Computational Astrophysics and Visualization

Visualization: DAY 1

Lecture Notes

Day 1 Lecture Slides

All of the notes from the intro of day 1. This includes some ideas about how to use visualization in your research and an intro to the tools we are going to be using to do our visualizations.

Code

We are going to break up our code into two parts - one part to calculate trajectories and save the info to a text file, and the second part to read in saved data and make png plot images.

PART 1: Calculate the trajectories & Save data

This is exactly the code from "Choose your Own Adventure #1" from Day 4, but with some code to save information about the trajectories in a text file instead of plotting. Feel free to just grab the end bits of this code that does the saving of positions and velocities as your code probably differs in initial conditions.

PART 2: Read data & make plots

This is exactly the end part of the code from "Choose your Own Adventure #1" from Day 4, but instead of generating trajectories it reads in data from the saved text file from PART 1 and plots stuff.

PART 2, GALAXIES: Read data & make plots

If you worked with galaxy mergers last week, use this code to generate movies from saved data. See the "Resources" section for the data download. Note - its a 77Mb zip file.

FFmpeg Instructions

Step 1: Download FFmpeg from here. There are binaries for most distributions under "Get the packages" so select one that matches your OS.

Step 2: Once you have a series of images generated from the "Code" section above, you can create a movie with the following (assuming /FFMPEG_DIRECTORY/ is the directory where FFmpeg unpacks):

  • /FFMPEG_DIRECTORY/ffmpeg -framerate 15 -pattern_type glob -i 'traj*.png' -c:v libx264 -pix_fmt yuv420p out.mp4
    • The above is for a Mac, but the calling sequence might be slightly different on your OS, so let someone know if it doesn't work and we can take a look at it.

    Note: If you get a "width not divisible by 2" error, this means your saved images have a height or width that is not divisible by 2. You can solve this with a comment such as (if the width is not divisible by 2):

  • /FFMPEG_DIRECTORY/ffmpeg -framerate 15 -pattern_type glob -i 'traj*.png' -vf "crop=in_w-1:in_h" -c:v libx264 -pix_fmt yuv420p out.mp4
    • But certainly let someone know if this doesn't fix the problem.

    Also, check out "Resources" section for some FFmpeg links.

    Resources

    Download FFmpeg

    The main download site.

    Images to Movie with FFmpeg

    Lots of information about what the different parameters are for using FFmpeg to make a movie from a series of png files.

    Other Movie Resources

    A list of other movie making resources if you HATE FFmpeg.

    Download Galaxy Merger data

    77Mb of galaxy merger awesomeness.