local function linePlaneIntersect( lineStart, lineEnd, planeNormal, planePoint )
    local d = planeNormal:Dot( lineEnd - lineStart )
    if ( d == 0 ) then return false end
    local t = planeNormal:Dot( planePoint - lineStart ) / d
    if ( t < 0 ) then return false end
    return lineStart + t * ( lineEnd - lineStart )
end