part i · pdf filetauchi – tampere unit for computer-human interaction forces usually...

TAUCHI – Tampere Unit for Computer-Human Interaction

Part I

IntroductionDevicesLibraries

X3D + Python basics


Haptics

● Incorporate sense of touch into computer use through force or tactile feedback.

● Can be achieved with special hardware: haptic devices.

● Wide spectrum of possible application areas: simulation, CAD / modeling, assistive tech., games.


Forces

● Usually used to resist or assist motion.

● Common approach is to monitor the location of

the device and it's relationship to the objects in

the virtual environment: a good range of possible

feedback effects.

● Two main classes of force feedback: motion and

time dependent feedback.


Motion dependent forces

● Spring - “force exerted by the spring is in direct opposition to the direction of displacement. It is called a "restoring force", as it tends to restore the system to equilibrium.”

● Damper - “a force synchronous with the velocity of the object but opposite in direction

to it... force F may be related to the velocity v by F = -cv, where c is the damping coefficient,

given in units of newton-seconds per meter.”

● Friction - “Friction is the force resisting the relative motion of solid surfaces, fluid

layers, and/or material elements sliding against each other.”

● Inertia - “In common usage the term "inertia" may refer to an object's "amount of

resistance to change in velocity" (which is quantified by its mass), or sometimes to its

momentum, depending on the context.”


Time dependent forces

● Constant

● Periodic

● Impulses - “the integral of a force with respect to time. When a force is applied to a

rigid body it changes the momentum of that body. A small force applied for a long time can

produce the same momentum change as a large force applied briefly”


Force basics

● The system tracks the end-effector.

● When the effector contacts a solid surface the virtual effector proxy is placed in the contact point.

● A spring force is created to push the end effector towards the proxy.

Solid Object

End EffectorContact point

(Source: OpenHaptics programmers guide)


Haptic devicesPhantom

● 6DOF● 2 devices: Desktop &

Premium● Large work-area● Very wide range for

feedback

Image by SensAble


Haptic devicesOmega

● 3DOF

● Sturdy

● Large work-area

● Wide range of feedback effects


Haptic devicesFalcon

● 3DOF

● Cheap

● Gaming

● Good range of feedback effects

● Small


Haptic libraries

● Chai3D OpenSource *● OpenHaptics Comm. / Free for academics *● Reachin Commercial ● H3D OpenSource *● Falcon SDK free for non-commercial use *


Haptic libraries

● Most of the libraries offer both the graphical and haptic output.

● There usually is two execution loops: one loop for graphics and the other for the haptics.

● Haptic loop must execute at least 1000 times per second. Dropping below 1000 Hz causes all kinds of problems ranging from solid surfaces being less solid to weird force-effects.


H3Dhttp://www.h3dapi.org


H3D

● Supports various haptic renderers such as Chai3D and OpenHaptics

● The bottom level is the haptic-only library HAPI

● Uses scene-graph for setting up the environment

● Available also: VHTK (volume haptics toolkit) and UI component library

OpenHaptics Chai3D

H3DApi

HAPI

H3DUtil

Falcon


Scene-graph the H3D way

• Single root node• Child nodes and grouping nodes• Transform has its local coordinate system• Possibility for scripting

Root

Group Transform Script

Object Object Object Object


Levels of H3D: X3D

<?xml version="1.0" encoding="UTF-8"?><Group> <Transform translation="−0.1 0 0"> <Shape> <Appearance> <Material DEF="MAT1"diffuseColor="1 0 0"/> </Appearance> <Box size="0.1 0.1 0.1"/> </Shape> </Transform></Group>

The highest level for creating virtual environment


Levels of H3D: X3D + Python

You can add scripted behavior to X3D files using Python

<?xml version="1.0" encoding="UTF-8"?><Group>

... <PythonScript DEF="PS" url="script.py" /></Group>

from H3D import *from H3DInterface import *

...


Levels of H3D: C++

You can use C++ on many levels, for example:

● Load a X3D file and display it

● Load X3D file + add some elements in it and display it

● Load X3D file + add some elements and route events to C++ handlers then display it

● Create scene-graph, add elements and display it

● Create custom shapes, surfaces etc. and use them in your application (from C++ or X3D)


Levels of H3D: C++

AutoRef< Scene > scene( new Scene );GLUTWindow *glwindow = new GLUTWindow;scene->window->push_back( glwindow );scene->sceneRoot->setValue( myGroup.get() );Scene::mainLoop();


Levels H3D: C++ + X3D + Python

● You can also include a Python script in the X3D file even when loading the file in C++.

● Transferring data from Python to C++ or vice versa is a very tricky, but not impossible


H3D basics


Loading X3D files

● H3D comes with two executable programs: H3DLoad and H3DView

● H3DLoad is a commandline program that you can execute (from command prompt with the x3d filename) or drop the x3d file over the executable

● H3DView is a graphical interface for loading and executing the x3d files

● Both programs come with source files. Extending H3DLoad is easy and preferred way of starting out (in case you need C++ functionality)


Fields

Fields are the fundamental building block. The application is built around a notion of network of connected fields.

