide

an

intuitive

visual

link

between

spatial

-LRB-

-RRB-

and

non-spatial

-LRB-

-RRB-

information

displays

integrating

them

into

one

combined

information

display

M.

tibialis

anterior

M.

extensor

hallucis

longus

M.

extensor

digitorum

longus

M.

tibialis

posterior

M.

flexor

digitorum

longus

M.

flexor

hallucis

longus

M.

fibularis

brevis

M.

fibularis

longus

interactive

display

shadow

Permission

to

make

digital

or

hard

copies

of

all

or

part

of

this

work

for

personal

or

classroom

use

is

granted

without

fee

provided

that

copies

are

not

made

or

distributed

for

profit

or

commercial

advantage

and

that

copies

bear

this

notice

and

the

full

citation

on

the

first

page

To

copy

otherwise

or

republish

to

post

on

servers

or

to

redistribute

to

lists

requires

prior

specific

permission

and/or

a

fee

IUI

January

Miami

Florida

USA

Copyright

ACM

The

integration

of

both

aspects

in

one

visualization

is

difficult

since

each

serves

to

fulfill

a

different

goal

with

partly

mutually

exclusive

visualization

techniques

It

becomes

even

more

complicated

if

the

model

is

frequently

manipulated

such

as

in

construction

or

recent

interactive

learning

environments

Here

occludings

by

annotations

and

metagraphical

symbols

are

annoying

and

may

even

interrupt

the

current

manipulation

for

the

user

Additional

views

whether

as

insets

-LSB-

-RSB-

separate

objects

like

mirrors

-LSB-

-RSB-

or

in

form

of

lenses

and

volumetric

cursors

changing

the

rendition

of

embedded

structures

-LSB-

-RSB-

are

either

not

close

enough

to

the

manipulated

structures

to

be

fully

recognized

without

dividing

the

users

attention

between

different

views

-LSB-

-RSB-

or

require

sometimes

tedious

manipulations

to

be

placed

or

moved

within

the

scene

Nonetheless

additional

information

as

to

restrictions

or

functional

correlations

pertaining

the

current

manipulated

structures

is

highly

desired

even

necessary

In

this

paper

we

present

an

approach

called

Illustrative

Shadows

that

provides

an

intuitive

visual

link

between

an

actively

manipulated

visualization

and

a

supplemental

information

display

integrating

them

into

one

combined

information

display

-LRB-

see

Figure

-RRB-

One

of

the

main

ideas

behind

Illustrative

Shadows

is

the

integration

of

secondary

information

or

in

other

words

background

information

into

an

interactive

scene

By

analyzing

the

users

manipulation

of

structures

and

finding

correlations

graphical

and

textual

information

about

the

current

interaction

context

such

as

graphical

object-details

and

textual

labels

are

displayed

in

the

background

the

shadow

to

give

guidance

as

well

as

to

further

enhance

the

users

understanding

of

the

context

The

paper

is

structured

as

follows

After

reviewing

related

approaches

to

combine

multiple

visual

and

textual

information

displays

we

present

the

design

of

Illustrative

Shadows

Furthermore

an

architecture

realizing

these

concepts

is

discussed

in

this

section

Thereafter

the

major

components

of

this

architecture

are

described

Realization

issues

are

subject

of

the

subsequent

section

whereas

application

examples

and

the

summary

conclude

the

paper

Recently

proposed

tools

for

the

exploration

of

virtual

scenes

extend

possibilities

to

display

covered

structures

or

hidden

details

A

complementary

view

called

Magic

Mirror

that

mimics

a

hand

mirror

has

been

introduced

in

-LSB-

-RSB-

In

addition

to

providing

the

optical

effects

of

a

real

mirror

it

also

allows

to

explore

the

insight

of

objects

by

clipping

against

the

mirror

front-frustum

Magic

lens

filters

as

presented

in

-LSB-

-RSB-

go

further

by

combining

an

arbitrarily-shaped

region

with

an

operator

that

changes

the

view

of

objects

viewed

through

that

region

thereby

displaying

different

aspects

of

the

visualized

information

space

In

-LSB-

-RSB-

the

lens

approach

is

extended

to

using

volumetric

lenses

All

aforementioned

techniques

require

the

user

to

actively

manipulate

a

tool

within

the

scene

These

techniques

assume

the

user

already

knows

which

parts

of

the

presented

visualization

offer

additional

information

or

is

willing

to

explore

the

model

While

this

might

be

feasible

in

explorative

environments

where

navigation

is

the

main

interaction

task

it

certainly

hinders

manipulation

Several

approaches

to

combine

and

visualizations

have

been

made

using

a

corner

cube

environment

-LRB-

-RRB-

The

three

orthogonal

sides

show

image

slices

that

provide

a

visual

context

for

a

model

or

structures

displayed

in

the

center

In

-LSB-

-RSB-

the

images

have

been

integrated

as

back-planes

to

ground

the

representation

of

anatomic

structures

visually

By

outlining

the

structures

in

the

images

the

spatial

correspondence

between

the

renditions

of

activated

foci

in

the

context

of

human

brain

slices

is

emphasized

in

-LSB-

-RSB-

The

images

however

are

precomputed

and

do

not

change

according

to

the

users

interaction

nor

is

there

any

visualization

of

functional

correlations

An

interesting

interactive

approach

has

been

proposed

by

-LSB-

-RSB-

The

projection

of

the

model

onto

the

sides

of

the

corner

cube

can

be

manipulated

by

the

user

in

order

to

change

the

position

and

orientation

of

the

model

Fully

rendered

shadows

of

certain

objects

resemble

real-world

mirrors

and

may

be

used

to

stress

importance

There

is

however

no

discussion

on

how

to

use

this

feature

to

provide

for

instance

additional

context

information

for

the

user

To

establish

hypotheses

on

the

interaction

context

in

order

to

be

able

to

display

additional

context

information

and

to

provide

meaningful

descriptions

of

relationships

knowledge

modeling

is

required

Promising

approaches

to

connect

those

knowledge

with

graphics

have

been

developed

in

the

area

of

medical

applications

The

Digital

Anatomist

-LSB-

-RSB-

incorporates

a

logic-based

description

comprising

class

and

subclass

relationships

-LRB-

is-a

-RRB-

as

well

as

partitive

and

