Remove geojson, go polyline only

[freenerd]

I think we should remove geojson responses and only go with polylines.

Arguments for removal:

• Polylines are way faster to transfer, especially with big responses the cost of serializing and transferring geojson is huge.
• There are easy to use polyline encoders available for all major platforms.
• Removing parameter and code paths makes OSRM leaner and easier to develop.

Arguments against removal:

• For developers to get started, Geojson is easier to work with than Polyline
• There is confusion around the polyline coordinate order (it's lat,lon instead of the lon,lat we use everywhere. This is usually not a problem when developers use libraries for parsing the polyline.
• There is confusion around polyline precision, but since we switched to the standard precision 5 this should be fine now.

/cc @TheMarex

[daniel-j-h]

If you're concerned with response sizes and making OSRM leaner we should talk about

• No JSON only C++ types in the libosrm API Clean libosrm from concepts and dependencies external to library's design #2029
• node-osrm bindings can then decide on response format and e.g. also provide Protobuf blobs

[gardster]

Hi. Please, do not remove GeoJSON support. I think, that you underestimate what this format means for other developers! I want to add several additional arguments, against removal:

• MapBox quick visualization tool geojson.io supports only geoJSON. So it is hard to debug geometry in the response without it.
• Many GIS application has native GeoJSON support instead of polyline (QGIS, JSOM and many others)
• You can parse GeoJSON in python without additional libraries, and can not polyline.
• OSRM server returns JSON encoded answer. It is logical to have a complete JSON response.

By the way. Where you switched to precision 5? I found only precision 6 in sources. https://github.com/Project-OSRM/osrm-backend/blob/master/include/util/coordinate.hpp#L43

[TheMarex]

@gardster internally everything is precision 6, but when we emit polyline we support the google format of precision 5. We also have polyline6 which gives you the full internal precision.

[TheMarex]

I think GeoJSON is here to stay after all.