Fields can:● Store data ● Be dependent of other field● Have functional behavior


Fields

● To make a connection between two fields one creates a route from a field to another

● Typically one can create a route only between the same type of fields

● Connections can be unrouted


Fields

Fields use lazy evaluation:

● the value is updated only when it is asked to (with the getValue() function for example).

● When the getValue() is called the field either returns current value (when the field is up to date) or update the field by calling the source field's update() function.

Field A

Field B

Field C

Field D Field E


Field template modifiers

AutoUpdate: process event immediately

Class MyField( AutoUpdate( SFFloat) ):def update(self, event):

return event.getValue()


Field template modifiers

TypedField● Typical fields has to be of same type the incoming connections are

● Multiple incoming connections● Specified return type may differ from the incoming connections

Class MyField( TypedField( SFBool, (SFFloat, SFVec3f ) ) ):def update(self, event):

routes_in = getRoutesIn()value = routes_in[0].getValue()return SFBool(True)

Return value 1st input2nd input


Field member functions

● route, connect field to another, trigger an event

● routeNoEvent, same as above, no event● unroute, disconnect a field from another● touch, trigger update event


Nodes

Nodes are collections of fields. Fields in a node can be:

● Inbound (write only)● Outbound (read only)● Inbound – Outbound (read / write)● Initialize only (set value only on init,

outbound)


Dissecting X3D file<?xml version="1.0" encoding="UTF-8"?>

<Scene>

<Transform DEF="TRANS" translation="0 0 0">

<Shape>

<Appearance>

<Material diffuseColor="1 0 0" DEF="PALLO1MAT"/>

</Appearance>

<Sphere radius="0.1" solid="true" DEF="SPHERE"/>

</Shape>

</Transform>

<TimeSensor cycleInterval="1" loop="true" enabled="true" DEF="TS"/>

<PositionInterpolator key="0.0, 0.5, 1.0"

keyValue="0.1 0 0 -0.1 0 0 0.1 0 0" DEF="PI"/>

<ROUTE fromNode="TS" fromField="fraction_changed" toNode="PI" toField="set_fraction"/>

<ROUTE fromNode="PI" fromField="value_changed" toNode="TRANS" toField="translation"/>

</Scene>


Important Nodes: Group

A Group node contains children nodes without introducing a new transformation. It is equivalent to a Transform node containing an identity transform.

Useful fields: MFNode [in] addChildren MFNode [in] removeChildren MFNode [in,out] children[]


Important Nodes: Transform

The Transform node is a grouping node that defines a coordinate system for its children. The coordinate system is relative to the coordinate systems of its ancestors.

Useful fields: SFRotation [in,out] rotationSFVec3f [in,out] scale SFRotation [in,out] scaleOrientation SFVec3f [in,out] translationAnd all the fields from the Group Node


Important Nodes: Shape

The Shape node has two fields, appearance and geometry, which are used to create rendered objects in the world.

Geometry contains the graphical as well as (a possible) haptic geometry.

Appearance can contain for example:– Material and texture specification– Haptic representation information


Important Nodes: Shape

<Group> <Shape> <Appearance> <Material diffuseColor="1 0 0" /> <SmoothSurface stiffness="0.1" /> </Appearance> <Sphere radius="0.1"/> </Shape></Group>


Important Nodes: TimeSensor

TimeSensor nodes generate events as time passes. ● driving continuous simulations and animations● controlling periodic activities ● initiating single occurrence events

Useful fields:SFTime [in,out] cycleInterval SFBool [in,out] enabledSFBool [in,out] loop SFTime [out] cycleTimeSFFloat [out] fraction_changedSFTime [out] time


Sensors & interpolators: example

<Group>

<Shape>

<Appearance>


<SmoothSurface/>

</Appearance>


</Shape>

</Group>


<ColorInterpolator key="0.0, 0.5, 1.0" keyValue="1 0 0 0 1 0 0 0 1" DEF="CI"/>

<ROUTE fromNode="TS" fromField="fraction_changed" toNode="CI" toField="set_fraction"/>

<ROUTE fromNode="CI" fromField="value_changed" toNode="PALLO1MAT" toField="diffuseColor"/>


Important Nodes: Interpolators

–ColorInterpolator, color entries–CoordinateInterpolator, 3D coordinate entries–CoordinateInterpolator2D, 2D coordinate entries–NormalInterpolator, normalized vectors–OrientationInterpolator, rotation values–PositionInterpolator, 3D vectors –PositionInterpolator2D, 2D vectors–ScalarInterpolator, float values


More sensors

● VisibilitySensor: detects visibility changes of a rectangular box as the user navigates the world (enterTime, exitTime)

● ProximitySensor: generates events when the viewer enters, exits, and moves within a box-shaped region in space.


