Add coordMap function to complement coordEach

Explaination

Hey :)

Yesterday, searching for a tool to loop and map over coordinates, I did not succeed to find one.

The idea was basically simple : loop over all coordinates, and map each of them with a new item (new position, i.e); but the key part is leaving the whole geojson object untouched

I can think of 3 example use-cases, including mines :

• Reproject a whole GeoJSON object
• Remove z ([lng, lat, z]) from coordinates in a whole, dirty, GeoJSON object
• Round coordinates to 6 decimal places into a whole GeoJSON object
• (do the 3 previous operations in a single motion, to improve performance)

I found coordsEach (which just loop), coordsReduce (which would suffice to recompose a new geojson, with indexes and stuff, but would not be very readable), and perliedman/reproject (which is too linked with reprojection stuff, and provide a too-rough cloning strategy IMHO). FYI I opened an issue there to propose extraction of "mapping coordinates logic" in another repo.

I ended up implementing it myself, but I think it could be a great addition to @turfjs 😄

Here is it : traverse-geojson

I used some gjtk tools, and the implementation is very basic. I'd like to use @turfjs formalism and helpers (invariants, etc.), but I'm not really used to it.

API

coordsMap(input, transformer) => returns output (same shape as input)

Params

• input : GeoJSON (FeatureCollection<Any>|Geometry<Any>|Coordinates<Any>|Position|GeometryCollection)
• transfomer : function(position) => returns transformedPosition
  • position : [lng, lat[, ...rest]]
  • transformedPosition : any, ideally a position
• output : GeoJSON<Any>, exact input deep clone, with only coordinates mapped through transformer

Questions :

Is that a good idea ?

Could it be integrated into turf ?

What about also featuresMap, which would basically do the same stuff, but with features ?

Start by reviewing the existing coordEach and coordsReduce APIs, then compare the linked traverse-geojson implementation. Done means adding a coordsMap operation that returns a deep-cloned GeoJSON value with only coordinates transformed, while preserving the input shape and supporting the listed input forms.