Provide proper coord index

[rowanwins]

I had this case recently where I needed the proper coordinate index for polygons with holes. Currently the callback advertises

turf.coordEach(features, function (currentCoord, coordIndex, featureIndex, multiFeatureIndex, geometryIndex) {

But coordIndex just continually increments up as you work through nested rings so you can't find the coordinate properly using indexing.

So there are two options

• Add another argument to the callback at the end, which doesn't require a breaking change (that's the approach taken here)
  • if we go down that route I'll probably rename coordIndex to make it more explicit
• Introduce a breaking change so that coordIndex returns the proper index

In preparing this PR I noticed some comments in the test.js like

turf/packages/turf-meta/test.js

Line 1178 in 9e20dd5

// Coord Index => [0, 1, 2, 3, 4] (Major Release Change v6.x)

and

turf/packages/turf-meta/test.js

Line 1190 in 9e20dd5

// Coord Index => [0, 1, 2, 3, 4] (Major Release Change v6.x)

So someone intended to go for the breaking change at some stage...

I don't have a strong preference either way.

• Use a meaningful title for the pull request. Include the name of the package modified.
• Have read How To Contribute.
• Run npm test at the sub modules where changes have occurred.
• Run npm run lint to ensure code style at the turf module level.

[twelch]

Nice. I like your approach taken. coordIndex as-is seems like it has value so it makes sense to me to just leave it and add a new parameter at the end.

The name coordIndex also seems okay, I don't feel strongly a name change is needed. Perhaps a clarification in the docs what it is if missing?

Consider ringIndex instead of indexOnRing for consistency with the other names.

[rowanwins]

Re naming I was thinking coordIndex perhaps could become index, or absoluteIndex?

Consider ringIndex instead of indexOnRing for consistency with the other names.

I think ringIndex could be confusing because it could be interpreted as which ring (eg an outer ring or a hole)... maybe if we do change the name of the 2 argument this could be named coordIndex?

[JamesLMilner]

I think the approach here is good - would be good to update the docs to document indexInRing. I think the naming conventions used make sense and we probably don't need to change coordIndex (happy for others to disagree).