qualitative

spatial

relationships

-LRB-

has-parts

is-superior

to

-RRB-

The

information

is

presented

in

tree-like

textual

form

that

can

be

explored

by

folding

and

unfolding

Corresponding

structures

are

displayed

in

a

visualization

aside

There

is

no

visual

integration

of

both

information

displays

The

semantic

network

described

in

-LSB-

-RSB-

is

used

to

create

various

views

in

which

correlating

structures

are

displayed

to

communicate

specific

aspects

with

a

voxel

model

of

the

human

anatomy

The

highly

detailed

visualization

however

can

not

be

interactively

explored

nor

is

there

any

kind

of

abstraction

to

focus

the

users

attention

Interaction

is

only

possible

by

tree-like

menus

With

the

term

Illustrative

Shadows

we

refer

to

a

coherent

integration

of

photorealistic

depictions

of

a

virtual

model

with

abstract

illustrations

and

textual

explanations

Both

Figure

Architecture

of

a

system

incorporating

the

Illustrative

Shadows

approach

model

visualization

visualization

Visualization

annotations

Knowledge

based

server

Client

interface

System

Event

control

kinds

of

depictions

serve

to

fulfill

different

and

somehow

contradicting

goals

on

the

one

hand

to

enable

navigation

and

manipulation

of

complex

spatial

models

and

on

the

other

hand

to

provide

adjusted

visualizations

that

guide

the

user

's

attention

to

additional

information

about

the

most

relevant

objects

in

the

current

interaction

context

Both

visualizations

are

achieved

by

applying

photorealistic

and

specific

non-photorealistic

rendering

techniques

-LSB-

-RSB-

to

geometric

models

Furthermore

textual

information

describing

the

most

relevant

structures

and

functional

correlations

between

them

must

be

integrated

The

estimation

of

the

relevance

with

respect

to

the

current

interaction

context

as

well

as

the

selection

or

generation

of

textual

explanations

heavily

rely

on

non-geometric

formal

and

informal

representations

and

are

therefore

determined

by

external

inference

mechanisms

Moreover

co-referential

relations

between

the

entities

within

the

geometric

model

and

the

formal

and

informal

representations

have

to

be

established

in

order

to

link

the

different

representations

Based

on

these

requirements

we

designed

a

system

architecture

which

comprises

three

basic

components

-LRB-

see

Figure

-RRB-

The

visual

component

renders

a

photorealistic

model

with

a

standard

camera

model

as

well

as

a

non-photorealistic

illustration

that

is

projected

onto

a

ground

plane

A

client

interface

enables

external

control

of

the

non-photorealistic

rendering

techniques

Finally

the

visual

component

also

renders

text

and

metagraphical

annotations

such

as

labels

hypertext

and

arrows

The

event

control

allows

the

user

to

modify

the

parameters

of

a

virtual

camera

and

to

select

and

manipulate

geometric

objects

within

the

scene

Interactions

are

tracked

and

ranked

within

an

interaction

history

to

communicate

the

current

interaction

context

via

a

client

interface

to

an

external

knowledge-based

component

The

knowledge-based

server

receives

notification

of

user

manipulations

and

establishes

hypotheses

on

the

degree

of

interest

values

-LRB-

DOI

-RRB-

for

geometric

objects

These

DOI

values

guide

the

selection

of

appropriate

text

fragments

presented

in

text

annotations

as

well

as

the

modification

of

parameters

of

the

non-photorealistic

rendering

techniques

for

emphasizing

in

the

illustration

The

following

sections

discuss

important

aspects

of

these

system

components

Besides

displaying

a

photorealistic

rendition

of

a

model

that

the

user

can

manipulate

the

illustration

of

functional

correlations

between

structures

of

the

model

in

the

background

has

to

be

accomplished

To

focus

the

user

's

attention

on

relevant

structures

and

to

facilitate

perception

important

objects

must

be

emphasized

and

surroundings

abstracted

Furthermore

both

visualizations

must

be

integrated

in

a

coherent

manner

so

that

a

visual

connection

between

the

and

renditions

of

the

relevant

objects

is

established

by

the

user

Several

crucial

aspects

have

to

be

considered

How

can

objects

be

emphasized

such

that

they

attract

the

user

's

attention

while

still

being

in

the

background

Are

additional

graphical

elements

required

to

establish

a

visual

correlation

between

the

two

model

representations

What

illustration

techniques

can

be

applied

to

differentiate

between

important

and

less

important

objects

Is

a

continuous

synchronization

between

the

photorealistic

and

the

schematic

representation

of

the

model

necessary

during

user

interactions

Integrating

Different

Model

Representations

The

question

coming

up

at

this

point

is

how

a

secondary

schematic

model

representation

can

be

integrated

such

that

the

following

requirements

are

fulfilled

The

second

representation

must

be

placed

near

the

original

representation

in

order

to

perceive

structures

in

both

representations

-LSB-

-RSB-

The

secondary

representation

may

never

occlude

the

central

realistic

visualization

which

a

user

manipulates

directly

The

relevant

information

however

must

be

visible

in

order

to

be

recognized

but

should

not

distract

from

the

interaction

with

the

model

An

exact

copy

of

the

model

representation

is

not

appropriate

for

the

task

of

depicting

functional

correlations

because

their

illustration

in

the

background

requires

abstraction

Without

abstraction

a

lot

of

the

users

attention

would

be

required

to

extract

the

relevant

information

An

exact

copy

however

can

be

used

to

provide

a

mirrored

view

below

the

model

to

visualize

structures

otherwise

not

visible

for

the

user

-LRB-

see

Figure

at

the

end

-RRB-

The

integration

of

a

secondary

view

as

inset

-LSB-

-RSB-

has

some

disadvantages

too

Firstly

the

inset

must

not

occlude

the

model

thus

it

must

be

placed

in

distance

which

in

turn

means

visual

separation

Secondly

the

inset

framing

complicates

the

visualization

of

object

correlations

e.g.

