Android Documentation:
public float metersToEquatorPixels(float meters)
Converts a distance in meters (along the equator) to one in (horizontal) pixels at the current zoomlevel. In the default
Mercator projection, the actual number of pixels for a given distance will get higher as you move away from the equator.
wiki (about Mercator projection):
http://en.wikipedia.org/wiki/Mercator_projection
The scale is proportional to the secant of the latitude φ
So, i use it like
mPixRadius=(myMapView.getProjection().metersToEquatorPixels(mRadius) * (1/ Math.cos(Math.toRadians(mlatitude))));
I test it in some objects. It seems it works. But may be it is mistake?