Important Nodes: DynamicTransform

The DynamicTransform node is a Shape container that has basic properties for defining rigid body motion. This includes a position, orientation, mass, etc.

Useful fields: SFVec3f [in, out] position

SFRotation [in, out] orientation

SFVec3f [out] velocity

SFVec3f [in, out] momentum

SFVec3f [in, out] force

SFVec3f [out] angularVelocity

SFVec3f [in, out] angularMomentum

SFSpin [out] spin

SFVec3f [in, out] torque

SFFloat [in, out] mass

SFMatrix3f [in, out] inertiaTensor

SFMotion [??] motion

And all the fields from the Group Node


X3D & Python


X3D & Python

● Define the scene with X3D markup language● Add scripted behavior with Python

Limitations: ● No new surfaces, geometries etc. ● Might slow down the larger systems if all functionality

is scripted


X3D + Python: example<?xml version="1.0" encoding="UTF-8"?><Transform translation="0 0 -0.1"><Group> <DynamicTransform mass="20" inertiaTensor="0.1 0 0 0 0.1 0 0 0 0.1"> <Shape> <Appearance> <Material diffuseColor="1 0 0" DEF="VARI"/> <FrictionalSurface dynamicFriction="0.6" staticFriction="0.2"/> </Appearance> <Box DEF="BOX" size="0.2 0.2 0.2"/> </Shape> </DynamicTransform> <PythonScript DEF="PS" url="pressure.py" /> <ROUTE fromNode="BOX" fromField="force" toNode="PS" toField="pressurePoint" /> <ROUTE fromNode="PS" fromField="pressurePoint" toNode="VARI" toField="diffuseColor" /></Group></Transform>


X3D + Python: example

from H3DInterface import *

class MyForceSensor(TypedField(SFColor,MFVec3f)):

def update(self,event):

force = event.getValue()

if(len(force)>0):force = max(force[0].x, force[0].y, force[0].z) / 25

else:

force = 0

if(force > 1.0):

force=1.0

return RGB(force, 0.3, 0.3)

pressurePoint = MyForceSensor()


Python tips

The field has member functions getRoutesIn and getRoutesOut.

Global field time contains the current time (from Scene::time)

eventSink is a global field that you can route your fields to. If you do so, the field will be updated once in each scene-graph loop.


More Python tips

PeriodicUpdate is a field template modifier that makes your field to update once in every scene-graph loop.

init function will be run once when the python file is loaded. traverseSG function is called once in every scene-graph loop.


PeriodicUpdate example

class Foobar(PeriodicUpdate(SFColor)):def update(self, event):

print "foo"return event.getValue()

class Func(TypedField(SFColor,SFTime)):def update(self,event):

print "UPDATE"return RGB(random(),random(),

random())periodicfunc = Func()time.route(periodicfunc)


Even More Python tips

The module H3DUtils has some very useful classes and functions. The most important one is the TimerCallback class for which you can add callback functions to be called after a certain period. This is “one-off” function call, that is, the function is removed from the TimerCallback once it has been called.


TimerCallback

from H3DUtil import *

def callfunc(): global timec print “boo!” timec.addCallback(time.getValue()+1, callfunc, [])

timec = TimeCallback()timec.addCallback(time.getValue()+1, callfunc, [])


Accessing the X3D side

You can do a lot of things from within the Python code. You can, for example, access the haptic device and the scene-graph. For example, to add an element to a scene-graph from Python do:

X3D:<Transform DEF="RYHMA">

</Transform>

<PythonScript url="mytimer.py" >

<Group USE="RYHMA" containerField="references"/>

</PythonScript>

Python:globgroup = references.getValue()[0] globgroup.children.push_back(mybox)


Possible applications

•Sculpting•Integrate physics engine to H3D•Implement collision detection (with mass & force?)•CAD / planning / decoration application•Block editor•Heightmap / tile / ?? editor•Origami editor!•A Game (Asteroids, Sokoban, LightsOff ...)•Your own idea?


Next...

–The C++ side of things–Introduction to programming haptics with C++–Simple custom geometries–Simple custom surfaces–And more!


Sample X3D file<?xml version="1.0" encoding="UTF-8"?>

<Scene>

<Transform DEF="TRANS" translation="0 0 0">

<Shape>

<Appearance>


</Appearance>


</Shape>

</Transform>


<PositionInterpolator key="0.0, 0.5, 1.0" keyValue="0.1 0 0 -0.1 0 0 0.1 0 0" DEF="PI"/>

<ROUTE fromNode="TS" fromField="fraction_changed" toNode="PI" toField="set_fraction"/>

<ROUTE fromNode="PI" fromField="value_changed" toNode="TRANS" toField="translation"/>

</X3D>

part i · pdf filetauchi – tampere unit for computer-human interaction forces usually...

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