Axis2D = function (dim, scale, coordExtent, axisType, position) {
    Axis.call(this, dim, scale, coordExtent);
    /**
     * Axis type
     *  - 'category'
     *  - 'value'
     *  - 'time'
     *  - 'log'
     * @type {string}
     */
    this.type = axisType || 'value';

    /**
     * Axis position
     *  - 'top'
     *  - 'bottom'
     *  - 'left'
     *  - 'right'
     */
    this.position = position || 'bottom';
}
Transform global coord to local coord,
i.e. var globalCoord = axis.toLocalCoord(40);
designate by module:echarts/coord/cartesian/Grid.
@type {Function}