Z-Tiles: Building Blocks for Modular, Pressure-Sensing Floorspaces Bruce Richardson, Krispin Leydon,...

Z-Tiles: Building Blocksfor Modular,

Pressure-Sensing Floorspaces

Bruce Richardson, Krispin Leydon, Mikael Fernström, Joseph A. Paradiso

http://www.idc.ul.ie/ztiles/

Introduction

• New Pressure-

Sensitive Floorspace

• Successor to

Litefoot (1998) &

Magic Carpet (1997)

Paradiso et al. (1997) The Magic Carpet: Physical Sensing for Immersive Environments. CHI’97Griffith and Fernstrom (1998) LiteFoot: A Floor Space for Recording Dance and Controlling Media. ICMC’98.

Authors

Bruce Richardson

Interaction Design Centre, UL.

Krispin Leydon


Mikael Fernström


Joe Paradiso

MIT Media Lab, Boston

Requirement

Scalable => Modular and interchangable

Requirement

Managable => Self-organising and reconfigurable

Requirement

Real-Time => Fast scanning and fast output

• Scan at 100 Hz

• Low latency data routing

• Minimal network overhead

Sensor Units

Z-Tile Circuitry

Z-Tile Architecture

Floor Prototype

QuickTime™ and aDV - PAL decompressor

are needed to see this picture.

Data Bottleneck

• Many wires vs. One wire• Bottleneck at connection point

Options

1. Output only changed pressure readings

2. Group similar pressure readings

Blob Matching

Considerations

• 100 pressure scans/sec

10ms maximum computation time

• Minimum number of parameters

• Accurate blob matching

• Trade off

Close “fit” vs Fewer parameters

Ellipse Matching

• Circles:

Loose fit, few parameters

• Polygons:

Tight fit, many parameters

Ellipses

Ellipses - good compromise

Simple Matching

Average -> Centre

Axes -> Bounding Box

Resultant Ellipse

Results

• Pressures distilled to blobs

• 5 parameters per blob

• Implemented on a microcontroller

>800 scans processed per second

Rate achieved at 1/10 speed

Evaluation

• Processing time to

spare

• Difficulty with

diagonal blobs

• Therefore, look for

better match

Angled Ellipses

Pressure Readings We have We want

General Method

• Determine centre

as before

• Locate 2 most

distant points

• Set this as major

axis

General Method cont’d

• Rotate points so

axis is horizontal

• Use bounding box

to determine major

and minor axes

lengths

Results

• Implemented on microcontroller

• Integer-only calculations

• Lookups for rotations

• Computation time 1-2ms

Summary

• Blob detection to reduce data• 2 ellipse-matching algorithms• Run time on hardware: <2ms

Future Work

• Integrate blob detection algorithm into tile software

• Detect blobs across tiles

Questions?

http://www.idc.ul.ie/

http://www.idc.ul.ie/ztiles/

Z-Tiles: Building Blocks for Modular, Pressure-Sensing Floorspaces Bruce Richardson, Krispin Leydon,...

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