Spec

[calvinmetcalf]

For implementing a program to convert to topojson in another language a more formalized spec would be helpful. Someone recently asked for this in python so I was curious something beyond the current somewhat narrative description is planned, welcome,in the works, and/or even possible.

[mbostock]

Are you willing to help? I’m not that familiar with the formal language required to write specifications, so I tried to explain it plainly and clearly. But if it’s not clear, then please, by all means, we should fix it.

[calvinmetcalf]

I am willing to help and I did think you explained it well, the ambiguity I saw were things like the structure of the file, with the topology, objects, and arcs as keys. That part isn't documented.

I can at least attempt a formal spec, at least a GeoJSON level of formality to make it easier to write something to make topojson.

[calvinmetcalf]

So not sharing an arc when you could wouldn't break it for someone trying to decode the topojson, my main sticking point was the transform function, which I was able to figure out by viewing the source of topojson, though that's something it might be a good idea to nail down to make writing other encoders easier.

[tbuckl]

oh wait, sorry, i forgot about the "one's complement."

[calvinmetcalf]

I do understand how projections works, my issue is how this particular transformation is defined because any other implementation encoding to topojson needs to transform it in a way that others can transform back.

[timmi]

hi

[tbuckl]

well, i feel doubly dumb...

[calvinmetcalf]

sorry @buckleytom didn't mean to sound snarky with that one, in hind site that's pretty much the only way it could have come across. Don't ever feel dumb when your being helpful.

[tbuckl]

no worries! glad to find help here.

[tbuckl]

also, proj4js looks like an awesome project

[calvinmetcalf]

ok rough draft fyi I wrote this while writing a python port of topojson

[mbostock]

I have created a TopoJSON organization on GitHub, and a new repository topojson/topojson-specification for hosting the specification. I have also added you to a team so that you can edit the draft there, and I will contribute as I have time, probably next week.

[calvinmetcalf]

Thank you!

[mbostock]

Closing this bug. The specification’s not done but we have a home for it now, so can track it over there if desired.