Week 11 : Adjusting ODF implementation and looking for solutions on issues found#

What did I do this week?#

I continued to experiment with the ODF glyph implementation. Thanks to one of my mentors I figured out how to get the missing data corresponding to the SH coefficients \(a^l_m\) part of the function \(f(\theta, \phi)\) described here. I also was told to make sure to implement the correct SH basis since there are different definitions from the literature, I have to focus now in the one proposed by Descoteaux, described in this paper, which is labeled in DIPY as descoteaux07. To do this I had to make a small adjustment to the base implementation that I took as a reference, from which I obtained a first result using SH of order 4.

https://user-images.githubusercontent.com/31288525/260909561-fd90033c-018a-465b-bd16-3586bb31ca36.png

It appears that the results on the shape are about the same, except for the direction, but there is still work to be done.

What is coming up next?#

For now, there are 3 things I will continue to work on:

  • The color and lighting. As these objects present curvatures with quite a bit of detail in some cases, this is something that requires more specific lighting work, in addition to having now not only one color but a color map.

  • The scaling. This is something I still don’t know how to deal with. I had to adjust it manually for now, but the idea is to find a relationship between the coefficients and the final object size so it can be automatically scaled, or maybe there is a proper way to pre-process this data before passing it to the shaders to get the right result at once.

  • How to pass the information of the coefficients efficiently. Right now I’m creating one actor per glyph since I’m using a uniform array to pass the coefficients, but the idea is to pass all the data at once. I found several ideas ideas here of how to pass a list of values to the fragment shader directly, I just need to explore deeper how this can be done on FURY, and see which option is most suitable.

Did I get stuck anywhere?#

All the points mentioned above are things that I tried to fix, however, it is something that I need to look at in much more detail and that I know is going to take me some time to understand and test before I get to the expected result. I hope to get some ideas from my mentors and fellow GSoC contributors on how I can proceed to deal with each of the problems.