Although I still don't know why, but I think I get the right output. I can figure out myself.

Example attached.

        GameObject targetGo = ((OnlineMapsMarker3D)target).instance.gameObject;
        GameObject playerGo = ((OnlineMapsMarker3D)player).instance.gameObject;

        Debug.Log(Vector3.Distance(targetGo.transform.position, playerGo.transform.position));

        Vector2 markerTile = OnlineMapsUtils.LatLongToTilef(target.position, OnlineMaps.instance.zoom);
        Vector2 playerTile = OnlineMapsUtils.LatLongToTilef(player.position, OnlineMaps.instance.zoom);

        Debug.Log(Vector2.Distance(markerTile, playerTile));

the output is: 15.20264 and 0.05957031

lets take ingress as an example:

I want to draw a circle around player and its radius is 500m in real world so player can attack enemy in this range.
How should I project this 500m in the 3D game space? In other world what is the radius of that circle in game space?

Do you mean tile position is the position of maker in 3D world space?

OnlineMapsUtils.DistanceBetweenPoints:
http://infinity-code.com/doxygen/online … bc84a165f2

Example:
http://infinity-code.com/atlas/online-m … ample.html

In my game, I need to detect distance between player marker and other marker. Also I need to draw a circle to around player marker.

So I either have to translate real world markers distance to 3D world distance,  or translate coords to 3D world position to perform calculation.
However I cannot find any api to get those done.

Can you let me know how could I do those?
Thanks,

Alax