by

lines

An

ideal

solution

in

many

respects

is

to

project

the

model

onto

a

plane

below

the

model

just

like

casting

a

shadow

This

representation

may

then

be

modified

in

various

ways

to

illustrate

associated

concepts

and

relations

and

therefore

is

called

Illustrative

Shadows

Besides

this

approach

satisfies

the

requirements

specified

above

Illustrative

Shadows

Cast

shadows

-LSB-

-RSB-

have

proven

to

be

beneficial

for

perceiving

spatial

relationships

and

to

facilitate

object

positioning

Figure

Different

types

of

model

projections

onto

the

illustration

plane

Beside

simple

monochrome

projections

-LRB-

shadows

-RRB-

the

color

of

individual

structures

can

be

preserved

The

mirrored

projection

shows

details

otherwise

hidden

in

the

current

view

Monochrome

projection

Colored

projection

Mirrored

projection

-LSB-

-RSB-

Thus

their

use

if

already

present

occupies

no

additional

space

for

the

display

of

additional

information

or

in

the

case

of

prior

absence

also

add

valuable

depth

cues

to

the

visualization

Furthermore

the

shadows

can

be

used

to

interact

with

the

underlying

information

context

or

as

proposed

in

-LSB-

-RSB-

with

the

shadowing

objects

To

sum

up

The

shadow

projection

results

in

an

abstraction

which

is

very

important

for

illustrations

Additional

depth

cues

facilitate

the

perception

of

spatial

relations

and

accelerate

the

relative

positioning

of

objects

while

manipulating

the

model

The

projection

establishes

a

link

between

a

object

and

its

shadow

providing

additional

information

Displaying

and

Focusing

in

the

Illustration

Plane

Besides

simple

monochrome

shadow

projection

further

possibilities

to

project

the

model

representation

onto

the

illustration

plane

come

to

mind

-LRB-

see

Figure

-RRB-

Preserving

the

colors

of

the

different

structures

of

the

model

for

instance

enables

distinct

renditions

and

perception

of

the

objects

in

the

shadow

As

an

extension

the

objects

can

be

mirrored

before

projecting

them

Hence

objects

or

hidden

details

of

objects

otherwise

not

visible

become

visible

in

the

illustration

plane

To

illustrate

correlations

or

to

annotate

structures

the

relevant

objects

must

be

emphasized

to

be

easily

distinguished

from

the

remaining

visualization

Also

the

viewer

must

be

able

to

differentiate

between

relevant

and

less

relevant

objects

For

monochrome

shadow

projections

the

object

color

must

contrast

with

the

shadow

color

The

selection

of

emphasizing

colors

should

be

based

on

a

perception

oriented

color

model

such

as

the

HSV

Moreover

an

outline

can

be

used

to

attract

the

viewer

's

interest

A

colored

projection

makes

it

somewhat

more

difficult

since

the

variation

of

the

color

wo

n't

always

result

in

a

noticeable

distinct

representation

By

using

a

conspicuous

texture

or

shaded

representations

of

the

relevant

object

whereas

the

remaining

objects

are

flat-shaded

the

viewer

's

attention

can

be

directed

to

those

relevant

objects

Significance

of

Accentuations

In

addition

to

objects

being

significant

to

the

current

interaction

context

supplementary

objects

have

to

be

included

in

the

illustration

These

objects

are

not

of

primary

importance

within

the

concepts

to

be

illustrated

but

guide

the

viewer

and

maintain

context

It

is

important

that

such

objects

are

recognized

by

the

viewer

as

objects

of

minor

significance

The

relevance

of

objects

that

have

been

emphasized

by

outlining

for

instance

can

be

judged

by

line

width

or

line

style

-LRB-

e.g.

