The most popular library seems to be heatshrink, at https://github.com/atomicobject/heatshrink. There is a Java implementation at https://github.com/markrileybot/heatshrink-java/

However, the C implementation hasn't been updated in 9 years. Not sure what to make of that. It has a moderate number of issues. But it still seems to be very popular.

Tons of other libraries are available, but this seems the most used.

-corey

On Tue, Jun 18, 2024 at 11:13 AM Chris Thompson via pacsat-dev pacsat-dev@amsat.org wrote:

I think this is worth pursuing. If it's a simple algorithm then we could port to java. Or have a standalone C executable that the ground station runs.

This would mainly be to compress logs, experiment data or telemetry before it is downloaded. Uploading compressed data that the spacecraft can uncompress is a separate use case if we want patch configuration or code.

In a third seperate use case we can already compress large files and upload them for later download. The spacecraft just treats them as binary data and the ground stations do all the work.

73 Chris

On Sun, Jun 16, 2024, 18:39 Corey Minyard via pacsat-dev pacsat-dev@amsat.org wrote:

...

I spent some time looking at implementations of compression algorithms. As Bob pointed out, memory can be an issue with these libraries. I was hoping to say that zlib (gzip) would be suitable, but its minimum memory requirement appears to be 128K. There appears to be a way to reduce that, but it's still probably going to be too big. Later, better algorithms like bzip are going to be even more memory intensive.

I searched around and there are a large number of compression libraries that are free and designed for microcontrollers, with memory requirements in the hundreds of bytes (or even less!). None are as good as even zlib, but they are better than LZW (compress) and would be adequate. Also, more critically, they are designed to compress small amounts of data efficiently. The trouble then becomes finding one with a Java implementation, if we are planning to send the compressed data over the download or uplink.

Is this something worth pursuing?

-corey - AE5KM

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