利用已经加载的特定土地分类的研究区提取随机样本点参与随机森林土地分类。这里我们对于样本点模糊，所以采用直接一个研究区选择随机样本点。然后参与随机森林分类进行土地分类。
函数：
ee.FeatureCollection.randomPoints(region, points, seed, maxError)
Generates points that are uniformly random on the sphere, and within the given region.
生成球体上均匀随机的点，并在给定的区域内。
Arguments:
region (Geometry):
The region to generate points for.
points (Integer, default: 1000):
The number of points to generate.
seed (Long, default: 0):
A seed for the random number generator.
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maxError (ErrorMargin, optional):
The maximum amount of error tolerated when performing any necessary reprojection.
Returns: FeatureCollection
ee.Classifier.smileRandomForest(numberOfTrees, variablesPerSplit, minLeafPopulation, bagFraction, ma