VeaaC
commented
3 months ago The default encoding uses url-safe characters, but you could modify it to encode with a different character set. If you only want alpha-numeric characters you only have 62 characters to work with (2 * 26 + 10), though, so you cannot encode 6 bits at a time, but e.g. only 5 (using 32 characters).
If that's what you want you can have a look at the functions that handle the base64 encoding/decoding, e.g. in Rust:
- Encoding: https://github.com/heremaps/flexible-polyline/blob/master/rust/src/lib.rs#L396
- Decoding: https://github.com/heremaps/flexible-polyline/blob/master/rust/src/lib.rs#L490
If you just want to modify the character set, but keep 64 characters then you simply need to replace the character tables/lookups, if you want to switch to only using 32 characters you need to also change the number of bits used (5->4, 6->5, 0x1F -> 0xF, 0x20 -> 0x10, etc)
Be advised, though, that going to a 5-bit encoding is much less efficient. Due to how the variable integer encoding works one bit is reserved, so the 6 bit encoding only has 5 bits payload. Going to a 5-bit encoding will be ~20-30% bigger (depends a lot on you data, it could also double the size if you are unlucky).
Greetings Is it possible to enconde with a different charset? like only include alphanumerical characters?