contrast

waviness

-RRB-

Also

preserving

the

objects

color

as

well

as

the

use

of

texture

indicates

a

higher

importance

than

an

interpolation

of

the

object

's

color

and

the

background

color

Recognition

of

Correlations

between

both

Representations

An

important

aspect

in

using

two

different

but

coherent

representations

of

the

same

model

is

the

identification

of

correlations

between

those

visualizations

by

the

viewer

If

an

object

is

being

emphasized

in

the

illustration

plane

it

must

be

possible

for

the

viewer

to

find

its

counterpart

in

the

detailed

photorealistic

representation

too

Often

shape

and

color

give

enough

hints

However

if

the

projection

of

the

relevant

objects

results

in

uniform

shapes

the

viewer

may

have

difficulties

to

recognize

individual

objects

in

the

visualization

-LRB-

see

Figure

-RRB-

Besides

accentuating

those

objects

in

the

representation

the

integration

of

additional

elements

can

be

beneficial

Semi-transparent

shadow

volumes

originally

developed

to

facilitate

object

positioning

in

-LSB-

-RSB-

indicate

direct

correspondence

-LRB-

see

Figure

-RRB-

Integration

of

Annotations

The

conveyance

of

important

related

facts

by

means

of

graphical

abstraction

accentuation

or

modification

of

relevant

structures

alone

is

difficult

Therefore

conventional

book

illustrations

often

contain

annotations

with

short

descriptions

Those

annotations

must

be

placed

close

to

the

described

objects

and

should

not

occlude

relevant

parts

of

the

presentation

The

latter

however

can

not

always

be

guaranteed

A

simple

but

effective

solution

places

the

annotation

on

a

semi-transparent

background

face

that

increases

the

contrast

between

text

annotation

and

illustration

and

still

does

not

block

vision

-LRB-

see

Figure

-RRB-

To

further

facilitate

absorption

of

shown

concepts

single

words

or

groups

of

words

can

be

emphasized

and

graphically

linked

to

relating

structures

in

the

illustration

Hypertext

functionality

reduces

the

amount

to

which

textual

annotations

must

be

displayed

at

once

The

user

can

request

more

detailed

information

by

activating

links

Figure

Recognition

of

individual

objects

in

different

scenes

To

the

left

unequivocal

correspondence

of

shape

and

color

facilitates

identification

To

the

right

no

clear

correspondence

Figure

A

direct

connection

to

an

object

's

shadow

is

established

by

displaying

its

semi-transparent

shadow

volume

The

integration

of

annotations

gives

meaning

to

unknown

objects

and

relationships

A

human

illustrator

is

required

to

identify

important

aspects

and

characteristic

features

of

the

subject

or

concept

that

is

to

be

conveyed

in

order

to

draw

a

focussed

visualization

One

way

to

identify

those

features

for

the

computer

is

to

watch

the

user

interacting

with

the

information

space

Since

our

goal

has

been

to

enhance

the

users

understanding

by

providing

background

information

in

the

current

interaction

context

an

Illustrative

Shadow

depicting

correlations

in

that

context

must

be

generated

By

navigating

within

the

model

on

the

one

hand

the

user

is

free

to

explore

spatial

relations

by

changing

the

view

Here

single

structures

may

be

tracked

by

the

computer

regarding

their

visibility

hence

obtaining

information

about

the

users

current

focus

On

the

other

hand

the

user

may

interact

with

the

structures

thus

expressing

specific

interest

As

a

result

of

the

integrated

visualization

interaction

is

possible

within

the

visualization

as

well

as

in

the

projection

layers

a

technique

inspired

by

-LSB-

-RSB-

Using

the

shadow

for

interaction

facilitates

certain

tasks

such

as

selection

since

structures

hidden

in

the

visualization

may

be

visible

in

the

projection

Furthermore

input

device

coordinates

can

be

mapped

directly

onto

the

plane

thereby

enabling

the

use

of

interaction

techniques

The

provided

manipulation

tasks

highly

depend

on

the

application

that

employs

the

concept

of

Illustrative

Shadows

In

our

application

the

user

is

able

to

compose

and

to

decompose

a

given

model

like

a

jigsaw

Thus

translation

and

rotation

of

individual

structures

are

main

interaction

tasks

User-interactions

are

tracked

within

an

interaction

history

By

assigning

relevance

values

to

each

interaction

task

accumulations

of

these

values

show

a

distribution

of

interest

within

the

model

over

time

Thus

each

single

structure

's

degree

