[gdal-dev] Optimisation of ECW files

[Yves Jacolin (free)]

Le mardi 8 novembre 2011 20:36:06, Even Rouault a écrit :
> Le mardi 08 novembre 2011 11:40:33, Yves Jacolin a écrit :
> > Hello,
> > 
> > I have an issue with one of my project which need some frequent update
> > and I need some advice.
> > 
> > We have a dataset of small ECW files (5 300 files from 30 to 300 ko).
> > This is not the way I want to manage my data to get good performance
> > with MapServer. Too much file, too smal.
> 
> You didn't really say what was the problem with many small files... Why not
> putting them in a tileindex, possibly with an additionnal .qix spatial
> index ?

It seems there was a performance issue with this files. I though using a lot of 
small ECW files was not a good practice. Am I wrong?

> That will be the by far the easier solution to manage the update which is a
> big constraint in your process.
> 
> If you have specific performance problem with the ECW format you could
> probably translate those individual files into anothe format (uncompressed
> tiff, tiff with jpeg compression for example)
ok may be I need to check our performance issue.

Thanks,

Y.
> > All this tiles don't form a regular single tile. I mean some part are
> > hole.
> > 
> > Here is my issues after merging all the tiles:
> > * we lose extent in the final ECW file
> > * we have some black background which is not what expected
> > * we need to update this final tiles frequently, and so we need fast
> > process :)
> > 
> > ECW format doesn't manage nodata so do it mean that I can't have
> > alphaband and so I have no solution to get another background color
> > (white or transparent)?
> > 
> > Does exist some flag to save extent in the final ECW ?
> > 
> > Have you some advice in order to get what I want (alphaband, good
> > perfomance)? I can change file format if needed. We though to use TIFF
> > files with a merge of some of them to get bigger tiles. We can either
> > merge all the tiles, and then merge new tile with this final files or
> > create tileindex for the bigger tiles.
> > 
> > Any hints, advices?
> > 
> > Thanks!
> > 
> > Y.

-- 
Yves Jacolin