GetGroundZAndNormalFor_3dCoord giving the wrong info

local _ped = PlayerPedId()
local fx,fy,fz = table.unpack(GetEntityCoords(_ped))
local forX = (GetEntityForwardX(_ped) * 10)
local forY = (GetEntityForwardY(_ped) * 10)        
local foundGround, zPos = GetGroundZAndNormalFor_3dCoord(forX,forY,fz)
print("x,y,z ="..fx.." "..fy.." "..fz)  
print("modified xyz = "..forX.." "..forY.." "..zPos,foundGround)   

This is my code. Along with a print so i can identify what they read as.
Can anyone tell me why zPos returns 0.0