Vector2 direction = (pointB - pointA).normalized;

This is wrong, because latitude and longitude exist for a sphere or an ellipsoid.
The map is flat and in the Mercator projection.
So you need to first convert the coordinates to the Mercator projection or to the tile position, which is almost the same.

Marker3D.GetTilePosition
or
OnlineMaps.instance.projection.CoordinatesToTile

If Step is big enough, then it doesn't matter that you use a float.
If Step is small, use double.

with PointA & PointB being Marker3D.position of the the center point and the one i'm dragging.

"You need to first convert the geographic coordinates into a tile position, and then calculate the offset."

A tile position ?
Do you mean that instead of using a vector2 "Marker3D.position" i should use 2 doubles, result of "Marker3D.GetTilePosition" ?

So it is a precision issue because of the conversion from double to float ?

FixAngle clamps the latitude and repeats the longitude.

https://media.giphy.com/media/Bq60rkWEq … /giphy.gif

The pink line is a succession of Marker 3D that have been positioned using OnlineMapsUtils.GetCoordinateInDistance.
Those Marker 3D are supposed to be on the red line. As you can see it is working with an angle of 0 or 90 degree from the north.

Here is what i do : 
double nlng, nlat;
float angleFromNorth;
angleFromNorth = Vector2.Angle(Vector2.up, direction);

and in a loop :

OnlineMapsUtils.GetCoordinateInDistance(waypointPlacer.x, waypointPlacer.y, Step, angleFromNorth, out nlng, out nlat);

//waypointPlacer += direction * Step; //What i used to do (it is perfectly working)

waypointPlacer = new Vector2((float)nlng, (float)nlat);

waypointMarker = OnlineMapsControlBase3D.instance.AddMarker3D(waypointPlacer, waypointPrefab);

Could this be a problem caused by the fact that my lat/lng coordinates are stored in a vector2 (and so they are float instead of double, which cause precision lost ? )

So on the bright side my waypoints have now a correct distance between each other, but they doesn't follow the right direction.

PS: What does this function do exactly ?

http://infinity-code.com/doxygen/online … e6292fc96b

Most likely you are looking for OnlineMapsUtils.GetCoordinateInDistance.
http://infinity-code.com/doxygen/online … 48f4e0636b

I want to place Marker 3D at regular interval between two locations (those are defined with  Vector2(longitude, latitude) )

Example:
nextLocation, currentLocation and direction are Vector2
Step is a float, representing the distance i want in meters

What i need to do is basically:  Vector2 nextLocation = currentLocation + direction.normalized*step;

I know that this example ( http://infinity-code.com/atlas/online-m … ample.html ) could be a part of a solution to perform this.
But somehow when i add this script to my Map GameObject it fucked up my scene. (i can't control the map anymore and all i see is a blurry tile).

Aniway i'm pretty sure it would be better to just convert my  'Step' variable from meters to game unit ?
Or, since my location point are (latitude / longitude) should i multiply "Step" with some Lat/Long constant i ignore (so finally my problem is not Unity-unit-related ?)

As you can see i'm getting confused with the best approach to achieve this