[mapserver-users] preparing orthos for Mapserver?

[Frank Warmerdam]

On Sat, Oct 5, 2013 at 3:31 AM, Rahkonen Jukka
<jukka.rahkonen at mmmtike.fi> wrote:
> Hi,
>
> Have also definitely a try with JPEG compressed tiffs. You can save 90% of the disk space with nominal effect on speed and quality, but that depends on your hardware and imagery.  It is still worth testing. The command to use is
> gdal_translate -of GTiff -co tiled=yes -co compress=JPEG -co photometric=YCBCR
>
> For overviews use
> gdaladdo -r average -ro --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR
>
> With or without -ro is a matter of taste. By using internal overviews you will save a bit more space because external overviews have some ballast but if you want to archive images sometimes you can discard the external overviews and save some disk space by that time.
>
> Tiffs are not as hopeless than plain JPEGs of PNGs and images do not need to be read totally into memory.
> Untiled tiffs are usually written in stripes so for reading a box from an arbitrary place inside the image it is enough to read all the scan lines which intersect that box. It is still more data than what is needed with tiled images.
>
> There are also clever tiff readers which can read fast, let's say, every 10th row and column from uncompressed tiff and create an subsampled, nearest neighbour subsample in-the-fly. I have used one such in the 90's and Intel 386 computers could handle pretty well uncompressed tiffs of size 10000x10000 pizels without overviews. I think that GDAL can't do that kind of selecting and this is more nice-to-know stuff from the stone age. What to remember is that tiles and overviews are essential for GDAL and Mapserver.

Folks,

Great advice from Jukka, and I'd just note that GDAL
*will* efficiently pull out reduced resolution images on
the fly without overviews if you have a file organized
with a one scanline block even in the year 2013.  For
map serving you are still much better off for several
reasons with the tiles+overviews approach, but I do
love the properly that a one-block-scanline file can be
quickly subsamled by viewer applications like OpenEV
and QGIS.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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