In the terminology of Blower and Clegg (2011) this is a “destination-pull” algorithm.
Other tools (e.g. Panoply, http://www.giss.nasa.gov/tools/panoply/, and Matplotlib, Hunter, 2007) implement “source-push” algorithms, which iterate over the entire source grid and transfer information to the required target data structure.
Source-push algorithms tend to be faster than destination-pull algorithms when the source data grid is smaller than (or equal in size to) the target domain (Blower and Clegg, 2011).
However in the visualization of environmental data, source data grids can be very much larger than the output image; Blower and Clegg (2011) demonstrate that the destination-pull approach can significantly outperform source-push approaches for large datasets. Scalability to large source datasets is a key aim of ncWMS.