of

interest

-LRB-

DOI

a

normalized

value

-RRB-

is

a

measure

for

its

importance

to

the

user

at

a

certain

time

As

shown

in

Table

touching

a

structure

with

the

mouse

pointer

has

a

much

lower

relevance

than

actually

selecting

it

The

degree

of

interest

is

communicated

to

the

knowledge

server

which

in

turn

may

modify

the

visualization

of

the

shadow

To

give

an

example

the

user

is

interested

in

a

certain

structure

of

an

anatomic

visualization

such

as

a

ligament

that

is

part

of

a

functional

relation

between

a

bone

and

a

muscle

Only

one

of

those

objects

that

is

the

bone

or

the

muscle

should

be

highlighted

and

annotated

because

of

space

restrictions

in

the

shadow

layer

At

this

point

the

DOI

is

used

to

decide

If

the

interaction

history

shows

more

user-interest

for

muscles

information

about

the

functional

relation

between

the

ligament

and

the

muscle

is

displayed

While

segmentation

of

the

model

into

individual

structures

-LRB-

objects

-RRB-

provides

a

spatial

description

the

presentation

of

correlations

also

requires

a

linked

symbolic

textual

description

Moreover

in

order

to

establish

hypotheses

on

the

current

interaction

context

formal

knowledge

is

required

Thus

the

system

presented

in

this

paper

comprises

a

knowledge

base

i.e.

a

media-independent

formal

representation

media-specific

realization

statements

of

entities

within

the

formal

representation

as

well

as

a

large

multi-lingual

text

corpus

Realization

statements

establish

co-reference

relations

between

independent

formal

representations

describing

different

aspects

of

the

underlying

information

space

They

also

guide

the

generation

or

selection

of

texts

used

to

annotate

structures

in

the

visualization

The

medical

education

application

presented

later

in

this

paper

is

based

on

a

knowledge

base

describing

the

objects

and

functional

correlations

of

the

musculo-skeletal

system

It

covers

the

area

of

the

lower

limb

and

the

pelvic

girdle

The

knowledge

base

was

created

by

manually

analyzing

several

anatomy

textbooks

anatomy

atlases

medical

dictionaries

and

lexica

This

analysis

reveals

important

concepts

their

hierarchical

classification

and

the

instance

attribute

values

forming

a

complex

semantic

network

Our

system

contains

a

hierarchical

representation

of

basic

anatomic

concepts

such

as

bones

muscles

articulations

tendons

as

well

as

their

parts

and

regions

The

corpus

contains

fragments

of

several

anatomic

textbooks

describing

global

concepts

of

the

osteology

syndesmology

and

myology

as

well

as

descriptions

of

all

the

entities

of

these

anatomic

systems

within

the

lower

leg

and

the

pelvic

girdle

In

order

to

present

appropriate

system

reactions

the

event

control

informs

the

knowledge

server

of

user

interactions

First

exploiting

the

visual

annotations

the

knowledge

action

parameter

value

relevance

mouseOver

time

short

long

mouseButtonPressed

location

object

object

annotation

Table

Relevance

of

certain

user

interactions

Figure

Visualization

of

intermediate

steps

within

a

retrieval

which

discovers

the

association

between

the

distal

phalanx

of

the

big

toe

and

the

extensor

hallucis

longus

has-Basis

has-Area

has-Basis

Os-Longum

Bone-Basis

Musculus

Bone-Area

Phalanx

distalis

pedis

Basis

phalangis

distalis

pedis

Area

insertion

of

M.

extensor

hallucis

longus

M.

extensor

hallucis

longus

Instance

Relation

Concept

server

extracts

co-referring

formal

entities

and

assigns

relevance

values

according

to

Table

Subsequently

the

knowledge

server

searches

for

associations

between

the

most

relevant

entities

Our

system

pursues

two

alternative

strategies

retrievals

and

suggestions

Retrievals

discover

relations

between

entities

by

tracking

predefined

paths

within

the

knowledge

base

Figure

illustrates

the

intermediate

steps

in

order

to

extract

relations

between

bones

and

muscles

From

a

functional

point

of

view

-LRB-

i.e.

the

muscle

mechanics

-RRB-

bones

are

insertions

or

origins

of

muscles

Its

contraction

produces

force

which

in

turn

changes

the

orientation

of

these

bones

These

retrievals

also

need

to

consider

substructures

-LRB-

e.g.

bone-volumes

and

bone-area

-RRB-

The

following

retrieval

extracts

those

muscles

which

originate

in

a

given

bone

-LRB-

first

logic

order

-RRB-

The

has-Part

relation

represents

the

transitive

hull

over

several

spatial

part-of-relations

-LSB-

-RSB-

-LRB-

e.g.

