S2 Polyline does not support compressed encoding

[theSloopJohnB]

In the C++ implementation, polylines use version '2' for their compressed format:

https://github.com/google/s2geometry/blob/master/src/s2/s2polyline.cc#L73-L74

static const unsigned char kCurrentCompressedEncodingVersionNumber = 2;

But the Go implementation seems to share polyline and polygon encoding implementations here:

https://github.com/golang/geo/blob/master/s2/encode.go#L29C1-L31C37

// encodingCompressedVersion is the current version of the
// compressed format.
encodingCompressedVersion = int8(4)

So, the Go S2 implementation cannot in fact read the compressed S2 Polyline, because it triggers the version mismatch check:

geo/s2/polyline.go

Line 384 in 5906ab3

if int(version) != int(encodingVersion) {

[jmr]

Do you need decoding, encoding, or both?

[theSloopJohnB]

Just decoding. I have serialized data encoded with the new version that I am unable to read.

…

On Tue, Dec 2, 2025 at 10:09 AM Jesse Rosenstock ***@***.***> wrote: *jmr* left a comment (golang/geo#232) <#232 (comment)> Do you need decoding, encoding, or both? — Reply to this email directly, view it on GitHub <#232 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AGN2PWIVV2X5O5IWZLLOY2L37WTUFAVCNFSM6AAAAACLIDB3VOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTMMBSGUZDSMBYGQ> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[panmari]

@theSloopJohnB would you be willing to give this a go? Would be a great contribution!

[jmr]

I have a version of this pending, but need to test it more.