using mercator format : srid =900913

Library has actually conversions for several coordinate systems, including Spherical Mercator what you mean here. However, these are converting coordinates to/from map image pixels (which are depending on map zoom), if you have coordinates in meters then it should be possible to convert them if you know size of pixel.

However, my suggestion would be to use geographical (WGS84, EPSG:4326) coordinates, like API uses directly (regardless of map's projection, this could be anything else). With other coordinate systems there are extra calculations needed which makes phone app slower. If you have data in another system then you should be able to convert them before getting data to the phone? Also: I have never seen Spherical Mercator coordinates in direct use, like projected coordinates in meters.

By the way, "Google's/Web Spherical Mercator" code is officially now EPSG:3785, so library uses this number, essentially it is same as 900913. Proper Mercator what geographers use something else, it is not spherical but uses some ellipsoid. Mercator with WGS84 Ellipsoid (EPSG:3395) is also supported in Lib SDK, and you can add also your custom projections to the library.

thanks you very much,

i've an another problem which is :

Let the point be C (Cx,Cy) and the line be AB (Ax,Ay) to (Bx,By).
Let P be the point of perpendicular projection of C on AB

it seems that my point P is not good, [AB] and [PC] are not perpendicular, do you have an idea why ? do you have a solution ?

http://www.codeguru.com/forum/printthread.php?t=194400

public Point distanceToSegment(Point C, Point A, Point B){

double distAB_X=B.x-A.x;
double distAB_Y=B.y-A.y;

double L= Math.sqrt( (float)(distAB_X*distAB_X + distAB_Y*distAB_Y) );

double r = ( (A.y-C.y)*(A.y-B.y)-(A.x-C.x)*distAB_X )/(L*L);

if(r<0 || r>1)return null;
System.out.println("distoseg "+r);

Point5D p=new Point5D();
p.x = A.x + r*distAB_X;
p.y = A.y + r*distAB_Y;
return p;
}

about the distortion, how do you say that you are at Z altitude ?

new WgsPoint(longi,latt, altitude ? )

sorry you speak about lattitude ......

and what about meters wgs84 ? what is the distortion about that in center europe ?

About converting coordinates between projections see also http://www.nutiteq.com/epsg90013-epsg4326#comment-590 Similar approach can be used also for other possible conversions.