private void compute_height() {
double ground_altitude = cal_data.ground_altitude;
- if (height_series == null && ground_altitude != AltosLib.MISSING) {
+ if (height_series == null && ground_altitude != AltosLib.MISSING && altitude_series != null) {
height_series = add_series(height_name, AltosConvert.height);
for (AltosTimeValue alt : altitude_series)
height_series.add(alt.time, alt.value - ground_altitude);