the

has-Basis

relation

between

Bones

and

Bone-Volumes

and

the

has-Area

relation

between

Areas

or

Volumes

and

Areas

-RRB-

These

retrievals

rely

on

knowledge

about

the

structure

of

the

knowledge

base

Moreover

they

refer

to

a

small

number

of

relevant

objects

In

many

situations

however

the

event

control

comes

up

with

a

huge

number

of

potential

relevant

objects

which

can

not

easily

be

mapped

to

a

predefined

query

Hence

we

adopt

a

bottom-up

search

approach

within

a

complex

semantic

network

developed

within

cognitive

psychology

In

his

model

of

human

comprehension

-LSB-

-RSB-

Quillian

assumed

that

spatially

and

temporally

independent

aspects

of

human

long-term

memory

are

organized

in

a

semantic

network

Furthermore

he

assumed

that

cognitive

processes

that

access

a

node

of

the

semantic

network

activate

all

connected

nodes

in

parallel

The

term

spreading

activation

refers

to

a

recursive

propagation

of

initial

stimuli

Nowadays

this

term

subsumes

breadth-first

search

algorithms

for

paths

connecting

the

nodes

of

a

start

and

a

destination

set

in

directed

graphs

satisfying

an

evaluation

criterion

Collins

and

Loftus

-LSB-

-RSB-

modify

the

propagation

algorithm

to

consider

activation

strength

In

our

system

the

knowledge

server

uses

the

objects

DOI

from

the

event

control

as

an

initial

activation

which

spreads

through

the

semantic

network

These

initial

activa-tions

also

take

the

content

presented

on

textual

labels

and

inspected

by

the

user

into

account

The

spreading

activation

approach

generates

a

focus

structure

which

contains

information

how

dominant

graphical

objects

must

be

presented

in

the

schematic

illustration

-LSB-

-RSB-

Figure

illustrates

how

visual

dominance

values

control

the

render

parameters

The

visual

component

of

the

prototypical

implementation

extends

the

Open

Inventor

graphical

library

with

powerful

scenegraph

nodes

to

display

hypertext

on

overlay

regions

and

to

render

semi-transparent

shadow

volumes

Other

nodes

encapsulate

the

mirror

and

shading

projection

onto

the

ground

plane

as

well

as

the

user

interaction

and

emphasize

techniques

-LRB-

e.g.

