使用coord_polar（）时在ggplot2中旋转x轴文本

I am using ggplot2 to plot a scatterplot of many values on a polar axis - coord_polar(). The resulting graph has crowded text because the text is always aligned with the bottom of the page. Is it possible to place the text so that it is printed radially along the polar x-axis? to plot a scatterplot of man