Finding Features within distance (meter) in FeatureLayer

[ATSIT]

I am working on ArcMobile API (C#) and I want to get all features with in 30 meter distance of point after creating a point object on MAP.

What I am doing is creating
Envelope(CoordinateCentre,hieght,width)
then
CreatingQueryFilter based on that Envelope with GeometricRelationShipType.Intersects
Then passsing this queryfilter to FeatureLayer.

It's not working...! I am note sure that unit of height and width of that envelope is meter or not?
I have done some search and came to know that there exist certain Buffer concept to get this kind of thing but I couldnot find any API in ArcMobile and they exist in GEODATABASE

Anyone has any idea how to do that in ArcMobile
Please help, it's urgent

[CiprianLazar]

The height and width of the envelope that you create are in map's spatial reference units. So if your map's units are meters, your height and width should be 30. But if for example your map's coordinate system is WGS84, than your units are degrees and not meters. You should use a much smaller value than 30 to approximate 30 meters (something like 0.0003).