There’s been some good talk on the mapserver list (thanks to Gregor’s diligent testing) about performance related to serving up raster imagery.

First off, comparisons of image formats. Then a look at some TIFF optimization techniques like overviews (similar to “pyramids” in ESRI land) and internal tiling to boost rendering speed.

Most of the conclusions are not all that staggering:

• TIFF is fastest but takes up more space compared to ECW and JPEG2000.

• Overviews speed up TIFFs tremendously when zoomed out (ie when mapserver would otherwise have to perform some heavy downsampling)

• Internal tiles in GeoTIFF format give a boost when zoomed in (only the necessary tiles are read from disk)

• The TIFF comparison was run on two setups; a monsterous 8-core, RAID-5 equipped beast and a low-memory virtual machine on low-end PC hardware. The TIFF optimizations are very noticeable on the lesser machine but almost completely negligible on the high-end machine.

Both tiling and overviews are useful, but only on machines with resource shortages, such as slow disks or a lack of spare RAM for caching.

Nothing earth-shattering (these techniques are often mentioned as best practices) but is very nice to see some hard numbers to back it up. Plus the verbose test logs provide a good example for a newbie trying to implement them. Good stuff Gregor!