GogChartMap 2D data to canvas coordinate conversion @cx: @cy: @rx: @ry: @th0: @th1: @chart: @area: @axis0: @axis1: @axis2: @fill_area: @Returns: @map: @map: @Returns: @map: @x: @y: @u: @v: @map: @index: @Returns: @map: @Returns: