geo.extract(x, y, radius=r)

        Return subraster of raster geo around location (x,y) with radius r
        where (x,y) and r are in the same coordinate system as geo

def extract(self, point_x, point_y, radius=0):
        '''
        geo.extract(x, y, radius=r)

        Return subraster of raster geo around location (x,y) with radius r
        where (x,y) and r are in the same coordinate system as geo
        '''
        row, col = map_pixel(point_x, point_y, self.x_cell_size, self.y_cell_size,
                             self.xmin, self.ymax)
        col2 = np.abs(radius/self.x_cell_size).astype(int)
        row2 = np.abs(radius/self.y_cell_size).astype(int)
        return GeoRaster(self.raster[max(row-row2, 0):min(row+row2+1, self.shape[0]), \
                        max(col-col2, 0):min(col+col2+1, self.shape[1])], self.geot,
                        nodata_value=self.nodata_value,\
                        projection=self.projection, datatype=self.datatype)