public void Init(Map2d g)
        {
            galaxy    = g;
            xlines    = GridId.XLines(galaxy.TopRight.X);
            xlines[0] = galaxy.TopLeft.X;
            zlines    = GridId.ZLines(galaxy.TopLeft.Y);   // in numeric incr order
            zlines[0] = galaxy.BottomLeft.Y;

            ClickToZoom    = false;
            includedgridid = new List <int>();
        }