Thanks Peter, this is really useful. Do you have any real-world
benchmarks for MapServer that compare regular file access with vsicurl
access, using optimized Geotifs? I've seen the tests for GDAL at
https://trac.osgeo.org/gdal/wiki/CloudOptimizedGeoTIFF, but what about
servering large map-sets over the web?
On 8/30/2019 5:20 PM, Peter Schmitt wrote:
Hi Jan,
On Fri, Aug 30, 2019 at 6:20 AM Jan Hartmann <j.l.h.hartm...@uva.nl
<mailto:j.l.h.hartm...@uva.nl>> wrote:
Hi Pete, could you explain what you mean by "cloud-optimized geotiffs?
A Cloud Optimized GeoTIFF (COG) is a regular GeoTIFF file in which the
data is structured for fast random access. Some properties of a COG
have always been useful for MapServer (Internally tiled & images have
overview levels). Other properties of a COG optimize for cloud access
via GDAL's /vsicurl/ virtual filesystem (Image File Directories of the
GeoTIFF are structured such that one HTTP request can fetch all the
metadata needed to read subsequent blocks from an image). This layout
has been codified somewhat recently... Find out more here:
1. The COGEO organization summarizes things: https://www.cogeo.org
<https://www.cogeo.org/>
2. This GDAL page talks about how to take a normal GeoTIFF, make it a
COG and how to validate that a given GeoTIFF is a COG:
https://trac.osgeo.org/gdal/wiki/CloudOptimizedGeoTIFF
3. GDAL >= 3.1 will have a new COG driver. This provides some
syntactic sugar to generating a COG in a single gdal_translate
command. https://gdal.org/drivers/raster/cog.html
Cheers,
Pete
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