use use module test_contours() { echo("==== test_contours ===="); min_value = 1; max_value = 360; resolution = 10; function f(x, y) = sin(x) * cos(y) * 30; points = [ for(y = [min_value:resolution:max_value]) [ for(x = [min_value:resolution:max_value]) [x, y, f(x, y)] ] ]; assertEqualPoints([[21, 89.9963, 0], [31, 89.9963, 0]], contours(points, 0)[10]); assertEqualPoints( [[11, 31], [11, 41], [1, 41], [1, 31]], contours(points, [0, 5])[10]); } test_contours();