Having found maximum value that belongs to area with maximums how to approximate what are the borders of that area?

So we have found an area with at leas开发者_C百科t N points around some center point that fit our criteria on some giant field

(image created with MLDemos and paint) what are algorithms that can be used to get area borders (shown in yellow)? (area is 2d function and algorithm could not know full picture)

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You can use a one-class SVM. LibSVM supports it.

It defines a region that contains X% of the data, where X is provided by the user. During testing, the SVM will tell you whether or not the test data is inside the region.