Advanced visualization with VisNow platform Case study #2 3D scalar data visualization

Transcription

1 Advanced visualization with VisNow platform Case study #2 3D scalar data visualization This work is licensed under a Creative Commons Attribution- NonCommercial-NoDerivatives 4.0 International License.

2 Examples 2 3D data on regular grids examples: Physical model: electrostatic field of a quadrupole calculated in a box Medical imaging: Computed Tomography scan of a human foot Aerodynamics supersonic flow over wing edge

3 Simple scalar data reading 3 1. Create VisNow field reader module by dragging from modules library 2. Click browse in module GUI to read ct.vnf file located in sample_data\visnowfields\ folder 3. In the field info tab the information on the field can be found 4. Select all show extern faces boxes in presentation -> content tab and select color extern faces by avg; We have the overall preview of file contents. How can we look inside?

4 Simple scalar data presentation 5. Remove show extern faces option 6. You may choose one of oint grid or line grid options with grid density (coarse/fine/very fine) 7. The presentation is not precise but we may see the general geometry and inside contents 4

5 Regular field slicing 5 Incase of regular grid data we have two modules that can slice the field: regular field slice and interpolated field slice. Regular field slice module presents a logical slice based on a user selected grid index in a field structure. Interpolated field slice interpolates the data on a custom selected plane. In both cases the slice can be coloured with any of the original components.

6 Regular field slicing 6 8. The easiest slice: click RMB on the blue output port (with our 3D field), choose attach->3d field mappers->regular field slice 9. You may now change the slice orientation, position and choose colour map in presentation tab

7 Regular field slicing 7 Regular field slice module selects one of the slice indices with a slider. We only have the three directions of slicing the ij plane, jk plane or ik plane. To create a custom slice use interpolated field slice. This interface consists of resolution sliders of the plane on whitch the dat will be niterpolated and a set of dials, which can be used to rotate, translate and scale the slice plane. You may now select a significantly interesting crosssection e.g. slice just over the soul plane of the foot and paralel ones.

8 Isosurface 8 Isosurface module creates isosurface v(x)=t for a selected component v and threshold t. Warning: if a vector component is selected the isosurface of a vector norm v(x) = t will be calculated The network to create this image consists of the following modules: Test regular field 3D Isosurface Axes 3D Viewer 3D

9 Isosurface Connect the isosurface module (from 3D field mappers) to our 3D field 11. We will see the skeleton outline on the screen a result of default values 12. Get to know the interface of this module

10 Isosurface GUI 10 Choice of a component to draw the isosurface in our example there s only one The threshold interface you already know If the field is quite big (e.g. 512x512x5000) and complex (e.g. noisy) we may use only every n-th node If the isosurface is noisy or sharp-edged it can be smoothed a bit. The uncertainty field can be generated

11 Example foot anatomy 11

12 Volume rendering 12 In volume rendering we obtain an image of the volume in which the colour and the transparency depend on data values. Contrary to the precise presentation with a slice or isosurface we get a synthetic presentation under some uncertainty. A complex interface of this module allows to choose the colour map and a detailed manipulation of transparency transfer function (dependancy of transparency on data component values). In certain case it is useful to use different components for colour and transparency.

13 Volume rendering Create a new volume rendering module and connect in to our 3D field. Just simple parameter tuning shows a correct visualization (change colour map to medical) 14. The most precise modifications of the visual effect is provided by the transparency map manipulation

14 Volume rendering 14 Choice of the data componant mapped to transparency. Range of mapped values. Global transparency of data set by vertical slider. Transparency map drawing window: - draw the function with LMB dragging (red line) - Draw straight lines with shift_lmb dragging - Smooth with RMB - The values histogram is visible in the backgroud. Threshold slider all values below are fully transparent. Gray line shows the resulting transparency map. Visualization of transparency. Predefined maps

15 Potential and transparency 15 Clearly visible areas of high potential (plus/minus) a result of applying a transparency map with centered minimum.

16 Volume rendering and gradients Create a network of differential operations (data filters), modify components/coordinates and volume renderer 16. In differential operations select the gradient of density component (start module with run buton) 17. In modify components/coordinates select split density gradient and click run

17 Volume rendering and gradients 18. In volume renderer module select as transparency component the density_grad (yes, vector components can be used as scalar by vector norm) and notice that uniform areas (e.g. muscles) are transparent while area boundaries are clearly visible. 19. To increase the image plastics we ll apply shading: in datamap tab select one of the gradient coordinates component and grayscale colour map 17

18 visnow.icm.edu.pl Contact: University of Warsaw Bartosz Borucki, Krzysztof Nowiński This work is licensed under a Creative Commons Attribution- NonCommercial-NoDerivatives 4.0 International License.