Classifying sensor data as being associated with ground (as opposed to an object) may comprise determining a number of channels of sensor data that have returns in them, setting a number of control points and a number of knots of a curve based at least in part on the number of channels that have returns, and fitting a curve having the number of control points and the number of knots to the sensor data. The curve may be used to distinguish sensor data associated with the ground from sensor data associated with an object. Determining the curve may additionally or alternatively include limiting an elevation value of a control point and/or knot based on elevation value(s) of the sensor data, weighting the sensor data based at least in part on elevation values associated with the sensor data, and/or adjusting knot spacing, et alia.