Representing Flow

Colin Ware

UNH

We can do better than this

2D vector fields

Vector components Direction Magnitude

Orientation

Vector sign bit

2D Flow visualization• A landmark study

- Image courtesy of Dr.Laidlaw et al.

OrientDirectionMagnitude

Perceptual issues

Luminance contrast for detail Red on green is hard to see (illustrate)

Natural semantics for signalling “more” Longer Wider More dense More contrasty More vivid

The background is critical

Particle systems for flow vis.

Particles are born (randomly in space) Have a behavior (moving with the flow)

They leave a trail (a pathline) Color can change (with speed or age) Width can change (speed or age)

Particles die

movement

form

colordifferences

elementsof form

elementsof movement

colorcolor

1

2&3

4A4B

4C5

6

corti

cal la

yers

Contour finding mechanisms

A single column in V1

Theory of contour finding

Field HayesHess

The next stage – rapid propagation

WeakestContour Signal

Strongest ContourSignal

Prediction

2D Flow visualization• A landmark study

- Image courtesy of Dr.Laidlaw et al.

OrientDirectionMagnitude

How to add VSB?

TerminationsSome neurons respond only with terminations in the receptive field.

Asymmetry along path

Halle’s “little stroaks”

Halle, 1868

Fowler and Ware (1988)

Important factors

Continuity tangential to flow sream

Lightness contrast with background (clarity)

Show direction using asymmetry along path

Use color width | length | contrast | density for speed, or a combination

Add symbols if you like Trace forward and/or

backward.

A real challenge

Many sliders