computation

of

silhouette

lines

-RRB-

The

layer

management

-LRB-

see

Figure

-RRB-

employs

the

OpenGL

polygon

offset

feature

to

allow

graphics

to

overlap

specifically

whereas

visibility-tests

of

individual

structures

are

accomplished

by

offscreen

rendering

and

analyzing

OpenGL

p-buffers

Additional

OSF

Motif

widgets

enable

the

user

to

add

personalized

annotations

which

are

inserted

into

the

knowledge

base

The

knowledge

base

encodes

both

the

media-independent

formal

knowledge

representation

as

well

as

media

specific

realization

statements

using

XML

topic

maps

-LSB-

-RSB-

To

process

this

information

XML

statements

are

transformed

into

LISP-code

The

authoring

system

contains

export

filters

for

the

NeoClassic

and

the

LOOM

-LSB-

-RSB-

description

logic

inference

machine

In

the

current

version

it

covers

about

basic

anatomic

concepts

relations

and

over

instances

with

linguistic

realization

statements

in

Latin

German

and

English

Furthermore

visual

annotations

refer

to

a

small

number

of

geometric

models

and

illustrations

The

interface

between

the

knowledge

server

and

the

visual

component

is

described

using

CORBA

's

interface

definition

language

-LRB-

IDL

-RRB-

The

CORBA-based

interface

implementation

enables

us

to

experiment

with

several

knowledge

serv-Figure

Application

of

different

emphasize

techniques

to

the

information

representation

according

to

decreasing

dominance

values

-LCB-

muscle

bone

Bone

-LRB-

bone

-RRB-

Musculus

-LRB-

muscle

-RRB-

-LRB-

is-Origin-of

-LRB-

bone

muscle

-RRB-

part

has-Part

-LRB-

bone

part

-RRB-

is-Origin-of

-LRB-

part

muscle

-RRB-

-RRB-

-RCB-

Figure

Multiple

layers

are

used

to

place

the

different

visual

information

in

order

Thereby

occluded

details

may

be

visible

in

the

shadow

-LRB-

-RRB-

Outline

Highlight

Ordinary

Detail

Annotation

ers

implemented

in

Common-LISP

-LRB-

LOOM

-RRB-

and

C++

-LRB-

NeoClassic

-RRB-

We

applied

the

concept

of

Illustrative

Shadows

to

an

application

of

medical

education

This

system

had

been

previously

designed

to

foster

the

understanding

of

spatial

relationships

by

means

of

models

based

on

a

virtual

jigsaw

approach

-LSB-

-RSB-

While

composing

anatomical

structures

has

proven

to

help

medical

students

to

build

an

understanding

of

the

spatial

composition

-LSB-

-RSB-

most

of

the

users

expressed

their

desire

for

detailed

information

about

functional

relations

between

structures

Consequently

students

would

be

able

to

playfully

study

human

organs

including

their

spatial

and

functional

correlations

Figures

and

depict

the

screen

of

the

prototype

in

typical

learning

sessions

Individual

objects

can

be

detached

and

moved

within

the

scene

to

expose

occluded

structures

In

Figure

one

of

the

alternative

visualization

the

mirror

is

shown

to

demonstrate

the

various

employments

of

the

plane

It

enables

the

user

to

simultaneously

look

at

two

different

views

of

the

model

Graphical

accentuations

are

used

to

attract

the

viewer

's

attention

-LRB-

left

atrium

-RRB-

Additional

textual

annotations

are

assigned

to

correlating

structures

in

a

hypertext

representation

which

can

be

explored

by

following

sepa-rately

marked

links

Another

application

that

has

not

yet

been

realized

is

to

support

users

of

CAD

systems

by

Illustrative

Shadows

CAD

systems

are

not

only

used

to

design

individual

components

in

but

also

to

assemble

complex

systems

Information

about

parameters

of

single

components

and

relationships

are

of

major

importance

Being

able

to

retrieve

this

information

directly

from

the

scene

while

interacting

with

the

components

is

of

great

benefit

for

the

design

engineer

For

educational

engineering

or

maintenance

purposes

a

wealth

of

information

about

spatial

and

functional

correlation

as

well

as

textual

information

is

required

In

this

paper

we

developed

a

new

metaphor-based

approach

to

coher-ently

integrate

different

views

onto

such

a

complex

information

space

within

an

interactive

system

Illustrative

Shadows

provide

an

intuitive

visual

link

and

a

level

of

integration

between

interactive

graphics

and

supplemental

information

displays

that

is

hard

to

achieve

with

other

concepts

Shadow

projections

have

proven

to

be

beneficial

for

perceiving

spatial

relationships

and

to

facilitate

object

positioning

Thus

their

use

if

already

present

occupies

no

additional

space

for

the

display

of

additional

information

or

in

the

case

of

prior

absence

also

add

valuable

depth

cues

to

the

visualization

The

shadow

projection

onto

a

flat

plane

enables

schematic

illustrations

which

are

focused

on

specific

information

extraction

tasks

and

facilitates

the

integration

of

generated

textual

information

that

leads

to

further

meaning

Thus

Illustrative

Shadows

promote

the

comprehension

of

complex

spatial

relations

and

functional

correlations

Furthermore

the

secondary

information

display

does

not

hinder

manipulations

of

the

model

Our

approach

is

well

suited

for

compact

models

and

has

been

successfully

applied

to

an

application

of

medical

education

Bernauer

J.

Analysis

of

Part-Whole

Relation

and

Subsumption

in

the

Medical

Domain

Data

Knowledge

Engineering

-LRB-

-RRB-

October

Biezunski

M.

Bryan

M.

and

Newcomb

S.

editors

ISO/IEC

Topic

Maps

Information

Technology

Document

Description

and

Markup

Language

International

Organization

for

Standarization

Figure

Alternative

visualization

The

Mirror

facilitates

manipulation

in

by

providing

a

better

view

of

the

structures

The

central

representation

is

never

occluded

by

annotations

Figure

German

annotation

of

objects

previously

selected

Realization

statements

of

the

semantic

network

provide

alternative

German

English

and

Latin

phrases

referring

to

formal

entities

-LRB-

ISO

-RRB-

and

International

Electrotechnical

Commission

-LRB-

IEC

-RRB-

December

Draft

Blinn

J.F.

Me

and

my

-LRB-

fake

-RRB-

shadow

IEEE

Computer

Graphics

Applications

-LRB-

-RRB-

January/Febru-ary

Brinkley

J.F.

Wong

B.A.

Hinshaw

K.P.

and

Rosse

C.

Design

of

an

Anatomy

Information

System

IEEE

Computer

Graphics

Applications

-LRB-

-RRB-

May/June

Cignoni

P.

Montani

C.

and

Scopigno

R.

Magic-sphere

An

insight

tool

for

data

visualization

IEEE

Computer

Graphics

Forum

-LRB-

-RRB-

Collins

A.

and

Loftus

E

A

Spreading-Activation

Theory

of

Semantic

Processing

Psychological

Review

-LRB-

-RRB-

Fishkin

K.

and

Stone

M.C.

Enhanced

dynamic

queries

via

moveable

filters

In

Katz

I.R.

Mack

R.

Marks

L.

Rosson

M.B.

and

Nielsen

J.

editors

Proc

of

ACM

CHI

Conference

on

Human

Factors

in

Computing

Systems

-LRB-

Denver

May

-RRB-

pages

ACM

Press

New

York

Grosjean

J.

and

Coquillart

S

The

magic

mirror

A

metaphor

for

assisting

the

exploration

of

virtual

worlds

In

Zara

J.

editor

Proc

of

Spring

Conference

on

Computer

Graphics

-LRB-

Budmerice

Slovakia

April

-RRB-

pages

Hartmann

K.

