[GRASS5] r.*.tiff update: tiled tiff support added

Luca Cristelli luca.cristelli at ies.it
Wed Feb 14 16:46:14 EST 2001

Hi all,

I added tiled tiff support to r.in.tiff and r.out.tiff modules.

r.out.tiff has a new flag to force tiled tiff output:

it forces 128x128 pixel tiles output 

if the flag is not specified the module works the old way,
writing tiff files line by line (scanlines).

r.in.tiff detects automatically input tiff file type and
proceed accordingly so no specific flag is needed to read
tiled tiffs.

There are no particular improvements in writing speed, both
methods take the same. You get an enhancement when 
reading very large tiff files and need only a
small region. If tiff file is organized by tiles it's 
easy and fast to retrieve needed tiles. On the other side,
if tiff is scanline based it needs a lot more transfers 
for the same task. If files are compressed this is even
more important. 

I use a web/gis publishing software made by Autodesk called
MapGuide. I did some tests and tiled tiff are 10 to 100 
times faster since MapGuide usually needs a small part of
the whole tiff.
The TIFF standard 
[ http://partners.adobe.com/asn/developer/PDFS/TN/TIFF6.pdf ]
allows tiles of various sizes (even rectangular tiles)but 128x128
is a common value. 
Also compression gains something from tiling. Usually compressing
tiffs by tile gives better results than by scanlines.

Greetings, Luca.

Luca Cristelli                           luca.cristelli at ies.it
I&S Informatica e Servizi                           www.ies.it



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