The data-extraction step is commonly the slowest step in the process of generating images.
Disk access is optimized in ncWMS by using a data-extraction strategy appropriate to the nature and location of the source data, as described in Fig. 3.
However, the presence of data caches within the underlying operating system and server hardware also has a strong effect (see Fig. 4) – we refer to these caches as “disk caches”.
Fig. 4 shows that it is possible to extract data from a very large dataset (162 million points) for the creation of a 256 × 256 image tile in less than 400 ms, if disk caches are active and the “scanline” strategy is used. The process of turning the data array into an image is much quicker, taking around 30 ms under the same test conditions.