openlayers ol3 linestring getLength not returning expected value -

i using getlength retrieve linestring length.

for same segment: 1- when using google map measure tool, 228m 2- when using ign geoportail measure tool, 228m 3- when use e.feature.getgeometry().getlength() 330m

here flat coordinates: e.feature.getgeometry().getflatcoordinates() : [571382.4214041593, 5723486.068714521, 571593.8175605105, 5723741.65502785]

in 4326: [5.132815622245775, 45.644023326845485, 5.134714626228319, 45.64562844964627]

when check coordinates position on either ol3 or google map, same points. difference must come calcul...

did miss , should not use getlength method? please give me direction if think not issue.

geometry.getlength() returns length in map view projection, spherical mercator. spherical mercator distances stretched @ rate of 1/cos(latitude); in example: 228/330 ~ cos(45.64).

to real spherical distance:

var geometry = feature.getgeometry();  alert (geometry.getlength());  // points of geometry (for simplicity assume 2 points) var coordinates = geometry.getcoordinates();  // transform points map projection (usually spherical mercator) wgs84 var mapprojection = map.getview().getprojection(); var t1 = ol.proj.transform(coordinates[0], mapprojection, 'epsg:4326'); var t2 = ol.proj.transform(coordinates[1], mapprojection, 'epsg:4326');  // create sphere measure on var wgs84sphere = new ol.sphere(6378137); // 1 of wgs84 earth radius'  // distance on sphere var dist = wgs84sphere.haversinedistance(t1, t2);  alert (dist); 

for higher accuracy have measure on wgs84 ellipsoid instead of sphere.