Schlechtweg

S.

Helbing

R.

and

Strothotte

T.

Knowledge-Supported

Graphical

Illustration

of

Texts

In

De

Marsico

M.

Levialdi

S.

and

Panizzi

E.

editors

Proc

of

the

Working

Conference

on

Advanced

Visual

Interfaces

-LRB-

AVI

-RRB-

pages

Trento

Italy

May

ACM

Press

New

York

Herndon

K.P.

Zeleznik

R.C.

Robbins

D.C.

Conner

D.B.

Snibbe

S.S.

and

van

Dam

A.

Interactive

shadows

In

Proc

of

ACM

Symposium

on

User

Interface

and

Software

Technology

-LRB-

Monterey

November

-RRB-

pages

ACM

Press

New

York

H

hne

K.H.

Pflesser

B.

Pommert

A.

Riemer

M.

Schiemann

T.

Schubert

R.

and

Tiede

U

A

virtual

body

model

for

surgical

education

and

rehearsal

IEEE

Computer

-LRB-

-RRB-

January

MacGregor

R

A

Description

Classifier

for

the

Predicate

Calculus

In

Hayes-Roth

B.

and

Korf

R.

editors

Proc

of

the

Twelfth

Annual

National

Conference

on

Artificial

Intelligence

-LRB-

-RRB-

pages

Seattle

Washington

August

AAAI

Press

Menlo

Park

Moreno

R.

and

Mayer

R.E.

Cognitive

principles

of

multimedia

learning

Journal

of

Educational

Psychology

Pommert

A.

H

hne

K.H.

Pflesser

B.

Richter

E.

Riemer

M.

Schiemann

T.

Schubert

R.

Schumacher

U.

and

Tiede

U.

Creating

a

high-resolution

spatial

symbolic

model

of

the

inner

organs

based

on

the

visible

human

Medical

Image

Analysis

-LRB-

-RRB-

Quillian

M.

Semantic

Memory

In

Minsky

M.

editor

Semantic

Information

Processing

chapter

pages

MIT

Press

Cambridge.

Rehm

K.

Lakshminaryan

K.

Frutiger

S.

Schaper

K.A.

Sumners

D.W.

Strother

S.C.

Anderson

J.R.

and

Rottenberg

D.A.

A

symbolic

environment

for

visualizing

activated

foci

in

functional

neuroimaging

datasets

Medical

Image

Analysis

-LRB-

-RRB-

Ritter

F.

Berendt

B.

Fischer

B.

Richter

R.

and

Preim

B.

Virtual

jigsaw

puzzles

Studying

the

effect

of

exploring

spatial

relations

with

implicit

guidance

In

Herczeg

M.

Prinz

W.

and

Oberquelle

H.

editors

Proc

of

Mensch

Computer

-LRB-

Hamburg

September

-RRB-

pages

Stuttgart

Leipzig

Wiesbaden

B.G.Teubner

Ritter

F.

Deussen

O.

Preim

B.

and

Strothotte

T.

Virtual

puzzles

A

new

method

for

exploring

geometric

models

in

vr

IEEE

Computer

Graphics

Applications

-LRB-

-RRB-

September/October

Ritter

F.

Preim

B.

Deussen

O.

and

Strothotte

T.

Using

a

puzzle

as

a

metaphor

for

learning

spatial

relations

In

Fels

S.S.

and

Poulin

P.

editors

Proc

of

Graphics

Interface

-LRB-

Montr

al

May

-RRB-

pages

Morgan

Kaufmann

Publishers

San

Francisco

Seligmann

D.D.

and

Feiner

S.

Automated

generation

of

intent-based

illustrations

In

Proc

of

ACM

SIG-GRAPH

Conference

on

Computer

Graphics

-LRB-

Las

Vegas

July

-RRB-

pages

ACM

Press

New

York

Stone

M.C.

Fishkin

K.

and

Bier

E.A.

The

moveable

filter

as

a

user

interface

tool

In

Plaisant

C.

editor

Proc

of

ACM

CHI

Conference

on

Human

Factors

in

Computing

Systems

-LRB-

Boston

April

-RRB-

pages

ACM

Press

New

York

Strothotte

T.

and

Schlechtweg

S.

Non-Photorealistic

Computer

Graphics

Modeling

Rendering

and

Animation

Morgan

Kaufmann

Publishers

San

Francisco

Viega

J.

Conway

M.J.

Williams

G.

and

Pausch

R.

magic

lenses

In

Proc

of

ACM

Symposium

on

User

Interface

and

Software

Technology

-LRB-

Seattle

November

-RRB-

pages

ACM

Press

New

York

Wanger

L.R.

The

effect

of

shadow

quality

on

the

perception

of

spatial

relationships

in

computer

generated

imagery

In

Proc

of

Symposium

on

Interactive

Graphics

-LRB-

Cambridge

March

-RRB-

pages

ACM

Press

New

York

See

also

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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