Applications

CFD Sim ulation

Th e SH ARC aircraft is an

experim ental unm anned aerial

veh icle (UAV). In th is exam ple

th e air flow from a com putational

fluid dynam ics s im ulation (CFD)

is explored us ing m ulti-m odal

interaction. W h ile only

s im ple propertie s can be

rendered visually w ith out

cluttering th e display, th e

h aptic fe edback provide

continuous repre s entations

of th e data and ph ys ical guidance th rough out th e volum e .

H eart Blood-flow

M odern M RI-scanners are capable of

aq uiring anim ated blood-flow data

from w ith ing a beating h um an h eart.

Both th e poor tis sue contrast of th is

k ind of data and th e fact th at th e

nois ine s s of M RI data m ak e s

autom atic extraction of feature s

difficult, m ak e s it an intere sting target

for m ulti-m odal m eth ods . Th e h aptic

fe edback h elps th e radiologist

understand th e flow and guide s th e

exploration both ph ys ically and

m entally.

H aptic M ode

FAST AND H IGH PRECISION VOLUME H APTICS

Karljoh an Lundin Palm e rius

Norrk öping Vis ualiz ation and Inte raction Studio

Link öping Unive rs ity, Sw e de n

Proxy-based Volum e H aptics

Proxy-bas ed m eth ods for volum e h aptics us e a

proxy to internally repre s ent th e h aptic probe . Th e

h aptic be h aviour is controlled by m oving th e

proxy and th e force fe edback is calculated from a

virtual spring-dam per connecting th e proxy and

th e probe .

Prim itives Solver

Th e proxy pos ition th at repre s ents th e h aptic fe edback th rough th e virtual spring-dam per for each tim e fram e is found by balancing th e force fe edback from th e spring-

dam per against th e force from th e prim itive s . Th is is done by th e solvers .

H igh Precision Analyth ical Solver

We h ave de s igned an analytical m eth od for solving th e balancing e q uation

and so find th e pos ition of th e proxy. Th is solver m ak e s us e of th e com m on

s ituation w h e re h aptic prim itive s are in configurations th at produce s

orth ogonal constraints .

Th e analytical solver is bas ed on iterative m ovem ents th e proxy point in

accordance w ith th e h aptic prim itive s in turn. During th e s e iterations th e

proxy pos ition repre s ents th e force exerted by th e applied h aptic prim itive s ,

onto th e currently proce s s ed prim itive .

General Num erical Solver

If th e orth ogonality re q uirem ent for th e analytical solver is not fulfilled,

th e solver fails and th e system ne eds to fall back on a m ore general solver

th at is capable of h andling any com bination of h aptic prim itive s , even non-

orth ogonal configurations . Th is is im plem ented us ing a ste epe st de scent

m inim ization of th e balancing betw e en th e fe edback and th e force from th e

prim itive s .

Volum etric Data

Th e volum etric data at th e probed pos ition is extracted to

control th e param eters of th e h aptic prim itive s , th us

indirectly controlling th e h aptic fe edback .

H aptic Prim itives

Th e h aptic prim itive s configured from th e volum etric data propertie s define th e

local h aptic be h aviour w h ich th en reflects th e local data in th e volum e .

Depending on w h ich prim itive s h ave be en s elected as a repre s entation of th e

data, and depending on h ow th e ir param eters are controlled, th e re sulting

h aptic m ode produce s different h aptic be h aviour. Each prim itive h as an

individual strength , direction and pos ition.

Plane Constraint

Th e plane prim itive is a 1D constraint, us ed to

s im ulate surface s .

Line Constraint

Th e line prim itive is a 2D constraint, follow ing th e

"bead on a string" m etaph ore .

Point Constraint

Th e point prim itive is a 3D constraint, providing a

re s istance to m otion in any direction.

Directed Force

Th e directed force prim itive

generate s a force is th e

defined direction.

Procedure

1 Put proxy at probe pos ition — zero force fe edback

2 M ove proxy in re spons e to force prim itive s

3 M ove proxy in re spons e to plane prim itive s

4 M ove proxy in re spons e to line prim itive s

5 M ove proxy in re spons e to point prim itive s

Procedure

1 Put proxy at probe pos ition

2 Initialize step length

3 Estim ate re s idual force and m ove th e proxy th e step length in

th e direction of th e re s idual force

4 If th e propagation ch anged direction m ore th an 9 0 degre e s ,

low er step length

5 Repeat 3– 4 until re s idual or step length is low er th an th e

m ach ine eps ilon