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CSC337 Data Visualisation > Flow Visualisation > Flashcards

Flow Visualisation Flashcards

1
Q

What is flow visualisation?

A

Visualizations that trace/makes the patterns of flow/vectors visible.

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2
Q

What is a flow dataset?

A

A spatial dataset of vectors (vector field inside a flow domain)

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3
Q

When are flows unsteady?

A

A flows is unsteady if it varies according to the time dimension (4D)

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4
Q

What is computational fluid dynamics?

A
  • CFD is predicting flow behavior quantitatively.
  • Data is the result of a simulation of flow through or around an object of interest.
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5
Q

What are some examples of objectives/goals in flow visualisation?

A
  • Finding eddy currents
  • Analyzing how flows interfere with objects
  • Determining forces that apply over time over an area
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6
Q

What is the challenge of flow visualisation?

A

To effectively visualise both magnitude and direction simultaneously

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7
Q

List the flow visualisation techniques:

A
  • Arrows visualisation
  • Tufts
  • Advection techniques
  • Image-Based Flow visualisation
  • Path Lines, Streak lines and Time lines
  • Spot noise
  • Line integral Convolution
  • Vector field topology
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8
Q

What are the two flow field representations?

A
  • Lagrangian
  • Eulerian
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9
Q

What is the Lagrangian flow field representation?

A

Sensors move along the flowW

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10
Q

What is the Eulerian flow field representation?

A

Sensors at a fixed location

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11
Q

What is direct flow visualisation?

A

Direct mapping of flow visualisation to mapping space

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12
Q

What are some Eulerian methods?

A
  • Glyphs
  • Arrows
  • Tufts
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13
Q

What is the arrow method (Eulerian) good for?

A

2D flow visualisations. It has easy to understand encoding

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14
Q

What is the arrow method not good for (Eulerian)?

A
  • 3D flow visualisations where the magnitude or velocity changes rapidly
  • Arrows can overlap or obstruct each other
  • Perspective Ambiguity
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15
Q

What are glyps (Eulerian method)?

A

Typically Arrows with more information such as:
- Curvature
- Rotation
More information per voxel

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16
Q

What are tufts (Eulerian method)?

A

Adding light and rigid materials attached to a model. Tufts follow the flow (Cannot be visualized virtually in 3D)

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17
Q

What is Eulerian Particle Progression (advection)?

A
  • At every step k
  • Interpolate the flow direction V(P(k)) at location P(k)
  • Add change in V(P(k)) to P(k)
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18
Q

What is particle advection?

A
  • Calculating the path a particle would take if it was dropped inside of a flow
  • For every step, we calculate the new particle location by adding the velocity vector from the previous position
19
Q

What is the Eulerian Advection equation?

A

V(P(t), t) = dP(t) / dt = P(t + change t) - P(t) / change t

20
Q

What is a path line?

A

A line that is generated by tracing the path of a single particle

21
Q

What are time-lines?

A

A set of particles is released at t=0 and curves are drawn from the successive particle locations.

22
Q

What are streak lines?

A

A line that is made by particles that are continuously inject from a fixed location

23
Q

What are stream lines?

A
  • Records the path particles will take from multiple locations.
  • A snapshot of the flow at a given time.
24
Q

When might lines differ?

A

When they are applied to unsteady flows.

25
Q

What is the issue with evenly-spaced streamline techniques?

A

Be able to produce lines that are spaced pretty evenly

26
Q

What are streamribbon?

A
  • An extension of the idea of advection, a ribbon always tangent to the vector field
  • It displays rotational properties of a flow
27
Q

What are streamtubes?

A
  • Shows convergence and divergences of flow
  • An extension of advection
28
Q

What is the Spot Noise Definition (equation):

A

f (x) = for all i: a_i * h * (x - x_i)
a_i = scaling factor
x_i = random location
h = pulse function
i = spot number

29
Q

What is the spot noise definition with flow accounted for:

A

f (x) = for all i: a_i * h * (x - x_i, v(x_i))

30
Q

What is line integral convolution?

A

Using noise texture convolved along the streamlines of a vector field to show flow directions (2D).

31
Q

What is the algorithm for Line Integral Convultion?

A
  • Noise texture is applied on top of a vector field
  • For every pixel, the noise values along a short streamline are integrated
  • Intensity of a pixel located along the streamline
32
Q

What is the algorithm for fast line integral convolution?

A
  • A first line integral is fully computed
  • The next pixels along the same streamline are incrementally processed by adding and subtraction just one value
  • Redo the same operations on the next streamlines until all pixels have been processed
33
Q

What is the algorithm for 3D line integral convolution?

A

Same algorithm as 2D LIC but use of a 3D noise texture.

34
Q

What is the 2.5D LIC algorithm?

A
  • Algorithm tries to reduce the occlusion issues by visualising flows on curved surfaces
  • A triangular mesh of the surface is created and a flow vector is associaated to every vertex present in the data
  • The mesh is project onto the image plane
  • LIC is computed on the image-plane domain
35
Q

What is oriented LIC?

A

Use of a different convolution filter to show direction of flow.

36
Q

What is vector field topolgy?

A
  • Critical points inside the flow are used to define the flow topology
  • Critical points are points where the vector magnitude is null
  • Critical points are classified from the Jacobian Matrix
37
Q

What are the advantages of direct flow visualisation?

A
  • Simplicity
  • Less computation time
38
Q

What are the disadvantages of direct flow visualisation?

A

Does not always clearly show flow properties.

39
Q

What are image-based flow visualisations?

A

Techniques that capture and analyse visual data of fluid flows using cameras and image processing techniques.

40
Q

What are some image-based flow visualisation techniques?

A
  • Spot noise
  • line integral convoultion
41
Q

What is the spot noise method?

A

A technique that utilises noise textures by randomly adding spots of noise to a vector field, so that the flow warp around the spots.

42
Q

What is the goal of line integral convolution?

A

To visualize steady flows in 2D space on/near the body of an object.

43
Q

What are the drawbacks of Glyps?

A
  • They take up a lot of visual space
  • Limits to how many glyph you can display
  • hard to visualize high turbulent glyph
44
Q

What are the drawbacks of streamlines?

A
  • Placement of streamlines is important
  • Magnitude is not apparent

CSC337 Data Visualisation (14 decks)

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