VS: [UMN_MAPSERVER-USERS] VS: [UMN_MAPSERVER-USERS] PHP Mapscript - Jpeg2000

[Rahkonen Jukka]

> 
> On 12/15/05, Rahkonen Jukka <Jukka.Rahkonen at mmmtike.fi> wrote:
> > But there is one thing I am not happy with: creating 
> overviews with gdaladdo is painfully slow. It took 20 hours 
> with 3 GHz Pentium to build those  32 64 128 256 overviews 
> for my virtual raster layer. I think that is awfully long 
> time. But fortunately I am almost sure that this speed could 
> be dramatically improved. I made another test with Kakadu 
> executables, and taking out a 1:32 downsampled version of one 
> image file took no more than 2 seconds. For those who know 
> Kakadu, my command was "kdu_expand -reduce 5 -i test.jp2 -o 
> reduce.ppm".  Based on that I estimated that creating an 
> usable overview file for my set should not take very much 
> longer than [113 (images) x 2 (seconds per image) x 4 
> (downsampling levels)] = 900 seconds = 15 minutes. It would 
> be quite an improvement, compared to 20 hours! Who will be 
> the one to implement it? I cannot, I am no programmer.
> 
> Jukka,
> 
> JPEG2000 reading is quite sensitive to the particulars of
> how the reading is done.   Particular image access patterns
> can be dramatically slower than others.  I suspect that is
> part of the issue with the slow overview building.
> 
> The other thing to keep in mind is that the .vrt mechanism
> was not intended to scale up to hundreds of input images.
> Under some circumstances it may exhibit quite poor performance.
> 
> Best regards,
> --
> ---------------------------------------+----------------------
> ----------------
> I set the clouds in motion - turn up   | Frank Warmerdam, 
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial 
> Programmer for Rent



Frank,

OK, I understand that using gdaladdo will possibly never be especially
efficient tool to create overviews for my jpeg2000 coverage because I am
going to exceed the limits of .vrt mechanism. And gdaladdo do not
understand MapServer tileindexes at all. If I would like to create
overviews anyway (in reasonable time), so do you think I could start
with tileindex system and MapServer? Just ask it to send an image of
suitable resolution covering the whole area, store the file and use that
as overview image as a separate layer? If I then play with MIN and MAX
scales of the layers to switch at some moment from overview image to
jpeg2000 tileindex I might get a good result.

Regards,

Jukka Rahkonen