Depth-Dependent Halos: Illustrative Rendering of Dense Line Data
	by Jakob Knapp (01327386) and Ahmed Othman (01325531)

Introduction

In their 2009 paper [1], Everts et al. describe a technique to add depth cues to an illustrative black white rendering of dense line data. As this approach is applied to dense line data sets, one of these being nerve fibre tracks within the human brain, it has certain benefits when compared to using shaded elements.

Our application is an attempt of implementing the ideas of Everts et al. while also adding additional features for experimentation purposes. For instance, we added the option of removing the halos completely and additionally the ability of changing between two different types of tapering. The first form of tapering is the same as the one explained in the paper. For the second form, the lines are made extremely thin, giving the impression of hair-like structures. Also, we extended the program to allow the visualization of point clouds. In this case halos are added to points instead of lines.
 

Interface

To run the application, you just need to click on the VISUALISATION2.exe. An interface will open and per default a line data set and a point data set are loaded and already visualized. By clicking on “File” in the top left corner you can load new datasets, if you wish.

On the left side of the application, you can tweak different parameters to change representation of the data set:

• Reset View: Change camera back to its original position and rotation
• Render Halo: render the data without the halo-technique
• Strip Width: adjust the strip with of the lines
• Depth Cueing: adjusting different depth cuing parameters (like max. line width and min. line width), choosing between exponential and linear depth cueing and specifying the depth cuing falloff
• Data Subset Selection: only render subset of the available lines
• Hair-thin lines: activate the above explained second tapering method

In the upper left corner, you can switch to the point data representation:

• Changing the cone size
• Changing the point diameter

Controls

• Mouse Wheel (scroll): Zoom-In with
• Mouse Wheel (hold): shift the data set around
• Left Mouse Key (hold): rotate data set
• W: move camera forward
• S: move camera backwards
• A: move camera left
• D: move camera right

Data Sets

The files containing the line data is of the Track-File (.trk) format, which is a single binary file. The body of such a file contains a sequence of tracks and the number of points in each of these tracks [2].

The files containing the point data are simple .txt files, where each line contains the 3D coordinates of a single point.

Links:

• Binaries
• Source Code
• Documentation
• Original paper

Additional Libraries:

• TrkFileIO for loading the trk. files

References:

[1] Everts, Maarten H., et al. "Depth-dependent halos: Illustrative rendering of dense line data." IEEE Transactions on Visualization and Computer Graphics 15.6 (2009): 1299-1306.

[2] Wang, R. and Wedeen, V. (2015). File Format. [online] Trackvis.org. Available at:
http://www.trackvis.org/docs/?subsect=fileformat [Accessed 1 Apr. 2019].