Write QDataSets that vary over at most 2 independent variables as a Das2 stream. Since Das2 streams can have at most 2 independent variables, higher dimensional (not necessarily higher rank) QDataSets can't be written using this code. Streams that can be written have the following plane structure X Y [Y Y Y Y ... ] X YScan [YScan YScan YScan ... ] X Y Z [Z Z Z Z ... ] All binary output is streamed in machine-native order. Since datasets written on one architecture are most likely to be read on the same architecture this choice causes the least amount of byte swapping. This is a direct serialization of QDataSet and does not require any legacy das2 dataset classes such as VectorDataset or TableDataset.