To actually generate the checkpoint data, use the `sdl_checkpoints.pl` script in the hush3 repo: https://git.hush.is/hush/hush3/src/branch/master/contrib/sdl_checkpoints.pl . It uses the `getblockmerkletree` RPC to get the merkle tree data for a block height. It prints the data out in the format that checkpoints.rs wants it in, you simply need to copy and paste the output into the checkpoints.rs file.