openlayers: getCoordinateFromPixel returns different positions with same pixel

I have a feature representing a vehicle which does not move at all on a map. I want, periodically, to retrieve the point’s coordinates located at a constant distance of the vehicle. When the vehicle does not move, the point’s coordinates should be the same.

I use getCoordinatesFromPixel in order to manage to do that, but, although the pixel passed in argument is still the same, the coordinates I get are differents, resulting in some oscillations on screen.

*How to reproduce : * Assuming you’ve got vehMapPos, an array containing the vehicle position (in map units) and map, the Map. On the Map, rotated with any angle, put a feature and center the map on the feature. Then, launch a setInterval. In this interval, do the following :

var elem = document.getElementById('yourMapId');
var clientRect = elem.getBoundingClientRect();
//Getting pixel coordinates
var centerPixelX = clientRect.width/2;
var tierPixelY = clientRect.height/3;
var pixel = [centerPixelX, 2*tierPixelY];


//Problem is here
var point = map.getCoordinateFromPixel(pixel);

//Creating vector from vehicle to pixel
var X = point[0];
var Y = point[1];

var x = vehMapPos[0];
var y = vehMapPos[1];

var vector = {
   'vx': (x-X),
   'vy': (y-Y)
};

//Centering map to the vector coordinates
var mapCenter  = map.getView().getCenter();
var newCenter = [mapCenter[0] + vector.vx, mapCenter[1] - vector.vy];
map.getView.setCenter(newCenter);

I hope this code helps and do no hesitate to question me if you cannot reproduce the bug. It is very annoying, as we’d like to do a GPS functionality.

Regards