L.Proj.CRS is missing distance method

[perliedman]

In Leaflet 1.0, a CRS is expected to implement the method distance, which calculates the distance between two L.LatLngs, see L.CRS.Earth for example.

I think the easy and "correct enough" fix is to just set L.Proj.CRS.distance = L.CRS.Earth.distance, which will use the haversine formula for all projections.

An alternative, more complicated, but at least in some sense more correct solution, which uses the fact that distances are preserved by some projections, would be to project each LatLng, finding the differences dx and dy and doing d = Math.sqrt(dx*dx+dy*dy), but some problems need to be solved:

• This doesn't apply to all projections, both EPSG:3857 and EPSG:4326 can for example be used with Proj4Leaflet, where this is not true, just to give an example.
• Some projections where this is true still use weird units, like feet, and the result must be scaled so that distance still returns its result in meters

I'd vote for just using L.CRS.Earth.distance until we find some use case were it would cause a problem.

[emacgillavry]

Updated the gist http://bl.ocks.org/emacgillavry/1a654b76d35deceb9bec. The scalebar does appear and no error message. However, I simply get the stock image it seems: no lengths indicated. Am I missing something?

[perliedman]

Yeah, L.CRS.Earth.distance uses a constant, R, which it expects to be part of this, which it isn't with my hack.

Again, this is super-ugly, but works as a workaround:

RD.distance = L.CRS.Earth.distance;
RD.R = 6378137;

[emacgillavry]

Updated the gist and it works beatifully. Have added 100 meter grid layer
as a reference. Thank you very much for looking into this.

On 15 December 2015 at 13:58, Per Liedman notifications@github.com wrote:

Yeah, L.CRS.Earth.distance uses a constant, R, which it expects to be
part of this, which it isn't with my hack.

Again, this is super-ugly, but works as a workaround:

RD.distance = L.CRS.Earth.distance;
RD.R = 6378137;

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[sivesind]

Any hope of fixing this? It holds back the release of a branch compatible with leaflet 1.0.0 beta, #90.

[pthorin]

Closed in #126.