The decision boundary. Ultimately, the decision boundary of an SVDD is a sphere in the mapped feature space H with radius R ∈ R ≥0 and center c ∈ H. Suppose we observe a new sensor array response vector m ∈ R 2 , and we wish to know if the gas composition that produced it belongs to the normal or anomalous category. The SVDD labels the gas as anomalous if it falls outside the sphere, and normal if inside. Ie., the anomaly detection rule is an indicator function I(•):